Re: [PATCH] commit 6b080c4e815ceba3c08ffa980c858595c07e786a upstream

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Oct 01, 2025 at 09:19:09PM +0000, Zhichuang Sun wrote:
> iommu/amd: fix amd iotlb flush range in unmap

Shouldn't this be the subject line?

> This was fixed in mainline in 6b080c4e815ceba3c08ffa980c858595c07e786a,
> but do not backport the full refactor.

Why not?

> Targeting branch lts linux-5.15.y.

Why just this one?  Why not also 5.10.y and 5.4.y?

> AMD IOMMU driver supports power of 2 KB page size, it can be 4K, 8K,
> 16K, etc. So when VFIO driver ask AMD IOMMU driver to unmap a
> IOVA with a page_size 4K, it actually can unmap a page_size of
> 8K, depending on the page used during mapping. However, the iotlb
> gather function use the page_size as the range of unmap range,
> instead of the real unmapped page size r.
> 
> This miscalculation of iotlb flush range will make the unflushed
> IOTLB entry stale. It triggered hard-to-debug silent data corruption
> issue as DMA engine who used the stale IOTLB entry will DMA into
> unmapped memory region.
> 
> The upstream commit aims at changing API from map/unmap_page() to
> map/unmap_pages() and changed the gather range calculation along
> with it. It accidentally fixed this bug in the mainline since 6.1.
> For this backport, we don't backport the API change, only port the
> gather range calculation to fix the bug.
> 
> Cc: Nadav Amit <namit@vmware.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Cc: iommu@lists.linux-foundation.org
> Fixes: fc65d0acaf23179b94de399c204328fa259acb90

Please use the proper format as documented:

Fixes: fc65d0acaf23 ("iommu/amd: Selective flush on unmap")

thanks,

greg k-h