Re: [PATCH v2 5/5] kvm, mem-hotplug: Do not pin apic access page in memory.
From: Tang Chen
Date: Mon Jul 14 2014 - 03:56:22 EST
Hi Gleb,
Thanks for the reply. Please see below.
On 07/12/2014 04:04 PM, Gleb Natapov wrote:
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?
I used the following commandline to test the patches.
# /usr/libexec/qemu-kvm -m 512M -hda /home/tangchen/xxx.img -enable-kvm
-smp 2
And I think the guest used APIC_ACCESS_ADDR mechanism because the previous
patch-set has some problem which will happen when the apic page is accessed.
And it did happen.
I'll test this patch-set with "-cpu modelname,-x2apic" 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?
I don't think we need to make KVM_REQ_APIC_PAGE_RELOAD request here.
In kvm_mmu_notifier_invalidate_page() I made the request. And the
handler called
gfn_to_page_no_pin() to get the new page, which will wait till the
migration
finished. And then updated the VMCS APIC_ACCESS_ADDR pointer. So, when
the vcpus
were forced to exit the guest mode, they would wait till the VMCS
APIC_ACCESS_ADDR
pointer was updated.
As a result, we don't need to make the 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?
I should also update kvm->arch.apic_access_page here. It is used in
other places
in kvm, so I don't think we should drop it. Will update the patch.
+ 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.
Yes...will update the patch.
Thanks.
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