diff mbox series

[v7,16/26] PCI: Ignore PCIBIOS_MIN_MEM

Message ID 20200129152937.311162-17-s.miroshnichenko@yadro.com
State New
Headers show
Series PCI: Allow BAR movement during boot and hotplug | expand

Commit Message

Sergei Miroshnichenko Jan. 29, 2020, 3:29 p.m. UTC
BARs and bridge windows are only allowed to be assigned to their
parent bus's bridge windows, going up to the root complex's resources.
So additional limitations on BAR address are not needed, and the
PCIBIOS_MIN_MEM can be ignored.

Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS 1.3 on
Supermicro H11SSL-i via e820__setup_pci_gap():

  [mem 0xebff1000-0xfe9fffff] available for PCI devices

is only suitable for a single RC out of four:

  pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff window]
  pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff window]
  pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff window]
  pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff window]

, which makes the AMD EPYC 7251 unable to boot with this movable BARs
patchset.

Signed-off-by: Sergei Miroshnichenko <s.miroshnichenko@yadro.com>
---
 drivers/pci/setup-res.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Bjorn Helgaas Jan. 30, 2020, 11:52 p.m. UTC | #1
On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei Miroshnichenko wrote:
> BARs and bridge windows are only allowed to be assigned to their
> parent bus's bridge windows, going up to the root complex's resources.
> So additional limitations on BAR address are not needed, and the
> PCIBIOS_MIN_MEM can be ignored.

This is theoretically true, but I don't think we have reliable
information about the host bridge windows in all cases, so
PCIBIOS_MIN_MEM/_IO is something of an approximation.

> Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS 1.3 on
> Supermicro H11SSL-i via e820__setup_pci_gap():
> 
>   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> 
> is only suitable for a single RC out of four:
> 
>   pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff window]
>   pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff window]
>   pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff window]
>   pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff window]
> 
> , which makes the AMD EPYC 7251 unable to boot with this movable BARs
> patchset.

Something's wrong if this system booted before this patch set but not
after.  We shouldn't be doing *anything* with the BARs until we need
to, i.e., until we hot-add a device where we have to move things to
find space for it.

(And we don't want a bisection hole where this system can't boot until
this patch is applied, but I assume that's obvious.)

> Signed-off-by: Sergei Miroshnichenko <s.miroshnichenko@yadro.com>
> ---
>  drivers/pci/setup-res.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> index a7d81816d1ea..4043aab021dd 100644
> --- a/drivers/pci/setup-res.c
> +++ b/drivers/pci/setup-res.c
> @@ -246,12 +246,13 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
>  		int resno, resource_size_t size, resource_size_t align)
>  {
>  	struct resource *res = dev->resource + resno;
> -	resource_size_t min;
> +	resource_size_t min = 0;
>  	int ret;
>  	resource_size_t start = (resource_size_t)-1;
>  	resource_size_t end = 0;
>  
> -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
> +	if (!pci_can_move_bars)
> +		min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;

I don't understand the connection here.  PCIBIOS_MIN_MEM and
PCIBIOS_MIN_IO are basically ways to say "we can't put PCI resources
below this address".

On ACPI systems, the devices in the ACPI namespace are supposed to
tell the OS what resources they use, and obviously the OS should not
assign those resources to anything else.  If Linux handled all those
ACPI resources correctly and in the absence of firmware defects, we
shouldn't need PCIBIOS_MIN_MEM/_IO at all.  But neither of those is
currently true.

It's true that we should be smarter about PCIBIOS_MIN_MEM/_IO, but I
don't think that has anything to do with whether we support *moving*
BARs.  We have to avoid the address space that's already in use in
*all* cases.

>  	if (pci_can_move_bars && dev->subordinate && resno >= PCI_BRIDGE_RESOURCES) {
>  		struct pci_bus *child_bus = dev->subordinate;
> -- 
> 2.24.1
>
Sergei Miroshnichenko Jan. 31, 2020, 6:19 p.m. UTC | #2
On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei Miroshnichenko
> wrote:
> > BARs and bridge windows are only allowed to be assigned to their
> > parent bus's bridge windows, going up to the root complex's
> > resources.
> > So additional limitations on BAR address are not needed, and the
> > PCIBIOS_MIN_MEM can be ignored.
> 
> This is theoretically true, but I don't think we have reliable
> information about the host bridge windows in all cases, so
> PCIBIOS_MIN_MEM/_IO is something of an approximation.
> 
> > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS 1.3 on
> > Supermicro H11SSL-i via e820__setup_pci_gap():
> > 
> >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > 
> > is only suitable for a single RC out of four:
> > 
> >   pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff
> > window]
> >   pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff
> > window]
> >   pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff
> > window]
> >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff
> > window]
> > 
> > , which makes the AMD EPYC 7251 unable to boot with this movable
> > BARs
> > patchset.
> 
> Something's wrong if this system booted before this patch set but not
> after.  We shouldn't be doing *anything* with the BARs until we need
> to, i.e., until we hot-add a device where we have to move things to
> find space for it.
> 

The one breaking boot on this system initially was 17/26 of this
patchset: "PCI: hotplug: Ignore the MEM BAR offsets from
BIOS/bootloader"

Before it the kernel just took BARs pre-assigned by BIOS. In the same
time, the same BIOS reports 0xebff1000-0xfe9fffff as available for PCI
devices, but the real root bridge windows are 0xe8b00000-0xefffffff in
total (and also 64-bit windows) - which are also reported by the same
BIOS. So the kernel was only able to hanble the 0xec000000-0xefffffff
root bus.

With that patch reverted the kernel was able to boot, but unable to
rescan - to reassign BARs actually.

