Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page in memory.

Gleb Natapov
2014-07-12T08:04:48Z

On Tue, Jul 08, 2014 at 09:01:32PM +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.
>
By default kvm Linux guest uses x2apic, so APIC_ACCESS_ADDR mechanism
is not used since no MMIO access to APIC is ever done. Have you tested
this with "-cpu modelname,-x2apic" qemu flag?

> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/mmu.c | 11 +++++++++++
> arch/x86/kvm/svm.c | 6 ++++++
> arch/x86/kvm/vmx.c | 8 +++++++-
> arch/x86/kvm/x86.c | 14 ++++++++++++++
> include/linux/kvm_host.h | 2 ++
> virt/kvm/kvm_main.c | 12 ++++++++++++
> 7 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 62f973e..9ce6bfd 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -737,6 +737,7 @@ 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/mmu.c b/arch/x86/kvm/mmu.c
> index 9314678..551693d 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3427,6 +3427,17 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
> level, gfn, pfn, prefault);
> spin_unlock(&vcpu->kvm->mmu_lock);
>
> + /*
> + * apic access page could be migrated. When the guest tries to access
> + * the apic access page, ept violation will occur, and we can use GUP
> + * to find the new page.
> + *
> + * GUP will wait till the migrate entry be replaced with the new page.
> + */
> + if (gpa == APIC_DEFAULT_PHYS_BASE)
> + vcpu->kvm->arch.apic_access_page = gfn_to_page_no_pin(vcpu->kvm,
> + APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
Shouldn't you make KVM_REQ_APIC_PAGE_RELOAD request here?

> +
> return r;
>
> out_unlock:
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 576b525..dc76f29 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3612,6 +3612,11 @@ 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;
> @@ -4365,6 +4370,7 @@ 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 5532ac8..f7c6313 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3992,7 +3992,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
> if (r)
> goto out;
>
> - page = gfn_to_page(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> + page = gfn_to_page_no_pin(kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> if (is_error_page(page)) {
> r = -EFAULT;
> goto out;
> @@ -7073,6 +7073,11 @@ 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;
> @@ -8842,6 +8847,7 @@ 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 ffbe557..7080eda 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5929,6 +5929,18 @@ 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)
> +{
> + /*
> + * 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.
> + */
> + struct page *page = gfn_to_page_no_pin(vcpu->kvm,
> + APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
If you do not use kvm->arch.apic_access_page to get current address why not drop it entirely?

> + kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm,
> + page_to_phys(page));
> +}
> +
> /*
> * Returns 1 to let __vcpu_run() continue the guest execution loop without
> * exiting to the userspace. Otherwise, the value will be returned to the
> @@ -5989,6 +6001,8 @@ 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 7c58d9d..f49be86 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
> @@ -596,6 +597,7 @@ 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 6091849..965b702 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);
> }

You forgot to drop put_page(kvm->arch.apic_access_page); from x86.c again.

--
Gleb.