linux-kernel - [PATCH v4 09/13] KVM: x86/mmu: Drop unnecessary dirty log checks when aging TDP MMU SPTEs

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Message-ID: <20230321220021.2119033-10-seanjc@google.com>
Date:   Tue, 21 Mar 2023 15:00:17 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v4 09/13] KVM: x86/mmu: Drop unnecessary dirty log checks when
 aging TDP MMU SPTEs

From: Vipin Sharma <vipinsh@...gle.com>

Drop the unnecessary call to handle dirty log updates when aging TDP MMU
SPTEs, as neither clearing the Accessed bit nor marking a SPTE for access
tracking can _set_ the Writable bit, i.e. can't trigger marking a gfn
dirty in its memslot.  The access tracking path can _clear_ the Writable
bit, e.g. if the XCHG races with fast_page_fault() and writes the stale
value without the Writable bit set, but clearing the Writable bit outside
of mmu_lock is not allowed, i.e. access tracking can't spuriously set the
Writable bit.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
[sean: split to separate patch, apply to dirty path, write changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index adbdfed287cc..29bb97ff266e 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1277,8 +1277,6 @@ static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
 
 	__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
 			      new_spte, iter->level, false);
-	handle_changed_spte_dirty_log(kvm, iter->as_id, iter->gfn,
-				      iter->old_spte, new_spte, iter->level);
 	return true;
 }
 
-- 
2.40.0.rc2.332.ga46443480c-goog