> (And we don't want a bisection hole where this system can't boot
> until
> this patch is applied, but I assume that's obvious.)
> 
> > Signed-off-by: Sergei Miroshnichenko <s.miroshnichenko@yadro.com>
> > ---
> >  drivers/pci/setup-res.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > index a7d81816d1ea..4043aab021dd 100644
> > --- a/drivers/pci/setup-res.c
> > +++ b/drivers/pci/setup-res.c
> > @@ -246,12 +246,13 @@ static int __pci_assign_resource(struct
> > pci_bus *bus, struct pci_dev *dev,
> >  		int resno, resource_size_t size, resource_size_t align)
> >  {
> >  	struct resource *res = dev->resource + resno;
> > -	resource_size_t min;
> > +	resource_size_t min = 0;
> >  	int ret;
> >  	resource_size_t start = (resource_size_t)-1;
> >  	resource_size_t end = 0;
> >  
> > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > PCIBIOS_MIN_MEM;
> > +	if (!pci_can_move_bars)
> > +		min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > PCIBIOS_MIN_MEM;
> 
> I don't understand the connection here.  PCIBIOS_MIN_MEM and
> PCIBIOS_MIN_IO are basically ways to say "we can't put PCI resources
> below this address".
> 
> On ACPI systems, the devices in the ACPI namespace are supposed to
> tell the OS what resources they use, and obviously the OS should not
> assign those resources to anything else.  If Linux handled all those
> ACPI resources correctly and in the absence of firmware defects, we
> shouldn't need PCIBIOS_MIN_MEM/_IO at all.  But neither of those is
> currently true.
> 
> It's true that we should be smarter about PCIBIOS_MIN_MEM/_IO, but I
> don't think that has anything to do with whether we support *moving*
> BARs.  We have to avoid the address space that's already in use in
> *all* cases.
> 

This is connected to the approach of this feature: releasing,
recalculating and reassigning the BARs and bridge windows. If movable
BARs are disabled, this bug doesn't reproduce. And the bug doesn't let
the system boot when BARs are allowed to move. That's why I've tied
these together.

This line setting the "min" to PCIBIOS_MIN_* is there untouched since
the first kernel git commit in 2005 - could it be that all systems are
just fine now, having their root bridge windows set up correctly?

Best regards,
Serge

> >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > PCI_BRIDGE_RESOURCES) {
> >  		struct pci_bus *child_bus = dev->subordinate;
> > -- 
> > 2.24.1
> >
Bjorn Helgaas Jan. 31, 2020, 8:27 p.m. UTC | #3
On Fri, Jan 31, 2020 at 06:19:48PM +0000, Sergei Miroshnichenko wrote:
> On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> > On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei Miroshnichenko
> > wrote:
> > > BARs and bridge windows are only allowed to be assigned to their
> > > parent bus's bridge windows, going up to the root complex's
> > > resources.
> > > So additional limitations on BAR address are not needed, and the
> > > PCIBIOS_MIN_MEM can be ignored.
> > 
> > This is theoretically true, but I don't think we have reliable
> > information about the host bridge windows in all cases, so
> > PCIBIOS_MIN_MEM/_IO is something of an approximation.
> > 
> > > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS 1.3 on
> > > Supermicro H11SSL-i via e820__setup_pci_gap():
> > > 
> > >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > > 
> > > is only suitable for a single RC out of four:
> > > 
> > >   pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff
> > > window]
> > >   pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff
> > > window]
> > >   pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff
> > > window]
> > >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff
> > > window]
> > > 
> > > , which makes the AMD EPYC 7251 unable to boot with this movable
> > > BARs
> > > patchset.
> > 
> > Something's wrong if this system booted before this patch set but not
> > after.  We shouldn't be doing *anything* with the BARs until we need
> > to, i.e., until we hot-add a device where we have to move things to
> > find space for it.
> 
> The one breaking boot on this system initially was 17/26 of this
> patchset: "PCI: hotplug: Ignore the MEM BAR offsets from
> BIOS/bootloader"

I don't think that patch is a good idea.  I think we should read the
current BARs and windows at boot-time and leave them alone unless we
*must* change them.  I don't think we should change things
preemptively to make future hotplug events easier.

> Before it the kernel just took BARs pre-assigned by BIOS. In the same
> time, the same BIOS reports 0xebff1000-0xfe9fffff as available for PCI
> devices, but the real root bridge windows are 0xe8b00000-0xefffffff in
> total (and also 64-bit windows) - which are also reported by the same
> BIOS. So the kernel was only able to handle the 0xec000000-0xefffffff
> root bus.
> 
> With that patch reverted the kernel was able to boot, but unable to
> rescan - to reassign BARs actually.
> 
> > (And we don't want a bisection hole where this system can't boot
> > until
> > this patch is applied, but I assume that's obvious.)
> > 
> > > Signed-off-by: Sergei Miroshnichenko <s.miroshnichenko@yadro.com>
> > > ---
> > >  drivers/pci/setup-res.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > > index a7d81816d1ea..4043aab021dd 100644
> > > --- a/drivers/pci/setup-res.c
> > > +++ b/drivers/pci/setup-res.c
> > > @@ -246,12 +246,13 @@ static int __pci_assign_resource(struct
> > > pci_bus *bus, struct pci_dev *dev,
> > >  		int resno, resource_size_t size, resource_size_t align)
> > >  {
> > >  	struct resource *res = dev->resource + resno;
> > > -	resource_size_t min;
> > > +	resource_size_t min = 0;
> > >  	int ret;
> > >  	resource_size_t start = (resource_size_t)-1;
> > >  	resource_size_t end = 0;
> > >  
> > > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > PCIBIOS_MIN_MEM;
> > > +	if (!pci_can_move_bars)
> > > +		min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > PCIBIOS_MIN_MEM;
> > 
> > I don't understand the connection here.  PCIBIOS_MIN_MEM and
> > PCIBIOS_MIN_IO are basically ways to say "we can't put PCI resources
> > below this address".
> > 
> > On ACPI systems, the devices in the ACPI namespace are supposed to
> > tell the OS what resources they use, and obviously the OS should not
> > assign those resources to anything else.  If Linux handled all those
> > ACPI resources correctly and in the absence of firmware defects, we
> > shouldn't need PCIBIOS_MIN_MEM/_IO at all.  But neither of those is
> > currently true.
> > 
> > It's true that we should be smarter about PCIBIOS_MIN_MEM/_IO, but I
> > don't think that has anything to do with whether we support *moving*
> > BARs.  We have to avoid the address space that's already in use in
> > *all* cases.
> 
> This is connected to the approach of this feature: releasing,
> recalculating and reassigning the BARs and bridge windows. If movable
> BARs are disabled, this bug doesn't reproduce. And the bug doesn't let
> the system boot when BARs are allowed to move. That's why I've tied
> these together.

