[PATCH 4/4] VMX: x86: Only reset MMU when necessary

[Sheng Yang <sheng@xxxxxxxxxxxxxxx>]

Only modifying some bits of CR0/CR4 needs paging mode switch.

Add update_rsvd_bits_mask() to address EFER.NX bit updating for reserved bits.

Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |    1 +
 arch/x86/kvm/mmu.c              |   17 ++++++++++++++---
 arch/x86/kvm/x86.c              |   15 +++++++++++++--
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ed48904..c8c8a03 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -553,6 +553,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
 void kvm_mmu_zap_all(struct kvm *kvm);
 unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
+void update_rsvd_bits_mask(struct kvm_vcpu *vcpu);
 
 int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3);
 
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5412185..98abdcf 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2335,6 +2335,19 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
 	}
 }
 
+void update_rsvd_bits_mask(struct kvm_vcpu *vcpu)
+{
+	if (!is_paging(vcpu))
+		return;
+	if (is_long_mode(vcpu))
+		reset_rsvds_bits_mask(vcpu, PT64_ROOT_LEVEL);
+	else if (is_pae(vcpu))
+		reset_rsvds_bits_mask(vcpu, PT32E_ROOT_LEVEL);
+	else
+		reset_rsvds_bits_mask(vcpu, PT32_ROOT_LEVEL);
+}
+EXPORT_SYMBOL_GPL(update_rsvd_bits_mask);
+
 static int paging64_init_context_common(struct kvm_vcpu *vcpu, int level)
 {
 	struct kvm_mmu *context = &vcpu->arch.mmu;
@@ -2400,18 +2413,16 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 		context->gva_to_gpa = nonpaging_gva_to_gpa;
 		context->root_level = 0;
 	} else if (is_long_mode(vcpu)) {
-		reset_rsvds_bits_mask(vcpu, PT64_ROOT_LEVEL);
 		context->gva_to_gpa = paging64_gva_to_gpa;
 		context->root_level = PT64_ROOT_LEVEL;
 	} else if (is_pae(vcpu)) {
-		reset_rsvds_bits_mask(vcpu, PT32E_ROOT_LEVEL);
 		context->gva_to_gpa = paging64_gva_to_gpa;
 		context->root_level = PT32E_ROOT_LEVEL;
 	} else {
-		reset_rsvds_bits_mask(vcpu, PT32_ROOT_LEVEL);
 		context->gva_to_gpa = paging32_gva_to_gpa;
 		context->root_level = PT32_ROOT_LEVEL;
 	}
+	update_rsvd_bits_mask(vcpu);
 
 	return 0;
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b59fc67..971a295 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -416,6 +416,10 @@ out:
 
 static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
+	unsigned long old_cr0 = kvm_read_cr0(vcpu);
+	unsigned long update_bits = X86_CR0_PG | X86_CR0_PE |
+				    X86_CR0_CD | X86_CR0_NW;
+
 	cr0 |= X86_CR0_ET;
 
 #ifdef CONFIG_X86_64
@@ -449,7 +453,8 @@ static int __kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 
 	kvm_x86_ops->set_cr0(vcpu, cr0);
 
-	kvm_mmu_reset_context(vcpu);
+	if ((cr0 ^ old_cr0) & update_bits)
+		kvm_mmu_reset_context(vcpu);
 	return 0;
 }
 
@@ -487,7 +492,8 @@ int __kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 
 	kvm_x86_ops->set_cr4(vcpu, cr4);
 
-	kvm_mmu_reset_context(vcpu);
+	if ((cr4 ^ old_cr4) & pdptr_bits)
+		kvm_mmu_reset_context(vcpu);
 
 	return 0;
 }
@@ -692,6 +698,8 @@ static u32 emulated_msrs[] = {
 
 static int set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
+	u64 old_efer = vcpu->arch.efer;
+
 	if (efer & efer_reserved_bits)
 		return 1;
 
@@ -722,6 +730,9 @@ static int set_efer(struct kvm_vcpu *vcpu, u64 efer)
 
 	vcpu->arch.mmu.base_role.nxe = (efer & EFER_NX) && !tdp_enabled;
 
+	if ((efer ^ old_efer) & EFER_NX)
+		update_rsvd_bits_mask(vcpu);
+
 	return 0;
 }
 
-- 
1.7.0.1

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