[PATCH 07/15] KVM: nVMX: Don't reread VMCS-agnostic state when switching VMCS

Sean Christopherson
2019-05-07T16:07:08Z

When switching between vmcs01 and vmcs02, there is no need to update
state tracking for values that aren't tied to any particular VMCS as
the per-vCPU values are already up-to-date (vmx_switch_vmcs() can only
be called when the vCPU is loaded).

Avoiding the update eliminates a RDMSR, and potentially a RDPKRU and
posted-interrupt updated (cmpxchg64() and more).

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/nested.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 18 +++++++++++++-----
arch/x86/kvm/vmx/vmx.h | 2 +-
3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4651d3462df4..99164d054922 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -251,7 +251,7 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
cpu = get_cpu();
prev = vmx->loaded_cpu_state;
vmx->loaded_vmcs = vmcs;
- vmx_vcpu_load(vcpu, cpu);
+ __vmx_vcpu_load(vcpu, cpu);

if (likely(prev)) {
src = &prev->host_state;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b97666731425..0c48dee4159b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1231,11 +1231,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
pi_set_on(pi_desc);
}

-/*
- * Switches to specified vcpu, until a matching vcpu_put(), but assumes
- * vcpu mutex is already taken.
- */
-void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+void __vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
bool already_loaded = vmx->loaded_vmcs->cpu == cpu;
@@ -1296,8 +1292,20 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
if (kvm_has_tsc_control &&
vmx->current_tsc_ratio != vcpu->arch.tsc_scaling_ratio)
decache_tsc_multiplier(vmx);
+}
+
+/*
+ * Switches to specified vcpu, until a matching vcpu_put(), but assumes
+ * vcpu mutex is already taken.
+ */
+static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+ __vmx_vcpu_load(vcpu, cpu);

vmx_vcpu_pi_load(vcpu, cpu);
+
vmx->host_pkru = read_pkru();
vmx->host_debugctlmsr = get_debugctlmsr();
}
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index f81b32ae1822..f62a008c9227 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -292,7 +292,7 @@ struct kvm_vmx {
};

bool nested_vmx_allowed(struct kvm_vcpu *vcpu);
-void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
+void __vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
int allocate_vpid(void);
void free_vpid(int vpid);
void vmx_set_constant_host_state(struct vcpu_vmx *vmx);
--
2.21.0