KVM: VMX: Cache IA32_DEBUGCTL in memory

MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT, so it is saved/restored each
time during world switch.  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.  This saves
about 100 clock cycles per vmexit.

Suggested-by: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3b5f702..4e7da90 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -650,6 +650,8 @@ struct vcpu_vmx {
 
        u32 host_pkru;
 
+       unsigned long host_debugctlmsr;
+
        /*
         * Only bits masked by msr_ia32_feature_control_valid_bits can be set in
         * msr_ia32_feature_control. FEATURE_CONTROL_LOCKED is always included
@@ -2318,6 +2320,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
        vmx_vcpu_pi_load(vcpu, cpu);
        vmx->host_pkru = read_pkru();
+       vmx->host_debugctlmsr = get_debugctlmsr();
 }
 
 static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
@@ -9261,7 +9264,7 @@ 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 &&
@@ -9314,7 +9317,6 @@ 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);
 
@@ -9425,8 +9427,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
              );
 
        /* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
-       if (debugctlmsr)
-               update_debugctlmsr(debugctlmsr);
+       if (vmx->host_debugctlmsr)
+               update_debugctlmsr(vmx->host_debugctlmsr);
 
 #ifndef CONFIG_X86_64
        /*