Messages in this thread | | | From | "Maciej S. Szmigiero" <> | Subject | Re: [PATCH 2/3] KVM: x86/mmu: Drop a redundant remote TLB flush in kvm_zap_gfn_range() | Date | Fri, 22 Oct 2021 13:44:44 +0200 |
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On 22.10.2021 03:00, Sean Christopherson wrote: > Remove an unnecessary remote TLB flush in kvm_zap_gfn_range() now that > said function holds mmu_lock for write for its entire duration. The > flush was added by the now-reverted commit to allow TDP MMU to flush while > holding mmu_lock for read, as the transition from write=>read required > dropping the lock and thus a pending flush needed to be serviced. > > Fixes: 5a324c24b638 ("Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock"") > Cc: Maxim Levitsky <mlevitsk@redhat.com> > Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> > Cc: Ben Gardon <bgardon@google.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/mmu/mmu.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index f82b192bba0b..e8b8a665e2e9 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -5700,9 +5700,6 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end) > end - 1, true, flush); > } > } > - if (flush) > - kvm_flush_remote_tlbs_with_address(kvm, gfn_start, > - gfn_end - gfn_start); > } > > if (is_tdp_mmu_enabled(kvm)) { >
Unfortunately, it seems that a pending flush from __kvm_zap_rmaps() can be reset back to false by the following line: > flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start, gfn_end, flush);
kvm_tdp_mmu_zap_gfn_range() calls __kvm_tdp_mmu_zap_gfn_range with "can_yield" set to true, which passes it to zap_gfn_range, which has this code: > if (can_yield && > tdp_mmu_iter_cond_resched(kvm, &iter, flush, shared)) { > flush = false; > continue; > }
Thanks, Maciej
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