KVM: SVM: Only save/restore MSRs when needed
We only have to save/restore MSR_GS_BASE on every VMEXIT. The rest can be
saved/restored when we leave the VCPU. Since we don't emulate the DEBUGCTL
MSRs and the guest cannot write to them, we don't have to worry about
saving/restoring them at all.
This shaves a whopping 40% off raw vmexit costs on AMD.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/kvm_svm.h b/drivers/kvm/kvm_svm.h
index a1a9eba..a869983 100644
--- a/drivers/kvm/kvm_svm.h
+++ b/drivers/kvm/kvm_svm.h
@@ -9,17 +9,15 @@
#include "svm.h"
#include "kvm.h"
-static const u32 host_save_msrs[] = {
+static const u32 host_save_user_msrs[] = {
#ifdef CONFIG_X86_64
MSR_STAR, MSR_LSTAR, MSR_CSTAR, MSR_SYSCALL_MASK, MSR_KERNEL_GS_BASE,
- MSR_FS_BASE, MSR_GS_BASE,
+ MSR_FS_BASE,
#endif
MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
- MSR_IA32_DEBUGCTLMSR, /*MSR_IA32_LASTBRANCHFROMIP,
- MSR_IA32_LASTBRANCHTOIP, MSR_IA32_LASTINTFROMIP,MSR_IA32_LASTINTTOIP,*/
};
-#define NR_HOST_SAVE_MSRS ARRAY_SIZE(host_save_msrs)
+#define NR_HOST_SAVE_USER_MSRS ARRAY_SIZE(host_save_user_msrs)
#define NUM_DB_REGS 4
struct vcpu_svm {
@@ -32,7 +30,8 @@
u64 next_rip;
- u64 host_msrs[NR_HOST_SAVE_MSRS];
+ u64 host_user_msrs[NR_HOST_SAVE_USER_MSRS];
+ u64 host_gs_base;
unsigned long host_cr2;
unsigned long host_db_regs[NUM_DB_REGS];
unsigned long host_dr6;
diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index bddd023..9c15f32 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -522,8 +522,6 @@
control->msrpm_base_pa = msrpm_base;
control->tsc_offset = 0;
control->int_ctl = V_INTR_MASKING_MASK;
- if (svm_has(SVM_FEATURE_LBRV))
- control->lbr_ctl = 1ULL;
init_seg(&save->es);
init_seg(&save->ss);
@@ -611,7 +609,7 @@
static void svm_vcpu_load(struct kvm_vcpu *vcpu)
{
- int cpu;
+ int cpu, i;
cpu = get_cpu();
if (unlikely(cpu != vcpu->cpu)) {
@@ -626,10 +624,18 @@
vcpu->svm->vmcb->control.tsc_offset += delta;
vcpu->cpu = cpu;
}
+
+ for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+ rdmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);
}
static void svm_vcpu_put(struct kvm_vcpu *vcpu)
{
+ int i;
+
+ for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+ wrmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);
+
rdtscll(vcpu->host_tsc);
put_cpu();
}
@@ -815,18 +821,16 @@
static void load_host_msrs(struct kvm_vcpu *vcpu)
{
- int i;
-
- for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)
- wrmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);
+#ifdef CONFIG_X86_64
+ wrmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);
+#endif
}
static void save_host_msrs(struct kvm_vcpu *vcpu)
{
- int i;
-
- for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)
- rdmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);
+#ifdef CONFIG_X86_64
+ rdmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);
+#endif
}
static void new_asid(struct kvm_vcpu *vcpu, struct svm_cpu_data *svm_data)
