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Date: Tue, 2 Sep 2014 19:00:05 +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 4/6] kvm, mem-hotplug: Reload L1' apic access page on
migration in vcpu_enter_guest().
On Wed, Aug 27, 2014 at 06:17:39PM +0800, Tang Chen wrote:
> apic access page is pinned in memory. As a result, it cannot be migrated/hot-removed.
> Actually, it is not necessary to be pinned.
>
> The hpa of apic access page is stored in VMCS APIC_ACCESS_ADDR pointer. When
> the page is migrated, kvm_mmu_notifier_invalidate_page() will invalidate the
> corresponding ept entry. This patch introduces a new vcpu request named
> KVM_REQ_APIC_PAGE_RELOAD, and makes this request to all the vcpus at this time,
> and force all the vcpus exit guest, and re-enter guest till they updates the VMCS
> APIC_ACCESS_ADDR pointer to the new apic access page address, and updates
> kvm->arch.apic_access_page to the new page.
>
> 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 | 6 ++++++
> arch/x86/kvm/x86.c | 15 +++++++++++++++
> include/linux/kvm_host.h | 2 ++
> virt/kvm/kvm_main.c | 12 ++++++++++++
> 6 files changed, 42 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 35171c7..514183e 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -739,6 +739,7 @@ struct kvm_x86_ops {
> void (*hwapic_isr_update)(struct kvm *kvm, int isr);
> 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 (*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 1d941ad..f2eacc4 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3619,6 +3619,11 @@ static void svm_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
> return;
> }
>
> +static void svm_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
> +{
> + return;
> +}
> +
> static int svm_vm_has_apicv(struct kvm *kvm)
> {
> return 0;
> @@ -4373,6 +4378,7 @@ static struct kvm_x86_ops svm_x86_ops = {
> .enable_irq_window = enable_irq_window,
> .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,
> .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 63c4c3e..da6d55d 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7093,6 +7093,11 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
> vmx_set_msr_bitmap(vcpu);
> }
>
> +static void vmx_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
> +{
> + vmcs_write64(APIC_ACCESS_ADDR, hpa);
> +}
> +
> static void vmx_hwapic_isr_update(struct kvm *kvm, int isr)
> {
> u16 status;
> @@ -8910,6 +8915,7 @@ static struct kvm_x86_ops vmx_x86_ops = {
> .enable_irq_window = enable_irq_window,
> .update_cr8_intercept = update_cr8_intercept,
> .set_virtual_x2apic_mode = vmx_set_virtual_x2apic_mode,
> + .set_apic_access_page_addr = vmx_set_apic_access_page_addr,
> .vm_has_apicv = vmx_vm_has_apicv,
> .load_eoi_exitmap = vmx_load_eoi_exitmap,
> .hwapic_irr_update = vmx_hwapic_irr_update,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e05bd58..96f4188 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5989,6 +5989,19 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
> kvm_apic_update_tmr(vcpu, tmr);
> }
>
> +static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
> +{
> + /*
> + * apic access page could be migrated. When the page is being migrated,
> + * GUP will wait till the migrate entry is replaced with the new pte
> + * entry pointing to the new page.
> + */
> + vcpu->kvm->arch.apic_access_page = gfn_to_page(vcpu->kvm,
> + APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> + kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm,
> + page_to_phys(vcpu->kvm->arch.apic_access_page));
I am a little bit worried that here all vcpus write to vcpu->kvm->arch.apic_access_page
without any locking. It is probably benign since pointer write is atomic on x86. Paolo?
Do we even need apic_access_page? Why not call
gfn_to_page(APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT)
put_page()
on rare occasions we need to know its address?
> +}
> +
> /*
> * Returns 1 to let __vcpu_run() continue the guest execution loop without
> * exiting to the userspace. Otherwise, the value will be returned to the
> @@ -6049,6 +6062,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> kvm_deliver_pmi(vcpu);
> if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
> vcpu_scan_ioapic(vcpu);
> + if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
> + vcpu_reload_apic_access_page(vcpu);
> }
>
> if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a4c33b3..8be076a 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -136,6 +136,7 @@ static inline bool is_error_page(struct page *page)
> #define KVM_REQ_GLOBAL_CLOCK_UPDATE 22
> #define KVM_REQ_ENABLE_IBS 23
> #define KVM_REQ_DISABLE_IBS 24
> +#define KVM_REQ_APIC_PAGE_RELOAD 25
>
> #define KVM_USERSPACE_IRQ_SOURCE_ID 0
> #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
> @@ -579,6 +580,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm);
> void kvm_reload_remote_mmus(struct kvm *kvm);
> void kvm_make_mclock_inprogress_request(struct kvm *kvm);
> void kvm_make_scan_ioapic_request(struct kvm *kvm);
> +void kvm_reload_apic_access_page(struct kvm *kvm);
>
> long kvm_arch_dev_ioctl(struct file *filp,
> unsigned int ioctl, unsigned long arg);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 33712fb..d8280de 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -210,6 +210,11 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm)
> make_all_cpus_request(kvm, KVM_REQ_SCAN_IOAPIC);
> }
>
> +void kvm_reload_apic_access_page(struct kvm *kvm)
> +{
> + make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD);
> +}
> +
> int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
> {
> struct page *page;
> @@ -294,6 +299,13 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
> if (need_tlb_flush)
> kvm_flush_remote_tlbs(kvm);
>
> + /*
> + * The physical address of apic access page is stroed in VMCS.
> + * So need to update it when it becomes invalid.
> + */
> + if (address == gfn_to_hva(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT))
> + kvm_reload_apic_access_page(kvm);
> +
> spin_unlock(&kvm->mmu_lock);
> srcu_read_unlock(&kvm->srcu, idx);
> }
> --
> 1.8.3.1
>
--
Gleb.
--
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