| Message ID | 20171031040427.10909-1-aik@ozlabs.ru (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | [kernel] powerpc/powernv/ioda: Relax max DMA window size check | expand |
On 31/10/17 15:04, Alexey Kardashevskiy wrote: > DMA windows can only have a size of power of two on IODA2 hardware and > using memory_hotplug_max() to determine the upper limit won't work > correcly if it returns not power of two value. > > This relaxes the check by rounding up the value returned by > memory_hotplug_max(). > > It is expected to impact DPDK on machines with non-power-of-two RAM size, > mostly. KVM guests are less likely to be affected as usually guests get > less than half of hosts RAM. It was pointed out that this check is quite useless anyway as the vm_locked memory limit should hit first, and if that is not set or the user got the root privilege level, then there are easier ways to crash the host so I am thinking of: diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c index 269f119e4b3c..a47e4cf343b2 100644 --- a/arch/powerpc/platforms/powernv/pci-ioda.c +++ b/arch/powerpc/platforms/powernv/pci-ioda.c @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset, if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) return -EINVAL; - if ((window_size > memory_hotplug_max()) || !is_power_of_2(window_size)) + if (!is_power_of_2(window_size)) return -EINVAL; Makes sense? > > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> > --- > arch/powerpc/platforms/powernv/pci-ioda.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c > index 269f119e4b3c..4c62162da181 100644 > --- a/arch/powerpc/platforms/powernv/pci-ioda.c > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c > @@ -2769,7 +2769,8 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset, > if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) > return -EINVAL; > > - if ((window_size > memory_hotplug_max()) || !is_power_of_2(window_size)) > + if ((window_size > roundup_pow_of_two(memory_hotplug_max())) || > + !is_power_of_2(window_size)) > return -EINVAL; > > /* Adjust direct table size from window_size and levels */ >
Alexey Kardashevskiy <aik@ozlabs.ru> writes: > On 31/10/17 15:04, Alexey Kardashevskiy wrote: >> DMA windows can only have a size of power of two on IODA2 hardware and >> using memory_hotplug_max() to determine the upper limit won't work >> correcly if it returns not power of two value. >> >> This relaxes the check by rounding up the value returned by >> memory_hotplug_max(). >> >> It is expected to impact DPDK on machines with non-power-of-two RAM size, >> mostly. KVM guests are less likely to be affected as usually guests get >> less than half of hosts RAM. > > > It was pointed out that this check is quite useless anyway as the vm_locked > memory limit should hit first, and if that is not set or the user got the > root privilege level, then there are easier ways to crash the host so I am > thinking of: > > > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c > b/arch/powerpc/platforms/powernv/pci-ioda.c > index 269f119e4b3c..a47e4cf343b2 100644 > --- a/arch/powerpc/platforms/powernv/pci-ioda.c > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c > @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, > __u64 bus_offset, > if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) > return -EINVAL; > > - if ((window_size > memory_hotplug_max()) || > !is_power_of_2(window_size)) > + if (!is_power_of_2(window_size)) > return -EINVAL; > > > > Makes sense? Sounds reasonable. Execpt where is the vm_locked check? I think it's in the VFIO driver? If so I guess the only concern is that this code might be called via some other path that doesn't do that check. cheers
