Patchwork [v2,4/5] ACPI/PCI: Warn if we have to "guess" host bridge node information

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Submitter Myron Stowe
Date April 19, 2014, 2:53 a.m.
Message ID <20140419025339.2408.17866.stgit@amt.stowe>
Download mbox | patch
Permalink /patch/340455/
State Changes Requested
Headers show

Comments

Myron Stowe - April 19, 2014, 2:53 a.m.
The vast majority of platforms are not supplying ACPI _PXM (proximity)
information corresponding to host bridge (PNP0A03/PNP0A08) devices
resulting in sysfs "numa_node" values of -1 (NUMA_NO_NODE) [1]:
  # for i in /sys/devices/pci0000\:00/*/numa_node; do cat $i; done | uniq
  -1

  # find /sys/ -name "numa_node" | while read fname; do cat $fname; \
    done | uniq
  -1

AMD based platforms provide a fall-back for this situation via amd_bus.c.
These platforms snoop out the information by directly reading specific
registers from the Northbridge and caching them via 'alloc_pci_root_info'.

Later during boot processing when host bridges are discovered -
'pci_acpi_scan_root' - the kernel looks for their corresponding ACPI _PXM
method - drivers/acpi/numa.c::acpi_get_node().  If the BIOS supplied a
_PXM method then that node (proximity) value is associated.  If the BIOS
did not supply a _PXM method *and* the platform is AMD based, the
fall-back cached values obtained directly from the Northbridge are used;
otherwise, "NUMA_NO_NODE" is associated.

There are a number of issues with this fall-back mechanism the most
notable being that amd_bus.c extracts a 3-bit number from a CPU register
and uses it as the node number.  The node numbers used by Linux are
logical and there's no reason they need to be identical to settings in the
CPU registers.  So if we have some node information obtained in the normal
way (from _PXM, SLIT, SRAT, etc.) and some from amd_bus.c, there's no
reason to believe they will be compatible.

This patch warns when this situation occurs:
  pci_root PNP0A08:00: [Firmware Bug]: No _PXM; guessing node number 0

[1] https://bugzilla.kernel.org/show_bug.cgi?id=72051

Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
---

 arch/x86/pci/acpi.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)


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Borislav Petkov - April 20, 2014, 10:21 a.m.
On Fri, Apr 18, 2014 at 08:53:39PM -0600, Myron Stowe wrote:
> The vast majority of platforms are not supplying ACPI _PXM (proximity)
> information corresponding to host bridge (PNP0A03/PNP0A08) devices
> resulting in sysfs "numa_node" values of -1 (NUMA_NO_NODE) [1]:
>   # for i in /sys/devices/pci0000\:00/*/numa_node; do cat $i; done | uniq
>   -1
> 
>   # find /sys/ -name "numa_node" | while read fname; do cat $fname; \
>     done | uniq
>   -1
> 
> AMD based platforms provide a fall-back for this situation via amd_bus.c.
> These platforms snoop out the information by directly reading specific
> registers from the Northbridge and caching them via 'alloc_pci_root_info'.
> 
> Later during boot processing when host bridges are discovered -
> 'pci_acpi_scan_root' - the kernel looks for their corresponding ACPI _PXM
> method - drivers/acpi/numa.c::acpi_get_node().  If the BIOS supplied a
> _PXM method then that node (proximity) value is associated.  If the BIOS
> did not supply a _PXM method *and* the platform is AMD based, the
> fall-back cached values obtained directly from the Northbridge are used;
> otherwise, "NUMA_NO_NODE" is associated.
> 
> There are a number of issues with this fall-back mechanism the most
> notable being that amd_bus.c extracts a 3-bit number from a CPU register
> and uses it as the node number.  The node numbers used by Linux are
> logical and there's no reason they need to be identical to settings in the
> CPU registers.  So if we have some node information obtained in the normal
> way (from _PXM, SLIT, SRAT, etc.) and some from amd_bus.c, there's no
> reason to believe they will be compatible.
> 
> This patch warns when this situation occurs:
>   pci_root PNP0A08:00: [Firmware Bug]: No _PXM; guessing node number 0
> 
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=72051
> 
> Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
> ---
> 
>  arch/x86/pci/acpi.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
> index 01edac6..80c09ba 100644
> --- a/arch/x86/pci/acpi.c
> +++ b/arch/x86/pci/acpi.c
> @@ -489,8 +489,12 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
>  	}
>  
>  	node = acpi_get_node(device->handle);
> -	if (node == NUMA_NO_NODE)
> +	if (node == NUMA_NO_NODE) {
>  		node = x86_pci_root_bus_node(busnum);
> +		if (node != NUMA_NO_NODE)
> +			dev_info(&device->dev, FW_BUG "No _PXM; guessing node number %x\n",

