Re: [PATCH 4/4] kvm, mem-hotplug: Update apic access page when it is migrated.

From: Tang Chen
Date: Thu Jul 03 2014 - 22:19:03 EST

Hi Gleb,

Thanks for the advices. Please see below.

On 07/03/2014 09:55 PM, Gleb Natapov wrote:
......
@@ -575,6 +575,7 @@ struct kvm_arch {

unsigned int tss_addr;
struct page *apic_access_page;
+ bool apic_access_page_migrated;
Better have two requests KVM_REQ_APIC_PAGE_MAP, KVM_REQ_APIC_PAGE_UNMAP IMO.


vcpu->requests is an unsigned long, and we can only has 64 requests. Isn't
adding two requests for apic page and another similar two for ept page too
many ? Not sure.


gpa_t wall_clock;

@@ -739,6 +740,7 @@ 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 c0d72f6..a655444 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3436,6 +3436,21 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa, u32 error_code,
kvm_make_request(KVM_REQ_MIGRATE_EPT, vcpu);
}

+ if (gpa == VMX_APIC_ACCESS_PAGE_ADDR&&
+ vcpu->kvm->arch.apic_access_page_migrated) {
Why check arch.apic_access_page_migrated here? Isn't it enough that the fault is on apic
address.


True. It's enough. Followed.

+ int i;
+
+ vcpu->kvm->arch.apic_access_page_migrated = false;
+
+ /*
+ * We need update APIC_ACCESS_ADDR pointer in each VMCS of
+ * all the online vcpus.
+ */
+ for (i = 0; i< atomic_read(&vcpu->kvm->online_vcpus); i++)
+ kvm_make_request(KVM_REQ_MIGRATE_APIC,
+ vcpu->kvm->vcpus[i]);
make_all_cpus_request(). You need to kick all vcpus from a guest mode.


OK, followed. But would you please explain more about this. :)
Why need to kick all vcpus from guest mode when making request to all vcpus ?

+ }
+
spin_unlock(&vcpu->kvm->mmu_lock);

return r;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c336cb3..abc152f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3988,7 +3988,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
if (r)
goto out;

- page = gfn_to_page(kvm, VMX_APIC_ACCESS_PAGE_ADDR>> PAGE_SHIFT);
+ page = gfn_to_page_no_pin(kvm, VMX_APIC_ACCESS_PAGE_ADDR>> PAGE_SHIFT);
if (is_error_page(page)) {
r = -EFAULT;
goto out;
@@ -7075,6 +7075,12 @@ 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)
+{
+ if (vm_need_virtualize_apic_accesses(kvm))
This shouldn't even been called if apic access page is not supported. Nor
mmu_notifier path neither tdp_page_fault path should ever see 0xfee00000
address. BUG() is more appropriate here.


I don't quite understand. Why calling this function here will leed to bug ?
(Sorry, I'm not quite understand the internal of KVM. Please help.)


+ vmcs_write64(APIC_ACCESS_ADDR, hpa);
+}
+
static void vmx_hwapic_isr_update(struct kvm *kvm, int isr)
{
u16 status;
@@ -8846,6 +8852,7 @@ 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,
svm needs that too.


OK, will add one for svm.

.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 a26524f..14e7174 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5943,6 +5943,24 @@ static void vcpu_migrated_page_update_ept(struct kvm_vcpu *vcpu)
}
}

+static void vcpu_migrated_page_update_apic(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+
+ if (kvm->arch.apic_access_page_migrated) {
+ if (kvm->arch.apic_access_page)
+ kvm->arch.apic_access_page = pfn_to_page(0);
All vcpus will access apic_access_page without locking here. May be
set kvm->arch.apic_access_page to zero in mmu_notifier and here call
kvm_x86_ops->set_apic_access_page_addr(kvm, kvm->arch.apic_access_page);


I'm a little confused. apic access page's phys_addr is stored in vmcs, and
I think it will be used by vcpu directly to access the physical page.
Setting kvm->arch.apic_access_page to zero will not stop it, right ?

I'm wondering what happens when apic page is migrated, but the vmcs is still
holding its old phys_addr before the vcpu request is handled.


+ kvm_x86_ops->set_apic_access_page_addr(kvm, 0x0ull);
+ } else {
+ struct page *page;
+ page = gfn_to_page_no_pin(kvm,
+ VMX_APIC_ACCESS_PAGE_ADDR>> PAGE_SHIFT);
+ kvm->arch.apic_access_page = page;
Same, set it during tdp fault when page is mapped.

+ kvm_x86_ops->set_apic_access_page_addr(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
@@ -6005,6 +6023,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
vcpu_scan_ioapic(vcpu);
if (kvm_check_request(KVM_REQ_MIGRATE_EPT, vcpu))
vcpu_migrated_page_update_ept(vcpu);
+ if (kvm_check_request(KVM_REQ_MIGRATE_APIC, vcpu))
+ vcpu_migrated_page_update_apic(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 4b7e51a..e2ad65e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -137,6 +137,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_ENABLE_IBS 23
#define KVM_REQ_DISABLE_IBS 24
#define KVM_REQ_MIGRATE_EPT 25
+#define KVM_REQ_MIGRATE_APIC 26

#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d271e89..f06438c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -54,6 +54,7 @@
#include<asm/io.h>
#include<asm/uaccess.h>
#include<asm/pgtable.h>
+#include<asm/vmx.h>

#include "coalesced_mmio.h"
#include "async_pf.h"
@@ -300,6 +301,20 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
kvm_make_request(KVM_REQ_MIGRATE_EPT, kvm->vcpus[0]);
}

+ if (address ==
+ gfn_to_hva(kvm, VMX_APIC_ACCESS_PAGE_ADDR>> PAGE_SHIFT)) {
+ int i;
+
+ kvm->arch.apic_access_page_migrated = true;
+
+ /*
+ * We need update APIC_ACCESS_ADDR pointer in each VMCS of
+ * all the online vcpus.
+ */
+ for (i = 0; i< atomic_read(&kvm->online_vcpus); i++)
+ kvm_make_request(KVM_REQ_MIGRATE_APIC, kvm->vcpus[i]);
+ }
make_all_cpus_request()

Also you need to drop put_page(kvm->arch.apic_access_page); from x86.c

Yes. Forgot it.

Thanks. :)

+
spin_unlock(&kvm->mmu_lock);
srcu_read_unlock(&kvm->srcu, idx);
}
--
1.8.3.1


--
Gleb.
.

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