Michael Ellerman <mpe@ellerman.id.au> wrote on 11/06/2017 11:45:34 AM: > From: Michael Ellerman <mpe@ellerman.id.au> > To: Alexey Kardashevskiy <aik@ozlabs.ru>, David Gibson > <david@gibson.dropbear.id.au> > Cc: linuxppc-dev@lists.ozlabs.org, Jonas Pfefferle1 > <JPF@zurich.ibm.com>, Nicholas Piggin <npiggin@gmail.com> > Date: 11/06/2017 11:45 AM > Subject: Re: [PATCH kernel] powerpc/powernv/ioda: Relax max DMA > window size check > > Alexey Kardashevskiy <aik@ozlabs.ru> writes: > > > On 31/10/17 15:04, Alexey Kardashevskiy wrote: > >> DMA windows can only have a size of power of two on IODA2 hardware and > >> using memory_hotplug_max() to determine the upper limit won't work > >> correcly if it returns not power of two value. > >> > >> This relaxes the check by rounding up the value returned by > >> memory_hotplug_max(). > >> > >> It is expected to impact DPDK on machines with non-power-of-two RAM size, > >> mostly. KVM guests are less likely to be affected as usually guests get > >> less than half of hosts RAM. > > > > > > It was pointed out that this check is quite useless anyway as the vm_locked > > memory limit should hit first, and if that is not set or the user got the > > root privilege level, then there are easier ways to crash the host so I am > > thinking of: > > > > > > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c > > b/arch/powerpc/platforms/powernv/pci-ioda.c > > index 269f119e4b3c..a47e4cf343b2 100644 > > --- a/arch/powerpc/platforms/powernv/pci-ioda.c > > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c > > @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, > > __u64 bus_offset, > > if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) > > return -EINVAL; > > > > - if ((window_size > memory_hotplug_max()) || > > !is_power_of_2(window_size)) > > + if (!is_power_of_2(window_size)) > > return -EINVAL; > > > > > > > > Makes sense? > > Sounds reasonable. > > Execpt where is the vm_locked check? I think it's in the VFIO driver? If > so I guess the only concern is that this code might be called via some > other path that doesn't do that check. > > cheers > The vm_locked is incremented here: http://elixir.free-electrons.com/linux/v4.13.11/source/drivers/vfio/vfio_iommu_spapr_tce.c#L176 resp. http://elixir.free-electrons.com/linux/v4.13.11/source/arch/powerpc/mm/mmu_context_iommu.c#L124 on VFIO_IOMMU_SPAPR_REGISTER_MEMORY. From my understanding only pages that have been registered through here can be mapped with MAP_DMA. Cheers, Jonas <html><body><p><tt><font size="2">Michael Ellerman <mpe@ellerman.id.au> wrote on 11/06/2017 11:45:34 AM:<br><br>> From: Michael Ellerman <mpe@ellerman.id.au></font></tt><br><tt><font size="2">> To: Alexey Kardashevskiy <aik@ozlabs.ru>, David Gibson <br>> <david@gibson.dropbear.id.au></font></tt><br><tt><font size="2">> Cc: linuxppc-dev@lists.ozlabs.org, Jonas Pfefferle1 <br>> <JPF@zurich.ibm.com>, Nicholas Piggin <npiggin@gmail.com></font></tt><br><tt><font size="2">> Date: 11/06/2017 11:45 AM</font></tt><br><tt><font size="2">> Subject: Re: [PATCH kernel] powerpc/powernv/ioda: Relax max DMA <br>> window size check</font></tt><br><tt><font size="2">> <br>> Alexey Kardashevskiy <aik@ozlabs.ru> writes:<br>> <br>> > On 31/10/17 15:04, Alexey Kardashevskiy wrote:<br>> >> DMA windows can only have a size of power of two on IODA2 hardware and<br>> >> using memory_hotplug_max() to determine the upper limit won't work<br>> >> correcly if it returns not power of two value.<br>> >> <br>> >> This relaxes the check by rounding up the value returned by<br>> >> memory_hotplug_max().<br>> >> <br>> >> It is expected to impact DPDK on machines with non-power-of-two RAM size,<br>> >> mostly. KVM guests are less likely to be affected as usually guests get<br>> >> less than half of hosts RAM.<br>> ><br>> ><br>> > It was pointed out that this check is quite useless anyway as the vm_locked<br>> > memory limit should hit first, and if that is not set or the user got the<br>> > root privilege level, then there are easier ways to crash the host so I am<br>> > thinking of:<br>> ><br>> ><br>> > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c<br>> > b/arch/powerpc/platforms/powernv/pci-ioda.c<br>> > index 269f119e4b3c..a47e4cf343b2 100644<br>> > --- a/arch/powerpc/platforms/powernv/pci-ioda.c<br>> > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c<br>> > @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid,<br>> > __u64 bus_offset,<br>> > if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS))<br>> > return -EINVAL;<br>> ><br>> > - if ((window_size > memory_hotplug_max()) ||<br>> > !is_power_of_2(window_size))<br>> > + if (!is_power_of_2(window_size))<br>> > return -EINVAL;<br>> ><br>> ><br>> ><br>> > Makes sense?<br>> <br>> Sounds reasonable.