Re: [PATCH 2/2] KVM: Don't take mmu_lock for range invalidation unless necessary
From: Sean Christopherson <seanjc@google.com>
Date: 2021-08-02 19:05:23
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lkml
On Tue, Jul 27, 2021, Paolo Bonzini wrote:
quoted hunk ↗ jump to hunk
@@ -605,8 +597,13 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, /* * .change_pte() must be surrounded by .invalidate_range_{start,end}(), + * If mmu_notifier_count is zero, then start() didn't find a relevant + * memslot and wasn't forced down the slow path; rechecking here is + * unnecessary.
Critiquing my own comment... Maybe elaborate on what's (not) being rechecked? And also clarify that rechecking the memslots on a false positive (due to a second invalidation) is not problematic? * If mmu_notifier_count is zero, then no in-progress invalidations, * including this one, found a relevant memslot at start(); rechecking * memslots here is unnecessary. Note, a false positive (count elevated * by a different invalidation) is sub-optimal but functionally ok. */ Thanks for doing the heavy lifting!
*/ WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count)); + if (!kvm->mmu_notifier_count) + return; kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); }