Re: [PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

Re: [PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

[Paolo Bonzini]

On 10/10/2017 17:39, peng.hao2@zte.com.cn wrote:
>>How did you know that this was a kvm_run page, and why is it the right
>>thing to clear the flags?
> 
> first  I can't repeat this "bad page report". But I add print message to
> trace. I found that  kvm_run page is freed  with page flags
> PG_dirty and PG_referenced. I  don't think it is right status for
> freed page.

That would be the symptom, not the cause.  So it would not be the right
thing to clear the flags.

> second, kvm_run page is mmaped in qemu with fd of "kvm-vcpu". It has
> special mmap function(kvm_vcpu_mmap),but when munmap is called 
> the kvm_run page goes into general munmap route.it is not suitable for
> kvm_run page that is set dirty in munmap route.

There are many many cases where .mmap and .fault are defined but .munmap
isn't, and none of them calls ClearPageDirty or ClearPageReferenced; see
for example kernel/relay.c (whose only user is blktrace).

Can the page be dirty in those cases?  If not, what makes KVM different?

Since you cannot reproduce the failure, this patch is basically
untested.  You need to dig deeper into what's happening, and provide a
better justification for what you are doing.  But generally, it's a bad
sign if you're doing something special that no other device in the
kernel is doing.

Paolo

Re: [PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

[Wanpeng Li]

Cc mm community.
2017-10-11 3:26 GMT+08:00 Peng Hao <peng.hao2@zte.com.cn>:
> When freeing mmapped kvm_run several pages, the pages will have page
> flags PG_dirty and PG_referenced. It will result to bad page report
> when allocating pages.
> I just encounter once like this;
> BUG: Bad page state in process qemu-system-x86  pfn:81fc5d
> page:ffffea00207f1740 count:0 mapcount:0 mapping:          (null) index:0x4
> flags: 0x600000000000014(referenced|dirty)
> raw: 0600000000000014 0000000000000000 0000000000000004 00000000ffffffff
> raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
> page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
> bad because of flags: 0x14(referenced|dirty)
> Modules linked in: kvm_intel kvm vhost_net vhost tap xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat xt_conntrack ipt_REJECT xt_tcpudp ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter openvswitch nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 mei_me crypto_simd input_leds cryptd led_class joydev shpchp mei wmi lpc_ich glue_helper mfd_core acpi_power_meter acpi_pad irqbypass ip_tables x_tables megaraid_sas [last unloaded: kvm_intel]
> CPU: 7 PID: 37349 Comm: qemu-system-x86 Tainted: G        W       4.13.0-rc6nfv+ #1
> Hardware name: Dell Inc. PowerEdge R720/068CDY, BIOS 2.2.2 01/16/2014
> Call Trace:
> dump_stack+0x63/0x8c
> bad_page+0xfe/0x11a
> check_new_page_bad+0x76/0x78
> get_page_from_freelist+0x65e/0xa00
> __alloc_pages_nodemask+0xf6/0x270
> alloc_pages_vma+0x6b/0x110
> __handle_mm_fault+0x4e2/0xb20
> handle_mm_fault+0xd8/0x1f0
> __do_page_fault+0x215/0x4b0
> do_page_fault+0x32/0x90
> page_fault+0x28/0x30
> RIP: 0033:0x7f68ca7d94fc
> RSP: 002b:00007ffe911a3570 EFLAGS: 00010216
> RAX: 00005599e0240a30 RBX: 00005599e023e920 RCX: 0000000000006c41
> RDX: 00007f68cab157b8 RSI: 0000000061d00000 RDI: 0000000000000003
> RBP: 00007f68cab15760 R08: 0000000000020000 R09: 0000000000002100
> R10: 000000000000006b R11: 0000000000000000 R12: 0000000000004b30
> R13: 0000000000006c40 R14: 0000000000002110 R15: 00007f68cab157b8
>
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> ---
>  arch/x86/kvm/x86.c        | 5 ++++-
>  virt/kvm/coalesced_mmio.c | 8 ++++++--
>  virt/kvm/kvm_main.c       | 5 ++++-
>  3 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cd17b7d..82e5ac1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8058,6 +8058,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>  void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
>  {
>         int idx;
> +       struct page *page = virt_to_page(vcpu->arch.pio_data);
>
>         kvm_hv_vcpu_uninit(vcpu);
>         kvm_pmu_destroy(vcpu);
> @@ -8066,7 +8067,9 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
>         idx = srcu_read_lock(&vcpu->kvm->srcu);
>         kvm_mmu_destroy(vcpu);
>         srcu_read_unlock(&vcpu->kvm->srcu, idx);
> -       free_page((unsigned long)vcpu->arch.pio_data);
> +       ClearPageDirty(page);
> +       ClearPageReferenced(page);

