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authorAvi Kivity <avi@qumranet.com>2007-04-19 13:22:48 +0300
committerAvi Kivity <avi@qumranet.com>2007-05-03 10:52:30 +0300
commite38aea3e9330624d19a233c05f3e69c57519edd5 (patch)
tree68daabdafa535043ab68d01b80642fbf6a4c0977
parent2345df8c555ecb92c0c36172c07d5ac321a92dc7 (diff)
KVM: VMX: Don't switch 64-bit msrs for 32-bit guests
Some msrs are only used by x86_64 instructions, and are therefore not needed when the guest is legacy mode. By not bothering to switch them, we reduce vmexit latency by 2400 cycles (from about 8800) when running a 32-bt guest on a 64-bit host. Signed-off-by: Avi Kivity <avi@qumranet.com>
-rw-r--r--drivers/kvm/vmx.c58
1 files changed, 42 insertions, 16 deletions
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 3745e6ccc5b..6270df58e05 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -80,6 +80,9 @@ static const u32 vmx_msr_index[] = {
#ifdef CONFIG_X86_64
static unsigned msr_offset_kernel_gs_base;
+#define NR_64BIT_MSRS 4
+#else
+#define NR_64BIT_MSRS 0
#endif
static inline int is_page_fault(u32 intr_info)
@@ -301,6 +304,32 @@ static void vmx_inject_gp(struct kvm_vcpu *vcpu, unsigned error_code)
}
/*
+ * Set up the vmcs to automatically save and restore system
+ * msrs. Don't touch the 64-bit msrs if the guest is in legacy
+ * mode, as fiddling with msrs is very expensive.
+ */
+static void setup_msrs(struct kvm_vcpu *vcpu)
+{
+ int nr_skip, nr_good_msrs;
+
+ if (is_long_mode(vcpu))
+ nr_skip = NR_BAD_MSRS;
+ else
+ nr_skip = NR_64BIT_MSRS;
+ nr_good_msrs = vcpu->nmsrs - nr_skip;
+
+ vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR,
+ virt_to_phys(vcpu->guest_msrs + nr_skip));
+ vmcs_writel(VM_EXIT_MSR_STORE_ADDR,
+ virt_to_phys(vcpu->guest_msrs + nr_skip));
+ vmcs_writel(VM_EXIT_MSR_LOAD_ADDR,
+ virt_to_phys(vcpu->host_msrs + nr_skip));
+ vmcs_write32(VM_EXIT_MSR_STORE_COUNT, nr_good_msrs); /* 22.2.2 */
+ vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */
+ vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */
+}
+
+/*
* reads and returns guest's timestamp counter "register"
* guest_tsc = host_tsc + tsc_offset -- 21.3
*/
@@ -825,6 +854,7 @@ static void vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
msr->data = efer & ~EFER_LME;
}
+ setup_msrs(vcpu);
}
#endif
@@ -988,7 +1018,6 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu)
struct descriptor_table dt;
int i;
int ret = 0;
- int nr_good_msrs;
extern asmlinkage void kvm_vmx_return(void);
if (!init_rmode_tss(vcpu->kvm)) {
@@ -1140,19 +1169,10 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu)
++vcpu->nmsrs;
}
- nr_good_msrs = vcpu->nmsrs - NR_BAD_MSRS;
- vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR,
- virt_to_phys(vcpu->guest_msrs + NR_BAD_MSRS));
- vmcs_writel(VM_EXIT_MSR_STORE_ADDR,
- virt_to_phys(vcpu->guest_msrs + NR_BAD_MSRS));
- vmcs_writel(VM_EXIT_MSR_LOAD_ADDR,
- virt_to_phys(vcpu->host_msrs + NR_BAD_MSRS));
+ setup_msrs(vcpu);
+
vmcs_write32_fixedbits(MSR_IA32_VMX_EXIT_CTLS, VM_EXIT_CONTROLS,
(HOST_IS_64 << 9)); /* 22.2,1, 20.7.1 */
- vmcs_write32(VM_EXIT_MSR_STORE_COUNT, nr_good_msrs); /* 22.2.2 */
- vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */
- vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */
-
/* 22.2.1, 20.8.1 */
vmcs_write32_fixedbits(MSR_IA32_VMX_ENTRY_CTLS,
@@ -1769,9 +1789,11 @@ again:
fx_restore(vcpu->guest_fx_image);
#ifdef CONFIG_X86_64
- save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1);
+ if (is_long_mode(vcpu)) {
+ save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1);
+ load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
+ }
#endif
- load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
asm (
/* Store host registers */
@@ -1915,8 +1937,12 @@ again:
}
++kvm_stat.exits;
- save_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
- load_msrs(vcpu->host_msrs, NR_BAD_MSRS);
+#ifdef CONFIG_X86_64
+ if (is_long_mode(vcpu)) {
+ save_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
+ load_msrs(vcpu->host_msrs, NR_BAD_MSRS);
+ }
+#endif
fx_save(vcpu->guest_fx_image);
fx_restore(vcpu->host_fx_image);