My point is just that logically this has nothing to do with movable
BARs.

> This line setting the "min" to PCIBIOS_MIN_* is there untouched since
> the first kernel git commit in 2005 - could it be that all systems are
> just fine now, having their root bridge windows set up correctly?

I don't understand the question, sorry.

> > >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > > PCI_BRIDGE_RESOURCES) {
> > >  		struct pci_bus *child_bus = dev->subordinate;
> > > -- 
> > > 2.24.1
> > >
Sergei Miroshnichenko Feb. 5, 2020, 1:04 p.m. UTC | #4
On Fri, 2020-01-31 at 14:27 -0600, Bjorn Helgaas wrote:
> On Fri, Jan 31, 2020 at 06:19:48PM +0000, Sergei Miroshnichenko
> wrote:
> > On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> > > On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei Miroshnichenko
> > > wrote:
> > > > BARs and bridge windows are only allowed to be assigned to
> > > > their
> > > > parent bus's bridge windows, going up to the root complex's
> > > > resources.
> > > > So additional limitations on BAR address are not needed, and
> > > > the
> > > > PCIBIOS_MIN_MEM can be ignored.
> > > 
> > > This is theoretically true, but I don't think we have reliable
> > > information about the host bridge windows in all cases, so
> > > PCIBIOS_MIN_MEM/_IO is something of an approximation.
> > > 
> > > > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS 1.3
> > > > on
> > > > Supermicro H11SSL-i via e820__setup_pci_gap():
> > > > 
> > > >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > > > 
> > > > is only suitable for a single RC out of four:
> > > > 
> > > >   pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff
> > > > window]
> > > >   pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff
> > > > window]
> > > >   pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff
> > > > window]
> > > >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff
> > > > window]
> > > > 
> > > > , which makes the AMD EPYC 7251 unable to boot with this
> > > > movable
> > > > BARs
> > > > patchset.
> > > 
> > > Something's wrong if this system booted before this patch set but
> > > not
> > > after.  We shouldn't be doing *anything* with the BARs until we
> > > need
> > > to, i.e., until we hot-add a device where we have to move things
> > > to
> > > find space for it.
> > 
> > The one breaking boot on this system initially was 17/26 of this
> > patchset: "PCI: hotplug: Ignore the MEM BAR offsets from
> > BIOS/bootloader"
> 
> I don't think that patch is a good idea.  I think we should read the
> current BARs and windows at boot-time and leave them alone unless we
> *must* change them.  I don't think we should change things
> preemptively to make future hotplug events easier.
> 
> > Before it the kernel just took BARs pre-assigned by BIOS. In the
> > same
> > time, the same BIOS reports 0xebff1000-0xfe9fffff as available for
> > PCI
> > devices, but the real root bridge windows are 0xe8b00000-0xefffffff 
> > in
> > total (and also 64-bit windows) - which are also reported by the
> > same
> > BIOS. So the kernel was only able to handle the 0xec000000-
> > 0xefffffff
> > root bus.
> > 
> > With that patch reverted the kernel was able to boot, but unable to
> > rescan - to reassign BARs actually.
> > 
> > > (And we don't want a bisection hole where this system can't boot
> > > until
> > > this patch is applied, but I assume that's obvious.)
> > > 
> > > > Signed-off-by: Sergei Miroshnichenko <
> > > > s.miroshnichenko@yadro.com>
> > > > ---
> > > >  drivers/pci/setup-res.c | 5 +++--
> > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > > > index a7d81816d1ea..4043aab021dd 100644
> > > > --- a/drivers/pci/setup-res.c
> > > > +++ b/drivers/pci/setup-res.c
> > > > @@ -246,12 +246,13 @@ static int __pci_assign_resource(struct
> > > > pci_bus *bus, struct pci_dev *dev,
> > > >  		int resno, resource_size_t size,
> > > > resource_size_t align)
> > > >  {
> > > >  	struct resource *res = dev->resource + resno;
> > > > -	resource_size_t min;
> > > > +	resource_size_t min = 0;
> > > >  	int ret;
> > > >  	resource_size_t start = (resource_size_t)-1;
> > > >  	resource_size_t end = 0;
> > > >  
> > > > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > > PCIBIOS_MIN_MEM;
> > > > +	if (!pci_can_move_bars)
> > > > +		min = (res->flags & IORESOURCE_IO) ?
> > > > PCIBIOS_MIN_IO :
> > > > PCIBIOS_MIN_MEM;
> > > 
> > > I don't understand the connection here.  PCIBIOS_MIN_MEM and
> > > PCIBIOS_MIN_IO are basically ways to say "we can't put PCI
> > > resources
> > > below this address".
> > > 
> > > On ACPI systems, the devices in the ACPI namespace are supposed
> > > to
> > > tell the OS what resources they use, and obviously the OS should
> > > not
> > > assign those resources to anything else.  If Linux handled all
> > > those
> > > ACPI resources correctly and in the absence of firmware defects,
> > > we
> > > shouldn't need PCIBIOS_MIN_MEM/_IO at all.  But neither of those
> > > is
> > > currently true.
> > > 
> > > It's true that we should be smarter about PCIBIOS_MIN_MEM/_IO,
> > > but I
> > > don't think that has anything to do with whether we support
> > > *moving*
> > > BARs.  We have to avoid the address space that's already in use
> > > in
> > > *all* cases.
> > 
> > This is connected to the approach of this feature: releasing,
> > recalculating and reassigning the BARs and bridge windows. If
> > movable
> > BARs are disabled, this bug doesn't reproduce. And the bug doesn't
> > let
> > the system boot when BARs are allowed to move. That's why I've tied
> > these together.
> 
> My point is just that logically this has nothing to do with movable
> BARs.
> 
> > This line setting the "min" to PCIBIOS_MIN_* is there untouched
> > since
> > the first kernel git commit in 2005 - could it be that all systems
> > are
> > just fine now, having their root bridge windows set up correctly?
> 
> I don't understand the question, sorry.
> 


