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    Subject[PATCH v3 27/37] 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 e630d656b211..06fc0b68ecf3 100644
    --- a/arch/x86/kvm/vmx/nested.c
    +++ b/arch/x86/kvm/vmx/nested.c
    @@ -4367,11 +4367,10 @@ 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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