diff options
| author | Sean Christopherson <seanjc@google.com> | 2022-02-26 03:15:23 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-03-08 17:31:36 +0300 |
| commit | 7ae5840e6f3325b52ee46437d46ba0465016584d (patch) | |
| tree | 46cf6d49f9fbfde1fba9d64c6fbacf1661cc4fd4 /arch/x86/kvm/mmu/tdp_mmu.c | |
| parent | db01416b22d98b8c8474a418a97cdacfd947469d (diff) | |
| download | linux-7ae5840e6f3325b52ee46437d46ba0465016584d.tar.xz | |
KVM: x86/mmu: Document that zapping invalidated roots doesn't need to flush
Remove the misleading flush "handling" when zapping invalidated TDP MMU
roots, and document that flushing is unnecessary for all flavors of MMUs
when zapping invalid/obsolete roots/pages. The "handling" in the TDP MMU
is dead code, as zap_gfn_range() is called with shared=true, in which
case it will never return true due to the flushing being handled by
tdp_mmu_zap_spte_atomic().
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/mmu/tdp_mmu.c')
| -rw-r--r-- | arch/x86/kvm/mmu/tdp_mmu.c | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 921fa386df99..2ce6915b70fe 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -851,7 +851,6 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) { struct kvm_mmu_page *next_root; struct kvm_mmu_page *root; - bool flush = false; lockdep_assert_held_read(&kvm->mmu_lock); @@ -864,7 +863,16 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) rcu_read_unlock(); - flush = zap_gfn_range(kvm, root, 0, -1ull, true, flush, true); + /* + * A TLB flush is unnecessary, invalidated roots are guaranteed + * to be unreachable by the guest (see kvm_tdp_mmu_put_root() + * for more details), and unlike the legacy MMU, no vCPU kick + * is needed to play nice with lockless shadow walks as the TDP + * MMU protects its paging structures via RCU. Note, zapping + * will still flush on yield, but that's a minor performance + * blip and not a functional issue. + */ + (void)zap_gfn_range(kvm, root, 0, -1ull, true, false, true); /* * Put the reference acquired in @@ -878,9 +886,6 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) } rcu_read_unlock(); - - if (flush) - kvm_flush_remote_tlbs(kvm); } /* |