linux-kernel - [PATCH 1/3] KVM: x86: remove unnecessary rmap walk of read-only memslots

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Date:   Tue,  2 Jun 2020 13:07:28 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        steven.sistare@...cle.com, anthony.yznaga@...cle.com
Subject: [PATCH 1/3] KVM: x86: remove unnecessary rmap walk of read-only memslots

There's no write access to remove.  An existing memslot cannot be updated
to set or clear KVM_MEM_READONLY, and any mappings established in a newly
created or moved read-only memslot will already be read-only.

Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 arch/x86/kvm/x86.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c17e6eb9ad43..23fd888e52ee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10038,11 +10038,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
 				     struct kvm_memory_slot *new)
 {
-	/* Still write protect RO slot */
-	if (new->flags & KVM_MEM_READONLY) {
-		kvm_mmu_slot_remove_write_access(kvm, new, PT_PAGE_TABLE_LEVEL);
+	/* Nothing to do for RO slots */
+	if (new->flags & KVM_MEM_READONLY)
 		return;
-	}
 
 	/*
 	 * Call kvm_x86_ops dirty logging hooks when they are valid.
-- 
2.13.3