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@xxxxxxxxxx > Cc: seanjc@xxxxxxxxxx > Fixes: 048f49809c526 ("KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping") > Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x: 048f49809c: KVM: x86/mmu: Ensure TLBs are flushed for TDP MMU during NX zapping > Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x: 33a3164161: KVM: x86/mmu: Don't allow TDP MMU to yield when recovering NX pages > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > 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 >
