linux-kernel - [PATCH 2/5] KVM: MMU: simplify mmu_set

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Date:	Mon, 05 Nov 2012 20:10:08 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: [PATCH 2/5] KVM: MMU: simplify mmu_set_spte

In order to detecting spte remapping, we can simply check whether the
spte has already been pointing to the pfn even if the spte is not the
last spte for middle spte is pointing to the kernel pfn which can not
be mapped to userspace

Also, update slot and stat.lpages iff the spte is not remapped

Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
---
 arch/x86/kvm/mmu.c |   40 +++++++++++++---------------------------
 1 files changed, 13 insertions(+), 27 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 692ebb1..4ea731e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2420,8 +2420,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 			 pfn_t pfn, bool speculative,
 			 bool host_writable)
 {
-	int was_rmapped = 0;
-	int rmap_count;
+	bool was_rmapped = false;

 	pgprintk("%s: spte %llx access %x write_fault %d"
 		 " user_fault %d gfn %llx\n",
@@ -2429,25 +2428,13 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		 write_fault, user_fault, gfn);

 	if (is_rmap_spte(*sptep)) {
-		/*
-		 * If we overwrite a PTE page pointer with a 2MB PMD, unlink
-		 * the parent of the now unreachable PTE.
-		 */
-		if (level > PT_PAGE_TABLE_LEVEL &&
-		    !is_large_pte(*sptep)) {
-			struct kvm_mmu_page *child;
-			u64 pte = *sptep;
+		if (pfn != spte_to_pfn(*sptep)) {
+			struct kvm_mmu_page *sp = page_header(__pa(sptep));

-			child = page_header(pte & PT64_BASE_ADDR_MASK);
-			drop_parent_pte(child, sptep);
-			kvm_flush_remote_tlbs(vcpu->kvm);
-		} else if (pfn != spte_to_pfn(*sptep)) {
-			pgprintk("hfn old %llx new %llx\n",
-				 spte_to_pfn(*sptep), pfn);
-			drop_spte(vcpu->kvm, sptep);
-			kvm_flush_remote_tlbs(vcpu->kvm);
+			if (mmu_page_zap_pte(vcpu->kvm, sp, sptep))
+				kvm_flush_remote_tlbs(vcpu->kvm);
 		} else
-			was_rmapped = 1;
+			was_rmapped = true;
 	}

 	if (set_spte(vcpu, sptep, pte_access, user_fault, write_fault,
@@ -2466,16 +2453,15 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		 is_large_pte(*sptep)? "2MB" : "4kB",
 		 *sptep & PT_PRESENT_MASK ?"RW":"R", gfn,
 		 *sptep, sptep);
-	if (!was_rmapped && is_large_pte(*sptep))
-		++vcpu->kvm->stat.lpages;

-	if (is_shadow_present_pte(*sptep)) {
+	if (is_shadow_present_pte(*sptep) && !was_rmapped) {
+		if (is_large_pte(*sptep))
+			++vcpu->kvm->stat.lpages;
+
 		page_header_update_slot(vcpu->kvm, sptep, gfn);
-		if (!was_rmapped) {
-			rmap_count = rmap_add(vcpu, sptep, gfn);
-			if (rmap_count > RMAP_RECYCLE_THRESHOLD)
-				rmap_recycle(vcpu, sptep, gfn);
-		}
+
+		if (rmap_add(vcpu, sptep, gfn) > RMAP_RECYCLE_THRESHOLD)
+			rmap_recycle(vcpu, sptep, gfn);
 	}

 	kvm_release_pfn_clean(pfn);
-- 
1.7.7.6

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