linux-kernel - [PATCH v2 15/28] KVM: x86/mmu: Skip no-op changes in TDP MMU functions

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Date:   Tue,  2 Feb 2021 10:57:21 -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 v2 15/28] 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>

---

v1 -> v2
- Merged no-op checks into exiting old_spte check

 arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index c8a1149cb229..aeb05f626b55 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -888,7 +888,8 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 			continue;
 
 		if (!is_shadow_present_pte(iter.old_spte) ||
-		    !is_last_spte(iter.old_spte, iter.level))
+		    !is_last_spte(iter.old_spte, iter.level) ||
+		    !(iter.old_spte & PT_WRITABLE_MASK))
 			continue;
 
 		new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
@@ -1065,7 +1066,8 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
 			continue;
 
-		if (!is_shadow_present_pte(iter.old_spte))
+		if (!is_shadow_present_pte(iter.old_spte) ||
+		    iter.old_spte & shadow_dirty_mask)
 			continue;
 
 		new_spte = iter.old_spte | shadow_dirty_mask;
-- 
2.30.0.365.g02bc693789-goog