Re: IOMMU regression in linux-6.18.y

[Baolu Lu <baolu.lu@linux.intel.com>]

On 1/21/26 15:26, Greg KH wrote:
> On Wed, Jan 21, 2026 at 03:14:42PM +0800, Baolu Lu wrote:
>> 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.
> 
> So all should be backported?  If so, great, but why were they not tagged
> as such?

Yes, they should be backported. I am sorry; we should have tagged them
at the time we upstreamed them.

> 
> thanks,
> 
> greg k-h
> 

Thanks,
baolu