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

[Zhang, Tina]

> -----Original Message-----
> From: iommu <iommu-bounces@xxxxxxxxxxxxxxxxxxxxxxxxxx> On Behalf Of
> David Stevens
> Sent: Wednesday, March 16, 2022 1:07 PM
> To: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David
> Stevens <stevensd@xxxxxxxxxxxx>
> Subject: [PATCH] iommu/vt-d: check alignment before using psi
> 
> 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 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.

Indeed, the dma_map/unmap always use alloca_iova(..., true) to allocate iova, which means size_aligned. But the iova used by userspace might not be size aligned. And it seems we cannot expect userspace can always use size_aligned iova base address.

BR,
Tina

> 
> 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
> 
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