linux-kernel - [Patch] KVM: x86/mmu: Make optimized __handle_changed

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Date:   Wed, 25 Jan 2023 13:38:57 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        dmatlack@...gle.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>
Subject: [Patch] KVM: x86/mmu: Make optimized __handle_changed_spte() for
 clear dirty log

Use a tone down version of __handle_changed_spte() when clearing dirty
log. Remove checks which will not be needed when dirty logs are cleared.

This change shows ~13% improvement in clear dirty log calls in
dirty_log_perf_test

Before tone down version:
Clear dirty log over 3 iterations took 10.006764203s. (Avg 3.335588067s/iteration)

After tone down version:
Clear dirty log over 3 iterations took 8.686433554s. (Avg 2.895477851s/iteration)

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index bba33aea0fb0..ca21b33c4386 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -504,6 +504,19 @@ static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
 	call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
 }
 
+static void handle_changed_spte_clear_dirty_log(int as_id, gfn_t gfn,
+						u64 old_spte, u64 new_spte,
+						int level)
+{
+	if (old_spte == new_spte)
+		return;
+
+	trace_kvm_tdp_mmu_spte_changed(as_id, gfn, level, old_spte, new_spte);
+
+	if (is_dirty_spte(old_spte) &&  !is_dirty_spte(new_spte))
+		kvm_set_pfn_dirty(spte_to_pfn(old_spte));
+}
+
 /**
  * __handle_changed_spte - handle bookkeeping associated with an SPTE change
  * @kvm: kvm instance
@@ -736,7 +749,12 @@ static u64 __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,
 
 	old_spte = kvm_tdp_mmu_write_spte(sptep, old_spte, new_spte, level);
 
-	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);
+	if (record_dirty_log)
+		__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte,
+				      level, false);
+	else
+		handle_changed_spte_clear_dirty_log(as_id, gfn, old_spte,
+						    new_spte, level);
 
 	if (record_acc_track)
 		handle_changed_spte_acc_track(old_spte, new_spte, level);
-- 
2.39.1.456.gfc5497dd1b-goog