<br>> <br>> Execpt where is the vm_locked check? I think it's in the VFIO driver? If<br>> so I guess the only concern is that this code might be called via some<br>> other path that doesn't do that check.<br>> <br>> cheers<br>> </font></tt><br><br><tt><font size="2">The vm_locked is incremented here:</font></tt><br><a href="http://elixir.free-electrons.com/linux/v4.13.11/source/drivers/vfio/vfio_iommu_spapr_tce.c#L176"><tt><font size="2">http://elixir.free-electrons.com/linux/v4.13.11/source/drivers/vfio/vfio_iommu_spapr_tce.c#L176</font></tt></a><br><tt><font size="2">resp. </font></tt><a href="http://elixir.free-electrons.com/linux/v4.13.11/source/arch/powerpc/mm/mmu_context_iommu.c#L124"><tt><font size="2">http://elixir.free-electrons.com/linux/v4.13.11/source/arch/powerpc/mm/mmu_context_iommu.c#L124</font></tt></a><br><tt><font size="2">on </font></tt><tt><font size="2">VFIO_IOMMU_SPAPR_REGISTER_MEMORY.</font></tt><tt><font size="2"> From my understanding only pages</font></tt><br><tt><font size="2">that have been registered through here can be mapped with MAP_DMA.</font></tt><br><br><tt><font size="2">Cheers,</font></tt><br><tt><font size="2">Jonas<br></font></tt><BR> </body></html>
On 06/11/17 21:45, Michael Ellerman wrote: > Alexey Kardashevskiy <aik@ozlabs.ru> writes: > >> On 31/10/17 15:04, Alexey Kardashevskiy wrote: >>> DMA windows can only have a size of power of two on IODA2 hardware and >>> using memory_hotplug_max() to determine the upper limit won't work >>> correcly if it returns not power of two value. >>> >>> This relaxes the check by rounding up the value returned by >>> memory_hotplug_max(). >>> >>> It is expected to impact DPDK on machines with non-power-of-two RAM size, >>> mostly. KVM guests are less likely to be affected as usually guests get >>> less than half of hosts RAM. >> >> >> It was pointed out that this check is quite useless anyway as the vm_locked >> memory limit should hit first, and if that is not set or the user got the >> root privilege level, then there are easier ways to crash the host so I am >> thinking of: >> >> >> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c >> b/arch/powerpc/platforms/powernv/pci-ioda.c >> index 269f119e4b3c..a47e4cf343b2 100644 >> --- a/arch/powerpc/platforms/powernv/pci-ioda.c >> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c >> @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, >> __u64 bus_offset, >> if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) >> return -EINVAL; >> >> - if ((window_size > memory_hotplug_max()) || >> !is_power_of_2(window_size)) >> + if (!is_power_of_2(window_size)) >> return -EINVAL; >> >> >> >> Makes sense? > > Sounds reasonable. > > Execpt where is the vm_locked check? I think it's in the VFIO driver? Yes, as Jonas already said. > If > so I guess the only concern is that this code might be called via some > other path that doesn't do that check. It is also called from pnv_pci_ioda2_setup_default_config() to create a 32bit DMA window which is limited by __rounddown_pow_of_two(memory_hotplug_max()). I'll repost. Thanks.
diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c index 269f119e4b3c..4c62162da181 100644 --- a/arch/powerpc/platforms/powernv/pci-ioda.c +++ b/arch/powerpc/platforms/powernv/pci-ioda.c @@ -2769,7 +2769,8 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset, if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) return -EINVAL; - if ((window_size > memory_hotplug_max()) || !is_power_of_2(window_size)) + if ((window_size > roundup_pow_of_two(memory_hotplug_max())) || + !is_power_of_2(window_size)) return -EINVAL; /* Adjust direct table size from window_size and levels */
DMA windows can only have a size of power of two on IODA2 hardware and using memory_hotplug_max() to determine the upper limit won't work correcly if it returns not power of two value. This relaxes the check by rounding up the value returned by memory_hotplug_max(). It is expected to impact DPDK on machines with non-power-of-two RAM size, mostly. KVM guests are less likely to be affected as usually guests get less than half of hosts RAM. Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> --- arch/powerpc/platforms/powernv/pci-ioda.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)