Re: [PATCH v3 2/5] iommu/amd: Fix DTE clearing and rename iommu_ignore_device()

[Samiullah Khawaja]

On Mon, Aug 24, 2026 at 12:23:44PM +0000, Pranjal Shrivastava wrote:
> The iommu_ignore_device() function currently uses memset() to manually
> clear the primary Device Table Entry (DTE), which risks torn writes as
> the hardware reads DTEs as atomic 256-bit qwords. Furthermore, clearing
> the primary devid in the lookup table before calling setup_aliases()
> causes rlookup_amd_iommu() to fail for aliases. This prevents clearing
> the DTEs for DMA aliases.
>
> Fix this by replacing the manual memset with a dedicated helper that
> invalidates the DTE by clearing the lower 128 bits (having the Valid bit)
> first, followed by the upper 128 bits. The cleared state is then
> explicitly cloned to all aliases before the lookup tables are nullified.
>
> Rename the function to iommu_disable_device() more accurately
> reflects its intent, as we still support IRQ remapping for these devices)
>
> Fixes: 99fc4ac3d297 ("iommu/amd: Introduce per PCI segment alias_table")
> Reported-by: sashiko-bot@xxxxxxxxxx
> Closes: https://lore.kernel.org/all/20260529153216.2AD1E1F00899@xxxxxxxxxxxxxxx/
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Pranjal Shrivastava <praan@xxxxxxxxxx>
> ---
> drivers/iommu/amd/iommu.c | 53 ++++++++++++++++++++++++++-------------
> 1 file changed, 36 insertions(+), 17 deletions(-)

Reviewed-by: Samiullah Khawaja <skhawaja@xxxxxxxxxx>