Re: IOMMU regression in linux-6.18.y

Baolu Lu
2026-01-21T07:14:51Z

On 1/21/26 13:26, Mario Limonciello wrote:
>
>
> On 1/20/26 8:08 PM, Mario Limonciello wrote:
>> Hi,
>>
>> Recently I found out that amdxdna stopped working in linux-6.18.4.
>> This is because of this commit in linux-6.18.y:
>>
>> commit c341dee80b5d ("iommu: disable SVA when CONFIG_X86 is set")
>>
>> That was originally backported from upstream:
>>
>> commit 72f98ef9a4be ("iommu: disable SVA when CONFIG_X86 is set")
>>
>> ---
>>
>> SVA support is a requirement for amdxdna.
>>
>> The series that this commit came from was part of a larger 8 patch
>> series, but this was the only commit that was CC'ed to stable.
>>
>> As a result this is not broken in 6.19-rc, but it is broken in
>> linux-6.18.y (and presumably any older stable kernels still around
>> that picked it up).
>>
>> So there are two options I see:
>>
>> 1) Revert c341dee80b5d in linux-6.18.y (and any other stable kernel
>> that picked it up but has amdxdna)
>>
>> 2) Bring the entire 8 patch series to linux-6.18.y.
>>
>> This is the entire series (I didn't look up the hashes from mainline,
>> but they should have all landed):
>> https://lore.kernel.org/linux-iommu/20251022082635.2462433-1-
>> baolu.lu@linux.intel.com/
>>
>> What should we do?
>>
>
> If the decision is to take the remaining commits to 6.18.y to fix this I
> did confirm they cleanly cherry pick and build.  Here are the hashes.
>
> commit 27bfafac65d8 ("mm: add a ptdesc flag to mark kernel page tables")
> commit 977870522af3 ("mm: actually mark kernel page table pages")
> commit 412d000346ea ("x86/mm: use 'ptdesc' when freeing PMD pages")
> commit 018942956723 ("mm: introduce pure page table freeing function")
> commit bf9e4e30f353 ("x86/mm: use pagetable_free()")
> commit 5ba2f0a15564 ("mm: introduce deferred freeing for kernel page
> tables")
> commit e37d5a2d60a3 ("iommu/sva: invalidate stale IOTLB entries for
> kernel address space")
>

Yes. These patches fix a security issue in iommu/sva on x86 and restore
the SVA functionality.

Thanks,
baolu