I mean, every BAR assigned here can't reside outside of a host IO/MEM
bridge window, which is a bus->resource[n] set up by the platform code,
and their .start fields are seemed to be duplicated by the
PCIBIOS_MIN_* values - from the platform code as well. But the .start
fields are seem to be correct (aren't they?), and the PCIBIOS_MIN_*
values are sometimes definitely not.

What can be a reliable test to check if PCIBIOS_MIN_* are safe to
ignore unconditionally? Could it be a separate flag instead of the
pci_can_move_bars here?

Would it be fine for a start to ignore the PCIBIOS_MIN_* if it lies
completely outside of host bridge windows? So at least AMD EPYC can
obtain its hotplug power.

Best regards,
Serge

> > > >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > > > PCI_BRIDGE_RESOURCES) {
> > > >  		struct pci_bus *child_bus = dev->subordinate;
> > > > -- 
> > > > 2.24.1
> > > >
Bjorn Helgaas Feb. 5, 2020, 4:32 p.m. UTC | #5
On Wed, Feb 05, 2020 at 01:04:06PM +0000, Sergei Miroshnichenko wrote:
> On Fri, 2020-01-31 at 14:27 -0600, Bjorn Helgaas wrote:
> > On Fri, Jan 31, 2020 at 06:19:48PM +0000, Sergei Miroshnichenko
> > wrote:
> > > On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> > > > On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei Miroshnichenko
> > > > wrote:
> > > > > BARs and bridge windows are only allowed to be assigned to
> > > > > their parent bus's bridge windows, going up to the root
> > > > > complex's resources.  So additional limitations on BAR
> > > > > address are not needed, and the PCIBIOS_MIN_MEM can be
> > > > > ignored.
> > > > 
> > > > This is theoretically true, but I don't think we have reliable
> > > > information about the host bridge windows in all cases, so
> > > > PCIBIOS_MIN_MEM/_IO is something of an approximation.
> > > > 
> > > > > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS
> > > > > 1.3 on Supermicro H11SSL-i via e820__setup_pci_gap():
> > > > > 
> > > > >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > > > > 
> > > > > is only suitable for a single RC out of four:
> > > > > 
> > > > >   pci_bus 0000:00: root bus resource [mem 0xec000000-0xefffffff
> > > > > window]
> > > > >   pci_bus 0000:20: root bus resource [mem 0xeb800000-0xebefffff
> > > > > window]
> > > > >   pci_bus 0000:40: root bus resource [mem 0xeb200000-0xeb5fffff
> > > > > window]
> > > > >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-0xeaffffff
> > > > > window]
> > > > > 
> > > > > , which makes the AMD EPYC 7251 unable to boot with this
> > > > > movable BARs patchset.
> > > > 
> > > > Something's wrong if this system booted before this patch set
> > > > but not after.  We shouldn't be doing *anything* with the BARs
> > > > until we need to, i.e., until we hot-add a device where we
> > > > have to move things to find space for it.
> > > 
> > > The one breaking boot on this system initially was 17/26 of this
> > > patchset: "PCI: hotplug: Ignore the MEM BAR offsets from
> > > BIOS/bootloader"
> > 
> > I don't think that patch is a good idea.  I think we should read the
> > current BARs and windows at boot-time and leave them alone unless we
> > *must* change them.  I don't think we should change things
> > preemptively to make future hotplug events easier.
> > 
> > > Before it the kernel just took BARs pre-assigned by BIOS. In the
> > > same time, the same BIOS reports 0xebff1000-0xfe9fffff as
> > > available for PCI devices, but the real root bridge windows are
> > > 0xe8b00000-0xefffffff in total (and also 64-bit windows) - which
> > > are also reported by the same BIOS. So the kernel was only able
> > > to handle the 0xec000000- 0xefffffff root bus.
> > > 
> > > With that patch reverted the kernel was able to boot, but unable to
> > > rescan - to reassign BARs actually.
> > > 
> > > > (And we don't want a bisection hole where this system can't
> > > > boot until this patch is applied, but I assume that's
> > > > obvious.)
> > > > 
> > > > > Signed-off-by: Sergei Miroshnichenko <
> > > > > s.miroshnichenko@yadro.com>
> > > > > ---
> > > > >  drivers/pci/setup-res.c | 5 +++--
> > > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
> > > > > index a7d81816d1ea..4043aab021dd 100644
> > > > > --- a/drivers/pci/setup-res.c
> > > > > +++ b/drivers/pci/setup-res.c
> > > > > @@ -246,12 +246,13 @@ static int __pci_assign_resource(struct
> > > > > pci_bus *bus, struct pci_dev *dev,
> > > > >  		int resno, resource_size_t size,
> > > > > resource_size_t align)
> > > > >  {
> > > > >  	struct resource *res = dev->resource + resno;
> > > > > -	resource_size_t min;
> > > > > +	resource_size_t min = 0;
> > > > >  	int ret;
> > > > >  	resource_size_t start = (resource_size_t)-1;
> > > > >  	resource_size_t end = 0;
> > > > >  
> > > > > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > > > PCIBIOS_MIN_MEM;
> > > > > +	if (!pci_can_move_bars)
> > > > > +		min = (res->flags & IORESOURCE_IO) ?
> > > > > PCIBIOS_MIN_IO :
> > > > > PCIBIOS_MIN_MEM;
> > > > 
> > > > I don't understand the connection here.  PCIBIOS_MIN_MEM and
> > > > PCIBIOS_MIN_IO are basically ways to say "we can't put PCI
> > > > resources below this address".
> > > > 
> > > > On ACPI systems, the devices in the ACPI namespace are
> > > > supposed to tell the OS what resources they use, and obviously
> > > > the OS should not assign those resources to anything else.  If
> > > > Linux handled all those ACPI resources correctly and in the
> > > > absence of firmware defects, we shouldn't need
> > > > PCIBIOS_MIN_MEM/_IO at all.  But neither of those is currently
> > > > true.
> > > > 
> > > > It's true that we should be smarter about PCIBIOS_MIN_MEM/_IO,
> > > > but I don't think that has anything to do with whether we
> > > > support *moving* BARs.  We have to avoid the address space
> > > > that's already in use in *all* cases.
> > > 
> > > This is connected to the approach of this feature: releasing,
> > > recalculating and reassigning the BARs and bridge windows. If
> > > movable BARs are disabled, this bug doesn't reproduce. And the
> > > bug doesn't let the system boot when BARs are allowed to move.
> > > That's why I've tied these together.
> > 
> > My point is just that logically this has nothing to do with
> > movable BARs.
> > 
> > > This line setting the "min" to PCIBIOS_MIN_* is there untouched
> > > since the first kernel git commit in 2005 - could it be that all
> > > systems are just fine now, having their root bridge windows set
> > > up correctly?
> > 
> > I don't understand the question, sorry.
> 
> I mean, every BAR assigned here can't reside outside of a host
> IO/MEM bridge window, which is a bus->resource[n] set up by the
> platform code, and their .start fields are seemed to be duplicated
> by the PCIBIOS_MIN_* values - from the platform code as well. But
> the .start fields are seem to be correct (aren't they?), and the
> PCIBIOS_MIN_* values are sometimes definitely not.
> 
> What can be a reliable test to check if PCIBIOS_MIN_* are safe to
> ignore unconditionally? Could it be a separate flag instead of the
> pci_can_move_bars here?
> 
> Would it be fine for a start to ignore the PCIBIOS_MIN_* if it lies
> completely outside of host bridge windows? So at least AMD EPYC can
> obtain its hotplug power.

