linux-kernel - [PATCH 2/2] KVM MMU: record reverse mapping for spte only if it's writable

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Date:	Thu, 01 Apr 2010 16:52:50 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/2] KVM MMU: record reverse mapping for spte only if it's
 writable

The read only spte mapping can't hurt shadow page cache,
so, no need to record it.

Using bit9 to record whether the spte is re-mapped

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/mmu.c |   17 +++++++++++++++--
 arch/x86/kvm/mmu.h |    1 +
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5de92ae..999f572 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -259,7 +259,17 @@ static int is_dirty_gpte(unsigned long pte)
 
 static int is_rmap_spte(u64 pte)
 {
-	return is_shadow_present_pte(pte);
+	return pte & PT_RMAP_MASK;
+}
+
+static void spte_set_rmap(u64 *spte)
+{
+	*spte |= PT_RMAP_MASK;
+}
+
+static void spte_clear_rmap(u64 *spte)
+{
+	*spte &= ~PT_RMAP_MASK;
 }
 
 static int is_last_spte(u64 pte, int level)
@@ -543,7 +553,7 @@ static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
 	unsigned long *rmapp;
 	int i, count = 0;
 
-	if (!is_rmap_spte(*spte))
+	if (!is_shadow_present_pte(*spte) || !is_writable_pte(*spte))
 		return count;
 	gfn = unalias_gfn(vcpu->kvm, gfn);
 	sp = page_header(__pa(spte));
@@ -573,6 +583,7 @@ static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
 			;
 		desc->sptes[i] = spte;
 	}
+	spte_set_rmap(spte);
 	return count;
 }
 
@@ -610,6 +621,7 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
 
 	if (!is_rmap_spte(*spte))
 		return;
+	spte_clear_rmap(spte);
 	sp = page_header(__pa(spte));
 	pfn = spte_to_pfn(*spte);
 	if (*spte & shadow_accessed_mask)
@@ -646,6 +658,7 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
 		pr_err("rmap_remove: %p %llx many->many\n", spte, *spte);
 		BUG();
 	}
+
 }
 
 static u64 *rmap_next(struct kvm *kvm, unsigned long *rmapp, u64 *spte)
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index be66759..166b9b5 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -22,6 +22,7 @@
 #define PT_PAGE_SIZE_MASK (1ULL << 7)
 #define PT_PAT_MASK (1ULL << 7)
 #define PT_GLOBAL_MASK (1ULL << 8)
+#define PT_RMAP_MASK (1ULL << 9)
 #define PT64_NX_SHIFT 63
 #define PT64_NX_MASK (1ULL << PT64_NX_SHIFT)
 
-- 
1.6.1.2





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