RE: [PATCH] iommu/vt-d: check alignment before using psi

[Tian, Kevin]

> From: David Stevens <stevensd@xxxxxxxxxxxx>
> Sent: Wednesday, March 16, 2022 1:07 PM
> 
> From: David Stevens <stevensd@xxxxxxxxxxxx>
> 
> Fall back to domain selective flush if the target address is not aligned
> to the mask being used for invalidation. This is necessary because page

using domain selective flush is a bit conservative. What about trying
mask+1 first?

> selective invalidation masks out the lower order bits of the target
> address based on the mask value, so if a non-aligned address is targeted
> for psi, then mappings at the end of [pfn, pfn+pages) may not properly
> be flushed from the iotlb.
> 
> This is not normally an issue because iova.c always allocates iovas that
> are aligned to their size. However, iovas which come from other sources
> (e.g. userspace via VFIO) may not be aligned.
> 
> Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/iommu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 5b196cfe9ed2..c122686e0a5c 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1735,7 +1735,8 @@ static void iommu_flush_iotlb_psi(struct
> intel_iommu *iommu,
>  		 * and the base address is naturally aligned to the size.
>  		 */
>  		if (!cap_pgsel_inv(iommu->cap) ||
> -		    mask > cap_max_amask_val(iommu->cap))
> +		    mask > cap_max_amask_val(iommu->cap) ||
> +		    unlikely(((1 << mask) - 1) & pfn))
>  			iommu->flush.flush_iotlb(iommu, did, 0, 0,
> 
> 	DMA_TLB_DSI_FLUSH);
>  		else
> --
> 2.35.1.723.g4982287a31-goog