PCIBIOS_MIN_* has a long history and it touches every arch, so you'd
have to make sure this is safe for all of them.

On x86, PCIBIOS_MIN_MEM is computed from the e820 memory map and is
basically a guess because the e820 map is only incidentally related to
ACPI device resource usage.  I could imagine making the x86
computation smarter by looking at the PNP0A03/PNP0A08 _CRS
information.

> > > > >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > > > > PCI_BRIDGE_RESOURCES) {
> > > > >  		struct pci_bus *child_bus = dev->subordinate;
> > > > > -- 
> > > > > 2.24.1
> > > > >
Sergei Miroshnichenko Feb. 12, 2020, 12:16 p.m. UTC | #6
On Wed, 2020-02-05 at 10:32 -0600, Bjorn Helgaas wrote:
> On Wed, Feb 05, 2020 at 01:04:06PM +0000, Sergei Miroshnichenko
> wrote:
> > On Fri, 2020-01-31 at 14:27 -0600, Bjorn Helgaas wrote:
> > > On Fri, Jan 31, 2020 at 06:19:48PM +0000, Sergei Miroshnichenko
> > > wrote:
> > > > On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> > > > > On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei
> > > > > Miroshnichenko
> > > > > wrote:
> > > > > > BARs and bridge windows are only allowed to be assigned to
> > > > > > their parent bus's bridge windows, going up to the root
> > > > > > complex's resources.  So additional limitations on BAR
> > > > > > address are not needed, and the PCIBIOS_MIN_MEM can be
> > > > > > ignored.
> > > > > 
> > > > > This is theoretically true, but I don't think we have
> > > > > reliable
> > > > > information about the host bridge windows in all cases, so
> > > > > PCIBIOS_MIN_MEM/_IO is something of an approximation.
> > > > > 
> > > > > > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS
> > > > > > 1.3 on Supermicro H11SSL-i via e820__setup_pci_gap():
> > > > > > 
> > > > > >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > > > > > 
> > > > > > is only suitable for a single RC out of four:
> > > > > > 
> > > > > >   pci_bus 0000:00: root bus resource [mem 0xec000000-
> > > > > > 0xefffffff
> > > > > > window]
> > > > > >   pci_bus 0000:20: root bus resource [mem 0xeb800000-
> > > > > > 0xebefffff
> > > > > > window]
> > > > > >   pci_bus 0000:40: root bus resource [mem 0xeb200000-
> > > > > > 0xeb5fffff
> > > > > > window]
> > > > > >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-
> > > > > > 0xeaffffff
> > > > > > window]
> > > > > > 
> > > > > > , which makes the AMD EPYC 7251 unable to boot with this
> > > > > > movable BARs patchset.
> > > > > 
> > > > > Something's wrong if this system booted before this patch set
> > > > > but not after.  We shouldn't be doing *anything* with the
> > > > > BARs
> > > > > until we need to, i.e., until we hot-add a device where we
> > > > > have to move things to find space for it.
> > > > 
> > > > The one breaking boot on this system initially was 17/26 of
> > > > this
> > > > patchset: "PCI: hotplug: Ignore the MEM BAR offsets from
> > > > BIOS/bootloader"
> > > 
> > > I don't think that patch is a good idea.  I think we should read
> > > the
> > > current BARs and windows at boot-time and leave them alone unless
> > > we
> > > *must* change them.  I don't think we should change things
> > > preemptively to make future hotplug events easier.
> > > 
> > > > Before it the kernel just took BARs pre-assigned by BIOS. In
> > > > the
> > > > same time, the same BIOS reports 0xebff1000-0xfe9fffff as
> > > > available for PCI devices, but the real root bridge windows are
> > > > 0xe8b00000-0xefffffff in total (and also 64-bit windows) -
> > > > which
> > > > are also reported by the same BIOS. So the kernel was only able
> > > > to handle the 0xec000000- 0xefffffff root bus.
> > > > 
> > > > With that patch reverted the kernel was able to boot, but
> > > > unable to
> > > > rescan - to reassign BARs actually.
> > > > 
> > > > > (And we don't want a bisection hole where this system can't
> > > > > boot until this patch is applied, but I assume that's
> > > > > obvious.)
> > > > > 
> > > > > > Signed-off-by: Sergei Miroshnichenko <
> > > > > > s.miroshnichenko@yadro.com>
> > > > > > ---
> > > > > >  drivers/pci/setup-res.c | 5 +++--
> > > > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-
> > > > > > res.c
> > > > > > index a7d81816d1ea..4043aab021dd 100644
> > > > > > --- a/drivers/pci/setup-res.c
> > > > > > +++ b/drivers/pci/setup-res.c
> > > > > > @@ -246,12 +246,13 @@ static int
> > > > > > __pci_assign_resource(struct
> > > > > > pci_bus *bus, struct pci_dev *dev,
> > > > > >  		int resno, resource_size_t size,
> > > > > > resource_size_t align)
> > > > > >  {
> > > > > >  	struct resource *res = dev->resource + resno;
> > > > > > -	resource_size_t min;
> > > > > > +	resource_size_t min = 0;
> > > > > >  	int ret;
> > > > > >  	resource_size_t start = (resource_size_t)-1;
> > > > > >  	resource_size_t end = 0;
> > > > > >  
> > > > > > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > > > > PCIBIOS_MIN_MEM;
> > > > > > +	if (!pci_can_move_bars)
> > > > > > +		min = (res->flags & IORESOURCE_IO) ?
> > > > > > PCIBIOS_MIN_IO :
> > > > > > PCIBIOS_MIN_MEM;
> > > > > 
> > > > > I don't understand the connection here.  PCIBIOS_MIN_MEM and
> > > > > PCIBIOS_MIN_IO are basically ways to say "we can't put PCI
> > > > > resources below this address".
> > > > > 
> > > > > On ACPI systems, the devices in the ACPI namespace are
> > > > > supposed to tell the OS what resources they use, and
> > > > > obviously
> > > > > the OS should not assign those resources to anything
> > > > > else.  If
> > > > > Linux handled all those ACPI resources correctly and in the
> > > > > absence of firmware defects, we shouldn't need
> > > > > PCIBIOS_MIN_MEM/_IO at all.  But neither of those is
> > > > > currently
> > > > > true.
> > > > > 
> > > > > It's true that we should be smarter about
> > > > > PCIBIOS_MIN_MEM/_IO,
> > > > > but I don't think that has anything to do with whether we
> > > > > support *moving* BARs.  We have to avoid the address space
> > > > > that's already in use in *all* cases.
> > > > 
> > > > This is connected to the approach of this feature: releasing,
> > > > recalculating and reassigning the BARs and bridge windows. If
> > > > movable BARs are disabled, this bug doesn't reproduce. And the
> > > > bug doesn't let the system boot when BARs are allowed to move.
> > > > That's why I've tied these together.
> > > 
> > > My point is just that logically this has nothing to do with
> > > movable BARs.
> > > 
> > > > This line setting the "min" to PCIBIOS_MIN_* is there untouched
> > > > since the first kernel git commit in 2005 - could it be that
> > > > all
> > > > systems are just fine now, having their root bridge windows set
> > > > up correctly?
> > > 
> > > I don't understand the question, sorry.
> > 
> > I mean, every BAR assigned here can't reside outside of a host
> > IO/MEM bridge window, which is a bus->resource[n] set up by the
> > platform code, and their .start fields are seemed to be duplicated
> > by the PCIBIOS_MIN_* values - from the platform code as well. But
> > the .start fields are seem to be correct (aren't they?), and the
> > PCIBIOS_MIN_* values are sometimes definitely not.
> > 
> > What can be a reliable test to check if PCIBIOS_MIN_* are safe to
> > ignore unconditionally? Could it be a separate flag instead of the
> > pci_can_move_bars here?
> > 
> > Would it be fine for a start to ignore the PCIBIOS_MIN_* if it lies
> > completely outside of host bridge windows? So at least AMD EPYC can
> > obtain its hotplug power.
> 
> PCIBIOS_MIN_* has a long history and it touches every arch, so you'd
> have to make sure this is safe for all of them.
> 

Right, I should rework this change and make it x86-specific - the only
platform where I've encountered this issue (invalid PCIBIOS_MIN_MEM
from the e820 memory map, preventing hotplug).

