[PATCH v3 2/2] KVM: Fetch guest cr3 from hardware on demand

Avi Kivity
2010-12-22T14:21:07Z

Instead of syncing the guest cr3 every exit, which is expensince on vmx
with ept enabled, sync it only on demand.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/kvm_cache_regs.h | 2 ++
arch/x86/kvm/svm.c | 5 +++++
arch/x86/kvm/vmx.c | 22 ++++++++++++++++------
arch/x86/kvm/x86.c | 2 ++
5 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4461429..07a20f4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -117,6 +117,7 @@ enum kvm_reg {

enum kvm_reg_ex {
VCPU_EXREG_PDPTR = NR_VCPU_REGS,
+ VCPU_EXREG_CR3,
};

enum {
@@ -533,6 +534,7 @@ struct kvm_x86_ops {
struct kvm_segment *var, int seg);
void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
void (*decache_cr0_guest_bits)(struct kvm_vcpu *vcpu);
+ void (*decache_cr3)(struct kvm_vcpu *vcpu);
void (*decache_cr4_guest_bits)(struct kvm_vcpu *vcpu);
void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
void (*set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index a6bf8db..3377d53 100644
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -75,6 +75,8 @@ static inline ulong kvm_read_cr4_bits(struct kvm_vcpu *vcpu, ulong mask)

static inline ulong kvm_read_cr3(struct kvm_vcpu *vcpu)
{
+ if (!test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
+ kvm_x86_ops->decache_cr3(vcpu);
return vcpu->arch.cr3;
}

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5d0f945..78d13de 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1323,6 +1323,10 @@ static void svm_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
{
}

+static void svm_decache_cr3(struct kvm_vcpu *vcpu)
+{
+}
+
static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
}
@@ -3765,6 +3769,7 @@ static struct kvm_x86_ops svm_x86_ops = {
.get_cpl = svm_get_cpl,
.get_cs_db_l_bits = kvm_get_cs_db_l_bits,
.decache_cr0_guest_bits = svm_decache_cr0_guest_bits,
+ .decache_cr3 = svm_decache_cr3,
.decache_cr4_guest_bits = svm_decache_cr4_guest_bits,
.set_cr0 = svm_set_cr0,
.set_cr3 = svm_set_cr3,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fb09685..a620336 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -180,6 +180,7 @@ static int init_rmode(struct kvm *kvm);
static u64 construct_eptp(unsigned long root_hpa);
static void kvm_cpu_vmxon(u64 addr);
static void kvm_cpu_vmxoff(void);
+static void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);

static DEFINE_PER_CPU(struct vmcs *, vmxarea);
static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
@@ -1836,6 +1837,13 @@ static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu)
vcpu->arch.cr0 |= vmcs_readl(GUEST_CR0) & cr0_guest_owned_bits;
}

+static void vmx_decache_cr3(struct kvm_vcpu *vcpu)
+{
+ if (enable_ept && is_paging(vcpu))
+ vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
+ __set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
+}
+
static void vmx_decache_cr4_guest_bits(struct kvm_vcpu *vcpu)
{
ulong cr4_guest_owned_bits = vcpu->arch.cr4_guest_owned_bits;
@@ -1879,6 +1887,8 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
unsigned long cr0,
struct kvm_vcpu *vcpu)
{
+ ulong cr3;
+
if (!(cr0 & X86_CR0_PG)) {
/* From paging/starting to nonpaging */
vmcs_write32(CPU_BASED_VM_EXEC_CONTROL,
@@ -1893,8 +1903,11 @@ static void ept_update_paging_mode_cr0(unsigned long *hw_cr0,
vmcs_read32(CPU_BASED_VM_EXEC_CONTROL) &
~(CPU_BASED_CR3_LOAD_EXITING |
CPU_BASED_CR3_STORE_EXITING));
+ /* Must fetch cr3 before updating cr0 */
+ cr3 = kvm_read_cr3(vcpu);
vcpu->arch.cr0 = cr0;
vmx_set_cr4(vcpu, kvm_read_cr4(vcpu));
+ vmx_set_cr3(vcpu, cr3);
}

if (!(cr0 & X86_CR0_WP))
@@ -3734,11 +3747,6 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
if (vmx->emulation_required && emulate_invalid_guest_state)
return handle_invalid_guest_state(vcpu);

- /* Access CR3 don't cause VMExit in paging mode, so we need
- * to sync with guest real CR3. */
- if (enable_ept && is_paging(vcpu))
- vcpu->arch.cr3 = vmcs_readl(GUEST_CR3);
-
if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
vcpu->run->fail_entry.hardware_entry_failure_reason
@@ -4055,7 +4063,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
);

vcpu->arch.regs_avail = ~((1 << VCPU_REGS_RIP) | (1 << VCPU_REGS_RSP)
- | (1 << VCPU_EXREG_PDPTR));
+ | (1 << VCPU_EXREG_PDPTR)
+ | (1 << VCPU_EXREG_CR3));
vcpu->arch.regs_dirty = 0;

vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
@@ -4322,6 +4331,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
.get_cpl = vmx_get_cpl,
.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
.decache_cr0_guest_bits = vmx_decache_cr0_guest_bits,
+ .decache_cr3 = vmx_decache_cr3,
.decache_cr4_guest_bits = vmx_decache_cr4_guest_bits,
.set_cr0 = vmx_set_cr0,
.set_cr3 = vmx_set_cr3,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c9c0077..a0e2f39 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -658,6 +658,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
if (unlikely(!gfn_to_memslot(vcpu->kvm, cr3 >> PAGE_SHIFT)))
return 1;
vcpu->arch.cr3 = cr3;
+ __set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);
vcpu->arch.mmu.new_cr3(vcpu);
return 0;
}
@@ -5575,6 +5576,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
vcpu->arch.cr2 = sregs->cr2;
mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
vcpu->arch.cr3 = sregs->cr3;
+ __set_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail);

kvm_set_cr8(vcpu, sregs->cr8);

--
1.7.1