From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT, so it is saved/restored
each time during world switch. Jim from Google pointed out that
when running schbench in L2, vmx_vcpu_run will occupy 4% cpu time,
and the 25% of vmx_vcpu_run cpu time is occupied by get_debugctlmsr().
This patch caches the host IA32_DEBUGCTL MSR and saves/restores
the host IA32_DEBUGCTL msr when guest/host switches to avoid to
save/restore each time during world switch.
Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: Jim Mattson <jmattson@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/vmx.c | 11 +++++------
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 63d34bc..c904250 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -619,6 +619,7 @@ struct kvm_vcpu_arch {
unsigned long dr7;
unsigned long eff_db[KVM_NR_DB_REGS];
unsigned long guest_debug_dr7;
+ unsigned long debugctlmsr;
u64 msr_platform_info;
u64 msr_misc_features_enables;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8c7e816..b167bba 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2326,6 +2326,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vmx_vcpu_pi_load(vcpu, cpu);
vmx->host_pkru = read_pkru();
+ vcpu->arch.debugctlmsr = get_debugctlmsr();
}
static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
@@ -2347,6 +2348,9 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
vmx_vcpu_pi_put(vcpu);
__vmx_load_host_state(to_vmx(vcpu));
+ /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
+ if (vcpu->arch.debugctlmsr)
+ update_debugctlmsr(vcpu->arch.debugctlmsr);
}
static bool emulation_required(struct kvm_vcpu *vcpu)
@@ -9346,7 +9350,7 @@ static void vmx_arm_hv_timer(struct kvm_vcpu *vcpu)
static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- unsigned long debugctlmsr, cr3, cr4;
+ unsigned long cr3, cr4;
/* Record the guest's net vcpu time for enforced NMI injections. */
if (unlikely(!enable_vnmi &&
@@ -9399,7 +9403,6 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
__write_pkru(vcpu->arch.pkru);
atomic_switch_perf_msrs(vmx);
- debugctlmsr = get_debugctlmsr();
vmx_arm_hv_timer(vcpu);
@@ -9509,10 +9512,6 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
#endif
);
- /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
- if (debugctlmsr)
- update_debugctlmsr(debugctlmsr);
-
#ifndef CONFIG_X86_64
/*
* The sysexit path does not restore ds/es, so we must set them to
--
2.7.4
