[Intel-gfx] [PATCH 1/4] iommu/vt-d: Disable superpage for Geminilake igfx

[Ville Syrjälä]

On Mon, Jul 12, 2021 at 07:23:07AM +0800, Lu Baolu wrote:
> On 7/10/21 12:47 AM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > While running "gem_exec_big --r single" from igt-gpu-tools on
> > Geminilake as soon as a 2M mapping is made I tend to get a DMAR
> > write fault. Strangely the faulting address is always a 4K page
> > and usually very far away from the 2M page that got mapped.
> > But if no 2M mappings get used I can't reproduce the fault.
> > 
> > I also tried to dump the PTE for the faulting address but it actually
> > looks correct to me (ie. definitely seems to have the write bit set):
> >   DMAR: DRHD: handling fault status reg 2
> >   DMAR: [DMA Write] Request device [00:02.0] PASID ffffffff fault addr 7fa8a78000 [fault reason 05] PTE Write access is not set
> >   DMAR: fault 7fa8a78000 (level=1) PTE = 149efc003
> > 
> > So not really sure what's going on and this might just be full on duct
> > tape, but it seems to work here. The machine has now survived a whole day
> > running that test whereas with superpage enabled it fails in less than
> > a minute usually.
> > 
> > TODO: might be nice to disable superpage only for the igfx iommu
> >        instead of both iommus
> 
> If all these quirks are about igfx dedicated iommu's, I would suggest to
> disable superpage only for the igfx ones.

Sure. Unfortunately there's no convenient mechanism to do that in
the iommu driver that I can immediately see. So not something I
can just whip up easily. Since you're actually familiar with the
driver maybe you can come up with a decent solution for that?

> 
> Best regards,
> baolu
> 
> > TODO: would be nice to use the macros from include/drm/i915_pciids.h,
> >        but can't do that with DECLARE_PCI_FIXUP_HEADER()
> > 
> > Cc: David Woodhouse <dwmw2 at infradead.org>
> > Cc: Lu Baolu <baolu.lu at linux.intel.com>
> > Cc: iommu at lists.linux-foundation.org
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > ---
> >   drivers/iommu/intel/iommu.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 19c7888cbb86..4fff2c9c86af 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -5617,6 +5617,16 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x1632, quirk_iommu_igfx);
> >   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163A, quirk_iommu_igfx);
> >   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163D, quirk_iommu_igfx);
> >   
> > +static void quirk_iommu_nosp(struct pci_dev *dev)
> > +{
> > +	pci_info(dev, "Disabling IOMMU superpage for graphics on this chipset\n");
> > +	intel_iommu_superpage = 0;
> > +}
> > +
> > +/* Geminilake igfx appears to have issues with superpage */
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x3184, quirk_iommu_nosp);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x3185, quirk_iommu_nosp);
> > +
> >   static void quirk_iommu_rwbf(struct pci_dev *dev)
> >   {
> >   	if (risky_device(dev))
> > 

-- 
Ville Syrjälä
Intel