Re: [PATCH v2 09/10] iommu/vt-d: Follow PT_FEAT_DMA_INCOHERENT into the PASID entry

[Baolu Lu <baolu.lu@linux.intel.com>]

On 8/27/2025 1:26 AM, Jason Gunthorpe wrote:
> Currently a incoherent walk domain cannot be attached do a coherent
> capable iommu. Kevin says HW probably doesn't exist with such a mixture,
> but make the driver make logical sense anyhow.
> 
> When building the PASID entry the PWSNP (Page Walk Snoop) bit tells the HW
> if it should issue snoops. If the page table is cache flushed because of
> PT_FEAT_DMA_INCOHERENT then it is fine to set this bit to 0 even if the HW
> supports 1.
> 
> Weaken the compatible check to permit a coherent instance to accept an
> incoherent table and fix the PASID table construction to set PWSNP from
> PT_FEAT_DMA_INCOHERENT.
> 
> SVA always sets PWSNP.
> 
> Signed-off-by: Jason Gunthorpe<jgg@nvidia.com>
> ---
>   drivers/iommu/intel/iommu.c |  8 ++++++--
>   drivers/iommu/intel/pasid.c | 31 ++++++++++++++-----------------
>   drivers/iommu/intel/pasid.h |  1 +
>   drivers/iommu/intel/svm.c   |  1 +
>   4 files changed, 22 insertions(+), 19 deletions(-)

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>