Re: IOMMU regression in linux-6.18.y

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jan 21, 2026 at 03:32:42PM +0800, Baolu Lu wrote:
> 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.

Ok, all now queued up, thanks.

greg k-h