Hmm, I'm not really convinced this message is user-friendly enough. Can
we be more descriptive here please?
Myron Stowe - April 28, 2014, 9:24 p.m.
On Sun, Apr 20, 2014 at 4:21 AM, Borislav Petkov <bp@suse.de> wrote:
> On Fri, Apr 18, 2014 at 08:53:39PM -0600, Myron Stowe wrote:
>> The vast majority of platforms are not supplying ACPI _PXM (proximity)
>> information corresponding to host bridge (PNP0A03/PNP0A08) devices
>> resulting in sysfs "numa_node" values of -1 (NUMA_NO_NODE) [1]:
>>   # for i in /sys/devices/pci0000\:00/*/numa_node; do cat $i; done | uniq
>>   -1
>>
>>   # find /sys/ -name "numa_node" | while read fname; do cat $fname; \
>>     done | uniq
>>   -1
>>
>> AMD based platforms provide a fall-back for this situation via amd_bus.c.
>> These platforms snoop out the information by directly reading specific
>> registers from the Northbridge and caching them via 'alloc_pci_root_info'.
>>
>> Later during boot processing when host bridges are discovered -
>> 'pci_acpi_scan_root' - the kernel looks for their corresponding ACPI _PXM
>> method - drivers/acpi/numa.c::acpi_get_node().  If the BIOS supplied a
>> _PXM method then that node (proximity) value is associated.  If the BIOS
>> did not supply a _PXM method *and* the platform is AMD based, the
>> fall-back cached values obtained directly from the Northbridge are used;
>> otherwise, "NUMA_NO_NODE" is associated.
>>
>> There are a number of issues with this fall-back mechanism the most
>> notable being that amd_bus.c extracts a 3-bit number from a CPU register
>> and uses it as the node number.  The node numbers used by Linux are
>> logical and there's no reason they need to be identical to settings in the
>> CPU registers.  So if we have some node information obtained in the normal
>> way (from _PXM, SLIT, SRAT, etc.) and some from amd_bus.c, there's no
>> reason to believe they will be compatible.
>>
>> This patch warns when this situation occurs:
>>   pci_root PNP0A08:00: [Firmware Bug]: No _PXM; guessing node number 0
>>
>> [1] https://bugzilla.kernel.org/show_bug.cgi?id=72051
>>
>> Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
>> ---
>>
>>  arch/x86/pci/acpi.c |    6 +++++-
>>  1 files changed, 5 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
>> index 01edac6..80c09ba 100644
>> --- a/arch/x86/pci/acpi.c
>> +++ b/arch/x86/pci/acpi.c
>> @@ -489,8 +489,12 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
>>       }
>>
>>       node = acpi_get_node(device->handle);
>> -     if (node == NUMA_NO_NODE)
>> +     if (node == NUMA_NO_NODE) {
>>               node = x86_pci_root_bus_node(busnum);
>> +             if (node != NUMA_NO_NODE)
>> +                     dev_info(&device->dev, FW_BUG "No _PXM; guessing node number %x\n",
>
> Hmm, I'm not really convinced this message is user-friendly enough. Can
> we be more descriptive here please?
>

How about -
  dev_info(&device->dev, FW_BUG "no _PXM; falling back to node %d from
hardware (may be inconsistent with ACPI node numbers)\n", node);

> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --
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> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
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Borislav Petkov - April 29, 2014, 7:16 p.m.
On Mon, Apr 28, 2014 at 03:24:39PM -0600, Myron Stowe wrote:
> >> @@ -489,8 +489,12 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> >>       }
> >>
> >>       node = acpi_get_node(device->handle);
> >> -     if (node == NUMA_NO_NODE)
> >> +     if (node == NUMA_NO_NODE) {
> >>               node = x86_pci_root_bus_node(busnum);
> >> +             if (node != NUMA_NO_NODE)
> >> +                     dev_info(&device->dev, FW_BUG "No _PXM; guessing node number %x\n",
> >
> > Hmm, I'm not really convinced this message is user-friendly enough. Can
> > we be more descriptive here please?
> >
> 
> How about -
>   dev_info(&device->dev, FW_BUG "no _PXM; falling back to node %d from
> hardware (may be inconsistent with ACPI node numbers)\n", node);

Yep, better.

Patch

diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 01edac6..80c09ba 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -489,8 +489,12 @@  struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 	}
 
 	node = acpi_get_node(device->handle);
-	if (node == NUMA_NO_NODE)
+	if (node == NUMA_NO_NODE) {
 		node = x86_pci_root_bus_node(busnum);
+		if (node != NUMA_NO_NODE)
+			dev_info(&device->dev, FW_BUG "No _PXM; guessing node number %x\n",
+				node);
+	}
 
 	if (node != NUMA_NO_NODE && !node_online(node))
 		node = NUMA_NO_NODE;