> On x86, PCIBIOS_MIN_MEM is computed from the e820 memory map and is
> basically a guess because the e820 map is only incidentally related
> to
> ACPI device resource usage.  I could imagine making the x86
> computation smarter by looking at the PNP0A03/PNP0A08 _CRS
> information.
> 

Would it be acceptable to set PCIBIOS_MIN_MEM to zero for x86 in
arch/x86/include/asm/pci.h ? I've debugged PCs in my possession, and I
see there every ACPI_RESOURCE_TYPE_ADDRESS* and
ACPI_RESOURCE_TYPE_FIXED_MEMORY* resource extracted from the ACPI are
eventually represented in /proc/iomem and /proc/ioports, so the kernel
can't put device BARs in these reserved address ranges.

Thanks,
Serge

> > > > > >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > > > > > PCI_BRIDGE_RESOURCES) {
> > > > > >  		struct pci_bus *child_bus = dev->subordinate;
> > > > > > -- 
> > > > > > 2.24.1
> > > > > >
Bjorn Helgaas Feb. 12, 2020, 2:13 p.m. UTC | #7
On Wed, Feb 12, 2020 at 12:16:55PM +0000, Sergei Miroshnichenko wrote:
> On Wed, 2020-02-05 at 10:32 -0600, Bjorn Helgaas wrote:
> > On Wed, Feb 05, 2020 at 01:04:06PM +0000, Sergei Miroshnichenko
> > wrote:
> > > On Fri, 2020-01-31 at 14:27 -0600, Bjorn Helgaas wrote:
> > > > On Fri, Jan 31, 2020 at 06:19:48PM +0000, Sergei Miroshnichenko
> > > > wrote:
> > > > > On Thu, 2020-01-30 at 17:52 -0600, Bjorn Helgaas wrote:
> > > > > > On Wed, Jan 29, 2020 at 06:29:27PM +0300, Sergei
> > > > > > Miroshnichenko
> > > > > > wrote:
> > > > > > > BARs and bridge windows are only allowed to be assigned to
> > > > > > > their parent bus's bridge windows, going up to the root
> > > > > > > complex's resources.  So additional limitations on BAR
> > > > > > > address are not needed, and the PCIBIOS_MIN_MEM can be
> > > > > > > ignored.
> > > > > > 
> > > > > > This is theoretically true, but I don't think we have
> > > > > > reliable
> > > > > > information about the host bridge windows in all cases, so
> > > > > > PCIBIOS_MIN_MEM/_IO is something of an approximation.
> > > > > > 
> > > > > > > Besides, the value of PCIBIOS_MIN_MEM reported by the BIOS
> > > > > > > 1.3 on Supermicro H11SSL-i via e820__setup_pci_gap():
> > > > > > > 
> > > > > > >   [mem 0xebff1000-0xfe9fffff] available for PCI devices
> > > > > > > 
> > > > > > > is only suitable for a single RC out of four:
> > > > > > > 
> > > > > > >   pci_bus 0000:00: root bus resource [mem 0xec000000-
> > > > > > > 0xefffffff
> > > > > > > window]
> > > > > > >   pci_bus 0000:20: root bus resource [mem 0xeb800000-
> > > > > > > 0xebefffff
> > > > > > > window]
> > > > > > >   pci_bus 0000:40: root bus resource [mem 0xeb200000-
> > > > > > > 0xeb5fffff
> > > > > > > window]
> > > > > > >   pci_bus 0000:60: root bus resource [mem 0xe8b00000-
> > > > > > > 0xeaffffff
> > > > > > > window]
> > > > > > > 
> > > > > > > , which makes the AMD EPYC 7251 unable to boot with this
> > > > > > > movable BARs patchset.
> > > > > > 
> > > > > > Something's wrong if this system booted before this patch
> > > > > > set but not after.  We shouldn't be doing *anything* with
> > > > > > the BARs until we need to, i.e., until we hot-add a device
> > > > > > where we have to move things to find space for it.
> > > > > 
> > > > > The one breaking boot on this system initially was 17/26 of
> > > > > this patchset: "PCI: hotplug: Ignore the MEM BAR offsets
> > > > > from BIOS/bootloader"
> > > > 
> > > > I don't think that patch is a good idea.  I think we should
> > > > read the current BARs and windows at boot-time and leave them
> > > > alone unless we *must* change them.  I don't think we should
> > > > change things preemptively to make future hotplug events
> > > > easier.
> > > > 
> > > > > Before it the kernel just took BARs pre-assigned by BIOS. In
> > > > > the same time, the same BIOS reports 0xebff1000-0xfe9fffff
> > > > > as available for PCI devices, but the real root bridge
> > > > > windows are 0xe8b00000-0xefffffff in total (and also 64-bit
> > > > > windows) - which are also reported by the same BIOS. So the
> > > > > kernel was only able to handle the 0xec000000- 0xefffffff
> > > > > root bus.
> > > > > 
> > > > > With that patch reverted the kernel was able to boot, but
> > > > > unable to rescan - to reassign BARs actually.
> > > > > 
> > > > > > (And we don't want a bisection hole where this system can't
> > > > > > boot until this patch is applied, but I assume that's
> > > > > > obvious.)
> > > > > > 
> > > > > > > Signed-off-by: Sergei Miroshnichenko <
> > > > > > > s.miroshnichenko@yadro.com>
> > > > > > > ---
> > > > > > >  drivers/pci/setup-res.c | 5 +++--
> > > > > > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-
> > > > > > > res.c
> > > > > > > index a7d81816d1ea..4043aab021dd 100644
> > > > > > > --- a/drivers/pci/setup-res.c
> > > > > > > +++ b/drivers/pci/setup-res.c
> > > > > > > @@ -246,12 +246,13 @@ static int
> > > > > > > __pci_assign_resource(struct
> > > > > > > pci_bus *bus, struct pci_dev *dev,
> > > > > > >  		int resno, resource_size_t size,
> > > > > > > resource_size_t align)
> > > > > > >  {
> > > > > > >  	struct resource *res = dev->resource + resno;
> > > > > > > -	resource_size_t min;
> > > > > > > +	resource_size_t min = 0;
> > > > > > >  	int ret;
> > > > > > >  	resource_size_t start = (resource_size_t)-1;
> > > > > > >  	resource_size_t end = 0;
> > > > > > >  
> > > > > > > -	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO :
> > > > > > > PCIBIOS_MIN_MEM;
> > > > > > > +	if (!pci_can_move_bars)
> > > > > > > +		min = (res->flags & IORESOURCE_IO) ?
> > > > > > > PCIBIOS_MIN_IO :
> > > > > > > PCIBIOS_MIN_MEM;
> > > > > > 
> > > > > > I don't understand the connection here.  PCIBIOS_MIN_MEM and
> > > > > > PCIBIOS_MIN_IO are basically ways to say "we can't put PCI
> > > > > > resources below this address".
> > > > > > 
> > > > > > On ACPI systems, the devices in the ACPI namespace are
> > > > > > supposed to tell the OS what resources they use, and
> > > > > > obviously
> > > > > > the OS should not assign those resources to anything
> > > > > > else.  If
> > > > > > Linux handled all those ACPI resources correctly and in the
> > > > > > absence of firmware defects, we shouldn't need
> > > > > > PCIBIOS_MIN_MEM/_IO at all.  But neither of those is
> > > > > > currently
> > > > > > true.
> > > > > > 
> > > > > > It's true that we should be smarter about
> > > > > > PCIBIOS_MIN_MEM/_IO,
> > > > > > but I don't think that has anything to do with whether we
> > > > > > support *moving* BARs.  We have to avoid the address space
> > > > > > that's already in use in *all* cases.
> > > > > 
> > > > > This is connected to the approach of this feature: releasing,
> > > > > recalculating and reassigning the BARs and bridge windows. If
> > > > > movable BARs are disabled, this bug doesn't reproduce. And the
> > > > > bug doesn't let the system boot when BARs are allowed to move.
> > > > > That's why I've tied these together.
> > > > 
> > > > My point is just that logically this has nothing to do with
> > > > movable BARs.
> > > > 
> > > > > This line setting the "min" to PCIBIOS_MIN_* is there untouched
> > > > > since the first kernel git commit in 2005 - could it be that
> > > > > all
> > > > > systems are just fine now, having their root bridge windows set
> > > > > up correctly?
> > > > 
> > > > I don't understand the question, sorry.
> > > 
> > > I mean, every BAR assigned here can't reside outside of a host
> > > IO/MEM bridge window, which is a bus->resource[n] set up by the
> > > platform code, and their .start fields are seemed to be duplicated
> > > by the PCIBIOS_MIN_* values - from the platform code as well. But
> > > the .start fields are seem to be correct (aren't they?), and the
> > > PCIBIOS_MIN_* values are sometimes definitely not.
> > > 
> > > What can be a reliable test to check if PCIBIOS_MIN_* are safe to
> > > ignore unconditionally? Could it be a separate flag instead of the
> > > pci_can_move_bars here?
> > > 
> > > Would it be fine for a start to ignore the PCIBIOS_MIN_* if it lies
> > > completely outside of host bridge windows? So at least AMD EPYC can
> > > obtain its hotplug power.
> > 
> > PCIBIOS_MIN_* has a long history and it touches every arch, so you'd
> > have to make sure this is safe for all of them.
> 
> Right, I should rework this change and make it x86-specific - the
> only platform where I've encountered this issue (invalid
> PCIBIOS_MIN_MEM from the e820 memory map, preventing hotplug).
> 
> > On x86, PCIBIOS_MIN_MEM is computed from the e820 memory map and
> > is basically a guess because the e820 map is only incidentally
> > related to ACPI device resource usage.  I could imagine making the
> > x86 computation smarter by looking at the PNP0A03/PNP0A08 _CRS
> > information.
> 
> Would it be acceptable to set PCIBIOS_MIN_MEM to zero for x86 in
> arch/x86/include/asm/pci.h ? I've debugged PCs in my possession, and
> I see there every ACPI_RESOURCE_TYPE_ADDRESS* and
> ACPI_RESOURCE_TYPE_FIXED_MEMORY* resource extracted from the ACPI
> are eventually represented in /proc/iomem and /proc/ioports, so the
> kernel can't put device BARs in these reserved address ranges.

