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Subject[PATCH v2 27/32] KVM: nVMX: Reload APIC access page on nested VM-Exit only if necessary
Date
Defer reloading L1's APIC page by logging the need for a reload and
processing it during nested VM-Exit instead of unconditionally reloading
the APIC page on nested VM-Exit. This eliminates a TLB flush on the
majority of VM-Exits as the APIC page rarely needs to be reloaded.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/nested.c | 9 ++++-----
arch/x86/kvm/vmx/vmx.c | 10 +++++++---
arch/x86/kvm/vmx/vmx.h | 1 +
3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 04cdf7ded1d3..d816f1366943 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4365,11 +4365,10 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map, true);
vmx->nested.pi_desc = NULL;

- /*
- * We are now running in L2, mmu_notifier will force to reload the
- * page's hpa for L2 vmcs. Need to reload it for L1 before entering L1.
- */
- kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
+ if (vmx->nested.reload_vmcs01_apic_access_page) {
+ vmx->nested.reload_vmcs01_apic_access_page = false;
+ kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
+ }

if ((exit_reason != -1) && (enable_shadow_vmcs || vmx->nested.hv_evmcs))
vmx->nested.need_vmcs12_to_shadow_sync = true;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ae7279802652..3155329bf844 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6138,10 +6138,14 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)

static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu, hpa_t hpa)
{
- if (!is_guest_mode(vcpu)) {
- vmcs_write64(APIC_ACCESS_ADDR, hpa);
- vmx_flush_tlb_current(vcpu);
+ /* Defer reload until vmcs01 is the current VMCS. */
+ if (is_guest_mode(vcpu)) {
+ to_vmx(vcpu)->nested.reload_vmcs01_apic_access_page = true;
+ return;
}
+
+ vmcs_write64(APIC_ACCESS_ADDR, hpa);
+ vmx_flush_tlb_current(vcpu);
}

static void vmx_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 571249e18bb6..66cc9f639e4b 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -138,6 +138,7 @@ struct nested_vmx {
bool vmcs02_initialized;

bool change_vmcs01_virtual_apic_mode;
+ bool reload_vmcs01_apic_access_page;

/*
* Enlightened VMCS has been enabled. It does not mean that L1 has to
--
2.24.1
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