[PATCH 1/2] KVM: nVMX: Refactor IBPB handling on VMCS switch to genericize code

From: Sean Christopherson
Date: Wed May 06 2020 - 19:58:57 EST


Refactor the IPBP handling to effectively move the WARN and comment in
vmx_switch_vmcs() to vmx_vcpu_load_vmcs(). A future patch will give
copy_vmcs02_to_vmcs12_rare() the same treatment.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx/nested.c | 9 +--------
arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++----
arch/x86/kvm/vmx/vmx.h | 3 ++-
3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 20a9edca51fa5..7d1e19149ef46 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -302,15 +302,8 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)

cpu = get_cpu();
prev = vmx->loaded_vmcs;
- WARN_ON_ONCE(prev->cpu != cpu || prev->vmcs != per_cpu(current_vmcs, cpu));
vmx->loaded_vmcs = vmcs;
-
- /*
- * This is the same guest from our point of view, so no
- * indirect branch prediction barrier is needed. The L1
- * guest can protect itself with retpolines, IBPB or IBRS.
- */
- vmx_vcpu_load_vmcs(vcpu, cpu, false);
+ vmx_vcpu_load_vmcs(vcpu, cpu, prev);
vmx_sync_vmcs_host_state(vmx, prev);
put_cpu();

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 94f49c5ae89aa..ddbd8fae24927 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1311,10 +1311,12 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
pi_set_on(pi_desc);
}

-void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool need_ibpb)
+void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
+ struct loaded_vmcs *buddy)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
bool already_loaded = vmx->loaded_vmcs->cpu == cpu;
+ struct vmcs *prev;

if (!already_loaded) {
loaded_vmcs_clear(vmx->loaded_vmcs);
@@ -1333,10 +1335,17 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool need_ibpb)
local_irq_enable();
}

- if (per_cpu(current_vmcs, cpu) != vmx->loaded_vmcs->vmcs) {
+ prev = per_cpu(current_vmcs, cpu);
+ if (prev != vmx->loaded_vmcs->vmcs) {
per_cpu(current_vmcs, cpu) = vmx->loaded_vmcs->vmcs;
vmcs_load(vmx->loaded_vmcs->vmcs);
- if (need_ibpb)
+
+ /*
+ * No indirect branch prediction barrier needed when switching
+ * the active VMCS within a guest, e.g. on nested VM-Enter.
+ * The L1 VMM can protect itself with retpolines, IBPB or IBRS.
+ */
+ if (!buddy || WARN_ON_ONCE(buddy->vmcs != prev))
indirect_branch_prediction_barrier();
}

@@ -1378,7 +1387,7 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- vmx_vcpu_load_vmcs(vcpu, cpu, true);
+ vmx_vcpu_load_vmcs(vcpu, cpu, NULL);

vmx_vcpu_pi_load(vcpu, cpu);

diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index c6f940ba5d79c..4a6f382b05b49 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -320,7 +320,8 @@ struct kvm_vmx {
};

bool nested_vmx_allowed(struct kvm_vcpu *vcpu);
-void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu, bool need_ibpb);
+void vmx_vcpu_load_vmcs(struct kvm_vcpu *vcpu, int cpu,
+ struct loaded_vmcs *buddy);
void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
int allocate_vpid(void);
void free_vpid(int vpid);
--
2.26.0