I think setting PCIBIOS_MIN_MEM to zero for all of x86 would be too
hard to validate.  On x86, PCIBIOS_MIN_MEM is actually a variable
(pci_mem_start), so you could adjust that as we process host bridge
_CRS methods, e.g., if you find an aperture that starts below
pci_mem_start, update pci_mem_start to the beginning of the aperture.

> > > > > > >  	if (pci_can_move_bars && dev->subordinate && resno >=
> > > > > > > PCI_BRIDGE_RESOURCES) {
> > > > > > >  		struct pci_bus *child_bus = dev->subordinate;
> > > > > > > -- 
> > > > > > > 2.24.1
> > > > > > >
diff mbox series

Patch

diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index a7d81816d1ea..4043aab021dd 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -246,12 +246,13 @@  static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
 		int resno, resource_size_t size, resource_size_t align)
 {
 	struct resource *res = dev->resource + resno;
-	resource_size_t min;
+	resource_size_t min = 0;
 	int ret;
 	resource_size_t start = (resource_size_t)-1;
 	resource_size_t end = 0;
 
-	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
+	if (!pci_can_move_bars)
+		min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
 
 	if (pci_can_move_bars && dev->subordinate && resno >= PCI_BRIDGE_RESOURCES) {
 		struct pci_bus *child_bus = dev->subordinate;