Re: [RFC PATCH v2 15/25] KVM: nSVM: Call nested_svm_transition_tlb_flush() on every VMCB switch

[Yosry Ahmed <yosry@kernel.org>]

On Wed, Jul 22, 2026 at 05:42:30PM -0700, Sean Christopherson wrote:
> On Tue, Jun 16, 2026, Yosry Ahmed wrote:
> > Move the calls to nested_svm_transition_tlb_flush() in different
> > transition code paths to svm_switch_vmcb(). This ensures that TLB
> > flushes are not missed during switches, and makes it clearer that the
> > TLB flushes are directly related to the active VMCB.
> > 
> > The ordering currently doesn't matter, but as more TLB handling is added
> > for nested, requesting the TLB flushes *after* the VMCB switch will
> > become a requirement.
> > 
> > No functional change intended (for now).
> > 
> > Signed-off-by: Yosry Ahmed <yosry@kernel.org>
> > ---
> >  arch/x86/kvm/svm/nested.c | 10 ++++------
> >  1 file changed, 4 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 24a52aefe94ee..9a917d057aa8e 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -707,8 +707,12 @@ static void nested_svm_transition_tlb_flush(struct kvm_vcpu *vcpu)
> >  
> >  static void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb)
> >  {
> > +	struct kvm_vcpu *vcpu = &svm->vcpu;
> > +
> >  	svm->current_vmcb = target_vmcb;
> >  	svm->vmcb = target_vmcb->ptr;
> > +
> > +	nested_svm_transition_tlb_flush(vcpu);
> 
> I'm not convinced this is the right place to do the flushing.  Yes, manually
> doing the flushes requires more code, and arguably makes KVM less robust, but
> IMO there's value in mimicking architectural flows because it's the architecture
> that dictates the flushing.

Responded to the same comment in patch 17.