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

[Edgecombe, Rick P]

On Thu, 2026-01-29 at 14:23 -0800, Sean Christopherson wrote:
> No, the bug is if the cmpxchg64 fails.  On failure, the current mismatching value
> is stored in the "old" param.  KVM relies on the iter->old_spte holding the
> current value when restarting an operation without re-reading the SPTE from memory.

Ah, I see. Sorry. Just went and refreshed up on the difference between
cmpxchg64() and try_cmpxchg64(). I see now that the log is accurate since it
refers to the behavior of the instruction, but specifying try_cmpxchg64() might
be a little clearer since cmpxchg() doesn't automatically update the 'old'
passed in. In either case:

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>