linux-kernel - [PATCH] KVM: x86: always set accessed bit in shadow PTEs

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Date:	Fri, 13 Nov 2015 11:58:22 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	Yang Zhang <yang.z.zhang@...el.com>,
	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
Subject: [PATCH] KVM: x86: always set accessed bit in shadow PTEs

Commit 7a1638ce4220 ("nEPT: Redefine EPT-specific link_shadow_page()",
2013-08-05) says:

    Since nEPT doesn't support A/D bit, we should not set those bit
    when building the shadow page table.

but this is not necessary.  Even though nEPT doesn't support A/D
bits, and hence the vmcs12 EPT pointer will never enable them,
we always use them for shadow page tables if available (see
construct_eptp in vmx.c).  So we can set the A/D bits freely
in the shadow page table.

This patch hence basically reverts commit 7a1638ce4220.

Cc: Yang Zhang <yang.z.zhang@...el.com>
Cc: Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu.c         | 9 +++------
 arch/x86/kvm/paging_tmpl.h | 4 ++--
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d31b55d1fd5c..ec4e0218ab0a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2195,7 +2195,7 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator)
 }
 
 static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
-			     struct kvm_mmu_page *sp, bool accessed)
+			     struct kvm_mmu_page *sp)
 {
 	u64 spte;
 
@@ -2203,10 +2203,7 @@ static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
 			VMX_EPT_WRITABLE_MASK != PT_WRITABLE_MASK);
 
 	spte = __pa(sp->spt) | PT_PRESENT_MASK | PT_WRITABLE_MASK |
-	       shadow_user_mask | shadow_x_mask;
-
-	if (accessed)
-		spte |= shadow_accessed_mask;
+	       shadow_user_mask | shadow_x_mask | shadow_accessed_mask;
 
 	mmu_spte_set(sptep, spte);
 
@@ -2736,7 +2733,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, int write, int map_writable,
 			sp = kvm_mmu_get_page(vcpu, pseudo_gfn, iterator.addr,
 					      iterator.level - 1, 1, ACC_ALL);
 
-			link_shadow_page(vcpu, iterator.sptep, sp, true);
+			link_shadow_page(vcpu, iterator.sptep, sp);
 		}
 	}
 	return emulate;
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index ee9d21115535..91e939b486d1 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -598,7 +598,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 			goto out_gpte_changed;
 
 		if (sp)
-			link_shadow_page(vcpu, it.sptep, sp, PT_GUEST_ACCESSED_MASK);
+			link_shadow_page(vcpu, it.sptep, sp);
 	}
 
 	for (;
@@ -618,7 +618,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
 
 		sp = kvm_mmu_get_page(vcpu, direct_gfn, addr, it.level-1,
 				      true, direct_access);
-		link_shadow_page(vcpu, it.sptep, sp, PT_GUEST_ACCESSED_MASK);
+		link_shadow_page(vcpu, it.sptep, sp);
 	}
 
 	clear_sp_write_flooding_count(it.sptep);
-- 
1.8.3.1

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