Re: [PATCH 1/3] KVM: x86: Mark TSS busy during LTR emulation _after_ all fault checks

[Sean Christopherson]

On Tue, Jul 12, 2022, Maxim Levitsky wrote:
> On Mon, 2022-07-11 at 23:27 +0000, Sean Christopherson wrote:
> > Wait to mark the TSS as busy during LTR emulation until after all fault
> > checks for the LTR have passed.  Specifically, don't mark the TSS busy if
> > the new TSS base is non-canonical.
> 
> 
> Took me a while to notice it but I see the canonical check now, so the patch
> makes sense, and so:
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> 
> Unrelated, but I do wonder why we use cmpxchg_emulated for setting the busy
> bit, while we use write_segment_descriptor to set the accessed bit.

99% certain it's a historical KVM bug in how it updates the accessed bit.