linux-kernel - [PATCH v4 10/13] KVM: x86/mmu: Bypass __handle_changed

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Date:   Tue, 21 Mar 2023 15:00:18 -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 10/13] KVM: x86/mmu: Bypass __handle_changed_spte() when
 aging TDP MMU SPTEs

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

Drop everything except the "tdp_mmu_spte_changed" tracepoint part of
__handle_changed_spte() when aging SPTEs in the TDP MMU, as clearing the
accessed status doesn't affect the SPTE's shadow-present status, whether
or not the SPTE is a leaf, or change the PFN.  I.e. none of the functional
updates handled by __handle_changed_spte() are relevant.

Losing __handle_changed_spte()'s sanity checks does mean that a bug could
theoretical go unnoticed, but that scenario is extremely unlikely, e.g.
would effectively require a misconfigured MMU or a locking bug elsewhere.

Link: https://lore.kernel.org/all/Y9HcHRBShQgjxsQb@google.com
Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
Reviewed-by: David Matlack <dmatlack@...gle.com>
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 29bb97ff266e..cdfb67ef5800 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1275,8 +1275,8 @@ static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
 							iter->level);
 	}
 
-	__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
-			      new_spte, iter->level, false);
+	trace_kvm_tdp_mmu_spte_changed(iter->as_id, iter->gfn, iter->level,
+				       iter->old_spte, new_spte);
 	return true;
 }
 
-- 
2.40.0.rc2.332.ga46443480c-goog