linux-kernel - [PATCH 06/24] kvm: x86/mmu: Skip no-op changes in TDP MMU functions

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Date:   Tue, 12 Jan 2021 10:10:23 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 06/24] kvm: x86/mmu: Skip no-op changes in TDP MMU functions

Skip setting SPTEs if no change is expected.

Reviewed-by: Peter Feiner <pfeiner@...gle.com>

Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 1987da0da66e..2650fa9fe066 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -882,6 +882,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		    !is_last_spte(iter.old_spte, iter.level))
 			continue;
 
+		if (!(iter.old_spte & PT_WRITABLE_MASK))
+			continue;
+
 		new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
 
 		tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);
@@ -1079,6 +1082,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		if (!is_shadow_present_pte(iter.old_spte))
 			continue;
 
+		if (iter.old_spte & shadow_dirty_mask)
+			continue;
+
 		new_spte = iter.old_spte | shadow_dirty_mask;
 
 		tdp_mmu_set_spte(kvm, &iter, new_spte);
-- 
2.30.0.284.gd98b1dd5eaa7-goog