Re: [PATCH v2] iommu/vt-d: Add a fix for devices need extra dtlb flush

[Baolu Lu]

Hi Jacob,

On 2022/11/29 1:04, Jacob Pan wrote:
> QAT devices on Intel Sapphire Rapids and Emerald Rapids have a defect in
> address translation service (ATS). These devices may inadvertently issue
> ATS invalidation completion before posted writes initiated with
> translated address that utilized translations matching the invalidation
> address range, violating the invalidation completion ordering.
>
> This patch adds an extra device TLB invalidation for the affected devices,
> it is needed to ensure no more posted writes with translated address
> following the invalidation completion. Therefore, the ordering is
> preserved and data-corruption is prevented.
>
> Device TLBs are invalidated under the following six conditions:
> 1. Device driver does DMA API unmap IOVA
> 2. Device driver unbind a PASID from a process, sva_unbind_device()
> 3. PASID is torn down, after PASID cache is flushed. e.g. process
> exit_mmap() due to crash
> 4. Under SVA usage, called by mmu_notifier.invalidate_range() where
> VM has to free pages that were unmapped
> 5. userspace driver unmaps a DMA buffer
> 6. Cache invalidation in vSVA usage (upcoming)
>
> For #1 and #2, device drivers are responsible for stopping DMA traffic
> before unmap/unbind. For #3, iommu driver gets mmu_notifier to
> invalidate TLB the same way as normal user unmap which will do an extra
> invalidation. The dTLB invalidation after PASID cache flush does not
> need an extra invalidation.
>
> Therefore, we only need to deal with #4 and #5 in this patch. #1 is also
> covered by this patch due to common code path with #5.
>
> Tested-by: Yuzhang Luo <yuzhang.luo@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Reviewed-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> ---
> v2
> - removed risky_device() check based on the review by Robin, added comments
>    to explain the exemption.
> - reworked commit message based on the review from Ashok
> ---
>   drivers/iommu/intel/iommu.c | 67 +++++++++++++++++++++++++++++++++++--
>   drivers/iommu/intel/iommu.h |  3 ++
>   drivers/iommu/intel/svm.c   |  4 ++-
>   3 files changed, 71 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 996a8b5ee5ee..a97e9247037f 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1396,6 +1396,23 @@ static void domain_update_iotlb(struct dmar_domain *domain)
>   	spin_unlock_irqrestore(&domain->lock, flags);
>   }
>   
> +/*
> + * Impacted QAT device IDs ranging from 0x4940 to 0x4943.
> + * This quirk is exempted from risky_device() check because it applies only
> + * to the built-in QAT devices.
> + */

How about adding:

"This quirk is exempted from risky_device() check because it doesn't
effectively grant additional privileges."

?

--
Best regards,
baolu