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

[Gleb Natapov]

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@xxxxxxxxxxxxxx>
> ---
>  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.
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