Re: [RFC PATCH v5 02/45] KVM: x86/mmu: Update iter->old_spte if cmpxchg64 on mirror SPTE "fails"

[Huang, Kai]

On Tue, 2026-02-03 at 12:06 -0800, Sean Christopherson wrote:
> On Tue, Feb 03, 2026, Kai Huang wrote:
> > On Wed, 2026-01-28 at 17:14 -0800, Sean Christopherson wrote:
> > > Pass a pointer to iter->old_spte, not simply its value, when setting an
> > > external SPTE in __tdp_mmu_set_spte_atomic(), so that the iterator's value
> > > will be updated if the cmpxchg64 to freeze the mirror SPTE fails.  The bug
> > > is currently benign as TDX is mutualy exclusive with all paths that do
> > > "local" retry", e.g. clear_dirty_gfn_range() and wrprot_gfn_range().
> > > 
> > > Fixes: 77ac7079e66d ("KVM: x86/tdp_mmu: Propagate building mirror page tables")
> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > 
> > Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
> > 
> > Btw, do we need to cc stable?
> 
> Probably not?  The bug is benign until dirty logging comes along, and if someone
> backports that support (if it ever manifests) to an older kernel, it's firmly
> that person's responsibility to pick up dependencies like this.

Makes sense. :-)