Re: [PATCH 1/1] Revert "iommu/vt-d: Clean up pasid quirk for pre-production devices"

[Zhenyu Wang]

On 2018.07.16 14:02:12 +0800, Lu Baolu wrote:
> Hi Joerg,
> 
> The graphic guys are looking forward to having this in 4.18.
> Is it possible to take it in the following rcs?
> 

This breakes intel gfx driver in 4.18 when gfx dmar is on.
Please include this fix ASAP.

Tested-by: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>

thanks!

> 
> On 07/08/2018 02:23 PM, Lu Baolu wrote:
> > This reverts commit ab96746aaa344fb720a198245a837e266fad3b62.
> >
> > The commit ab96746aaa34 ("iommu/vt-d: Clean up pasid quirk for
> > pre-production devices") triggers ECS mode on some platforms
> > which have broken ECS support. As the result, graphic device
> > will be inoperable on boot.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107017
> >
> > Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/intel-iommu.c | 32 ++++++++++++++++++++++++++++++--
> >  include/linux/intel-iommu.h |  1 +
> >  2 files changed, 31 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index b344a88..115ff26 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -484,14 +484,37 @@ static int dmar_forcedac;
> >  static int intel_iommu_strict;
> >  static int intel_iommu_superpage = 1;
> >  static int intel_iommu_ecs = 1;
> > +static int intel_iommu_pasid28;
> >  static int iommu_identity_mapping;
> >  
> >  #define IDENTMAP_ALL		1
> >  #define IDENTMAP_GFX		2
> >  #define IDENTMAP_AZALIA		4
> >  
> > -#define ecs_enabled(iommu)	(intel_iommu_ecs && ecap_ecs(iommu->ecap))
> > -#define pasid_enabled(iommu)	(ecs_enabled(iommu) && ecap_pasid(iommu->ecap))
> > +/* Broadwell and Skylake have broken ECS support â normal so-called "second
> > + * level" translation of DMA requests-without-PASID doesn't actually happen
> > + * unless you also set the NESTE bit in an extended context-entry. Which of
> > + * course means that SVM doesn't work because it's trying to do nested
> > + * translation of the physical addresses it finds in the process page tables,
> > + * through the IOVA->phys mapping found in the "second level" page tables.
> > + *
> > + * The VT-d specification was retroactively changed to change the definition
> > + * of the capability bits and pretend that Broadwell/Skylake never happened...
> > + * but unfortunately the wrong bit was changed. It's ECS which is broken, but
> > + * for some reason it was the PASID capability bit which was redefined (from
> > + * bit 28 on BDW/SKL to bit 40 in future).
> > + *
> > + * So our test for ECS needs to eschew those implementations which set the old
> > + * PASID capabiity bit 28, since those are the ones on which ECS is broken.
> > + * Unless we are working around the 'pasid28' limitations, that is, by putting
> > + * the device into passthrough mode for normal DMA and thus masking the bug.
> > + */
> > +#define ecs_enabled(iommu) (intel_iommu_ecs && ecap_ecs(iommu->ecap) && \
> > +			    (intel_iommu_pasid28 || !ecap_broken_pasid(iommu->ecap)))
> > +/* PASID support is thus enabled if ECS is enabled and *either* of the old
> > + * or new capability bits are set. */
> > +#define pasid_enabled(iommu) (ecs_enabled(iommu) &&			\
> > +			      (ecap_pasid(iommu->ecap) || ecap_broken_pasid(iommu->ecap)))
> >  
> >  int intel_iommu_gfx_mapped;
> >  EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped);
> > @@ -554,6 +577,11 @@ static int __init intel_iommu_setup(char *str)
> >  			printk(KERN_INFO
> >  				"Intel-IOMMU: disable extended context table support\n");
> >  			intel_iommu_ecs = 0;
> > +		} else if (!strncmp(str, "pasid28", 7)) {
> > +			printk(KERN_INFO
> > +				"Intel-IOMMU: enable pre-production PASID support\n");
> > +			intel_iommu_pasid28 = 1;
> > +			iommu_identity_mapping |= IDENTMAP_GFX;
> >  		} else if (!strncmp(str, "tboot_noforce", 13)) {
> >  			printk(KERN_INFO
> >  				"Intel-IOMMU: not forcing on after tboot. This could expose security risk for tboot\n");
> > diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> > index 1df9401..ef169d6 100644
> > --- a/include/linux/intel-iommu.h
> > +++ b/include/linux/intel-iommu.h
> > @@ -121,6 +121,7 @@
> >  #define ecap_srs(e)		((e >> 31) & 0x1)
> >  #define ecap_ers(e)		((e >> 30) & 0x1)
> >  #define ecap_prs(e)		((e >> 29) & 0x1)
> > +#define ecap_broken_pasid(e)	((e >> 28) & 0x1)
> >  #define ecap_dis(e)		((e >> 27) & 0x1)
> >  #define ecap_nest(e)		((e >> 26) & 0x1)
> >  #define ecap_mts(e)		((e >> 25) & 0x1)
> 

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