On Tue, Apr 06, 2021, Paolo Bonzini wrote:

Right now, if a call to kvm_tdp_mmu_zap_sp returns false, the caller will skip the TLB flush, which is wrong. There are two ways to fix it:

• since kvm_tdp_mmu_zap_sp will not yield and therefore will not flush the TLB itself, we could change the call to kvm_tdp_mmu_zap_sp to use "flush |= ..."

• or we can chain the flush argument through kvm_tdp_mmu_zap_sp down to __kvm_tdp_mmu_zap_gfn_range.

This patch does the former to simplify application to stable kernels.

Eh, that and passing flush down the stack is pointless because kvm_tdp_mmu_zap_sp() will never yield. If you want to justify |= over passing flush, it probably makes sense to link to the discussion that led to me changing from passing flush to accumulating the result (well, tried to, doh).

https://lkml.kernel.org/r/20210319232006.3468382-3-seanjc@google.com

Cc: seanjc@google.com Fixes: 048f49809c526 ("KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping") Cc: stable@vger.kernel.org # 5.10.x: 048f49809c: KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping Cc: stable@vger.kernel.org # 5.10.x: 33a3164161: KVM: x86/mmu: Don't allow TDP MMU to yield when recovering NX pages Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com

Reviewed-by: Sean Christopherson seanjc@google.com

---

arch/x86/kvm/mmu/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 486aa94ecf1d..951dae4e7175 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5906,7 +5906,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) lpage_disallowed_link); WARN_ON_ONCE(!sp->lpage_disallowed); if (is_tdp_mmu_page(sp)) {

• 	flush = kvm_tdp_mmu_zap_sp(kvm, sp);
  

• 	flush |= kvm_tdp_mmu_zap_sp(kvm, sp);
  

  } else { kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list); WARN_ON_ONCE(sp->lpage_disallowed);

-- 2.26.2