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Date: Wed, 3 Sep 2014 18:08:36 +0300
From: Gleb Natapov <gleb@...nel.org>
To: Tang Chen <tangchen@...fujitsu.com>
Cc: mtosatti@...hat.com, nadav.amit@...il.com, jan.kiszka@....de,
kvm@...r.kernel.org, laijs@...fujitsu.com,
isimatu.yasuaki@...fujitsu.com, guz.fnst@...fujitsu.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/6] kvm, mem-hotplug: Reload L1's apic access page on
migration when L2 is running.
On Wed, Aug 27, 2014 at 06:17:40PM +0800, Tang Chen wrote:
> This patch only handle "L1 and L2 vm share one apic access page" situation.
>
> When L1 vm is running, if the shared apic access page is migrated, mmu_notifier will
> request all vcpus to exit to L0, and reload apic access page physical address for
> all the vcpus' vmcs (which is done by patch 5/6). And when it enters L2 vm, L2's vmcs
> will be updated in prepare_vmcs02() called by nested_vm_run(). So we need to do
> nothing.
>
> When L2 vm is running, if the shared apic access page is migrated, mmu_notifier will
> request all vcpus to exit to L0, and reload apic access page physical address for
> all L2 vmcs. And this patch requests apic access page reload in L2->L1 vmexit.
>
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm.c | 6 ++++++
> arch/x86/kvm/vmx.c | 32 ++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.c | 3 +++
> virt/kvm/kvm_main.c | 1 +
> 5 files changed, 43 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 514183e..13fbb62 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -740,6 +740,7 @@ struct kvm_x86_ops {
> void (*load_eoi_exitmap)(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap);
> void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
> void (*set_apic_access_page_addr)(struct kvm *kvm, hpa_t hpa);
> + void (*set_nested_apic_page_migrated)(struct kvm_vcpu *vcpu, bool set);
> void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
> void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
> int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f2eacc4..da88646 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3624,6 +3624,11 @@ static void svm_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
> return;
> }
>
> +static void svm_set_nested_apic_page_migrated(struct kvm_vcpu *vcpu, bool set)
> +{
> + return;
> +}
> +
> static int svm_vm_has_apicv(struct kvm *kvm)
> {
> return 0;
> @@ -4379,6 +4384,7 @@ static struct kvm_x86_ops svm_x86_ops = {
> .update_cr8_intercept = update_cr8_intercept,
> .set_virtual_x2apic_mode = svm_set_virtual_x2apic_mode,
> .set_apic_access_page_addr = svm_set_apic_access_page_addr,
> + .set_nested_apic_page_migrated = svm_set_nested_apic_page_migrated,
> .vm_has_apicv = svm_vm_has_apicv,
> .load_eoi_exitmap = svm_load_eoi_exitmap,
> .hwapic_isr_update = svm_hwapic_isr_update,
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index da6d55d..9035fd1 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -379,6 +379,16 @@ struct nested_vmx {
> * we must keep them pinned while L2 runs.
> */
> struct page *apic_access_page;
> + /*
> + * L1's apic access page can be migrated. When L1 and L2 are sharing
> + * the apic access page, after the page is migrated when L2 is running,
> + * we have to reload it to L1 vmcs before we enter L1.
> + *
> + * When the shared apic access page is migrated in L1 mode, we don't
> + * need to do anything else because we reload apic access page each
> + * time when entering L2 in prepare_vmcs02().
> + */
> + bool apic_access_page_migrated;
> u64 msr_ia32_feature_control;
>
> struct hrtimer preemption_timer;
> @@ -7098,6 +7108,12 @@ static void vmx_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
> vmcs_write64(APIC_ACCESS_ADDR, hpa);
> }
>
> +static void vmx_set_nested_apic_page_migrated(struct kvm_vcpu *vcpu, bool set)
> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + vmx->nested.apic_access_page_migrated = set;
> +}
> +
> static void vmx_hwapic_isr_update(struct kvm *kvm, int isr)
> {
> u16 status;
> @@ -8796,6 +8812,21 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
> }
>
> /*
> + * When shared (L1 & L2) apic access page is migrated during L2 is
> + * running, mmu_notifier will force to reload the page's hpa for L2
> + * vmcs. Need to reload it for L1 before entering L1.
> + */
> + if (vmx->nested.apic_access_page_migrated) {
> + /*
> + * Do not call kvm_reload_apic_access_page() because we are now
> + * in L2. We should not call make_all_cpus_request() to exit to
> + * L0, otherwise we will reload for L2 vmcs again.
> + */
> + kvm_reload_apic_access_page(vcpu->kvm);
> + vmx->nested.apic_access_page_migrated = false;
> + }
I would just call kvm_reload_apic_access_page() unconditionally and only if
it will prove to be performance problem would optimize it further. Vmexit emulation it
pretty heavy, so I doubt one more vmwrite will be noticeable.
--
Gleb.
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