iommu/vt-d: Treat PAGE_SNOOP and PWSNP separately

[PATCH] iommu/vt-d: Treat PAGE_SNOOP and PWSNP separately

Posted by Viktor Kleen 4 days, 8 hours ago

The PASID_FLAG_PAGE_SNOOP and PASID_FLAG_PWSNP constants are identical.
This will cause the pasid code to always set both or neither of the
PGSNP and PWSNP bits in PASID table entries. However, PWSNP is a
reserved bit if SMPWC is not set in the IOMMU's extended capability
register, even if SC is supported.

This has resulted in DMAR errors when testing the iommufd code on an
Arrow Lake platform. With this patch, those errors disappear and the
PASID table entries look correct.

Fixes: 101a2854110fa ("iommu/vt-d: Follow PT_FEAT_DMA_INCOHERENT into the PASID entry")
Signed-off-by: Viktor Kleen <viktor@kleen.org>
---
 drivers/iommu/intel/pasid.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/pasid.h b/drivers/iommu/intel/pasid.h
index b4c85242dc79..3809793e0259 100644
--- a/drivers/iommu/intel/pasid.h
+++ b/drivers/iommu/intel/pasid.h
@@ -24,7 +24,7 @@
 
 #define PASID_FLAG_NESTED		BIT(1)
 #define PASID_FLAG_PAGE_SNOOP		BIT(2)
-#define PASID_FLAG_PWSNP		BIT(2)
+#define PASID_FLAG_PWSNP		BIT(3)
 
 /*
  * The PASID_FLAG_FL5LP flag Indicates using 5-level paging for first-
-- 
2.51.0

Re: [PATCH] iommu/vt-d: Treat PAGE_SNOOP and PWSNP separately

Posted by Baolu Lu 1 day, 18 hours ago

On 2/3/26 03:21, Viktor Kleen wrote:
> The PASID_FLAG_PAGE_SNOOP and PASID_FLAG_PWSNP constants are identical.
> This will cause the pasid code to always set both or neither of the
> PGSNP and PWSNP bits in PASID table entries. However, PWSNP is a
> reserved bit if SMPWC is not set in the IOMMU's extended capability
> register, even if SC is supported.
> 
> This has resulted in DMAR errors when testing the iommufd code on an
> Arrow Lake platform. With this patch, those errors disappear and the
> PASID table entries look correct.
> 
> Fixes: 101a2854110fa ("iommu/vt-d: Follow PT_FEAT_DMA_INCOHERENT into the PASID entry")
> Signed-off-by: Viktor Kleen<viktor@kleen.org>
> ---
>   drivers/iommu/intel/pasid.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Queued for iommu/vt-d.

Thanks,
baolu

Re: [PATCH] iommu/vt-d: Treat PAGE_SNOOP and PWSNP separately

Posted by Jason Gunthorpe 4 days, 3 hours ago

On Mon, Feb 02, 2026 at 07:21:05PM +0000, Viktor Kleen wrote:
> The PASID_FLAG_PAGE_SNOOP and PASID_FLAG_PWSNP constants are identical.
> This will cause the pasid code to always set both or neither of the
> PGSNP and PWSNP bits in PASID table entries. However, PWSNP is a
> reserved bit if SMPWC is not set in the IOMMU's extended capability
> register, even if SC is supported.
> 
> This has resulted in DMAR errors when testing the iommufd code on an
> Arrow Lake platform. With this patch, those errors disappear and the
> PASID table entries look correct.
> 
> Fixes: 101a2854110fa ("iommu/vt-d: Follow PT_FEAT_DMA_INCOHERENT into the PASID entry")
> Signed-off-by: Viktor Kleen <viktor@kleen.org>
> ---
>  drivers/iommu/intel/pasid.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

It looks like a typo to me too

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

It should also be:

Cc: stable@vger.kernel.org

Jason