These flags should be handled by core mm instead of kvm if there is a
bug in core mm.

Regards,
Wanpeng Li

> +       __free_page(page);
>         if (!lapic_in_kernel(vcpu))
>                 static_key_slow_dec(&kvm_no_apic_vcpu);
>  }
> diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
> index 571c1ce..bd834a4 100644
> --- a/virt/kvm/coalesced_mmio.c
> +++ b/virt/kvm/coalesced_mmio.c
> @@ -129,8 +129,12 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
>
>  void kvm_coalesced_mmio_free(struct kvm *kvm)
>  {
> -       if (kvm->coalesced_mmio_ring)
> -               free_page((unsigned long)kvm->coalesced_mmio_ring);
> +       if (kvm->coalesced_mmio_ring) {
> +               struct page *page = virt_to_page(kvm->coalesced_mmio_ring);
> +               ClearPageDirty(page);
> +               ClearPageReferenced(page);
> +               __free_page(page);
> +       }
>  }
>
>  int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 9deb5a2..ee65972 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -305,6 +305,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
>
>  void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
>  {
> +       struct page *page = virt_to_page(vcpu->run);
>         /*
>          * no need for rcu_read_lock as VCPU_RUN is the only place that
>          * will change the vcpu->pid pointer and on uninit all file
> @@ -312,7 +313,9 @@ void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
>          */
>         put_pid(rcu_dereference_protected(vcpu->pid, 1));
>         kvm_arch_vcpu_uninit(vcpu);
> -       free_page((unsigned long)vcpu->run);
> +       ClearPageDirty(page);
> +       ClearPageReferenced(page);
> +       __free_page(page);
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_uninit);
>
> --
> 1.8.3.1
>

Re: [PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

[Wanpeng Li]

Cc mm community.
2017-10-11 3:26 GMT+08:00 Peng Hao <peng.hao2@zte.com.cn>:
> When freeing mmapped kvm_run several pages, the pages will have page
> flags PG_dirty and PG_referenced. It will result to bad page report
> when allocating pages.
> I just encounter once like this;
> BUG: Bad page state in process qemu-system-x86  pfn:81fc5d
> page:ffffea00207f1740 count:0 mapcount:0 mapping:          (null) index:0x4
> flags: 0x600000000000014(referenced|dirty)
> raw: 0600000000000014 0000000000000000 0000000000000004 00000000ffffffff
> raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
> page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
> bad because of flags: 0x14(referenced|dirty)
> Modules linked in: kvm_intel kvm vhost_net vhost tap xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat xt_conntrack ipt_REJECT xt_tcpudp ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter openvswitch nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 mei_me crypto_simd input_leds cryptd led_class joydev shpchp mei wmi lpc_ich glue_helper mfd_core acpi_power_meter acpi_pad irqbypass ip_tables x_tables megaraid_sas [last unloaded: kvm_intel]
> CPU: 7 PID: 37349 Comm: qemu-system-x86 Tainted: G        W       4.13.0-rc6nfv+ #1
> Hardware name: Dell Inc. PowerEdge R720/068CDY, BIOS 2.2.2 01/16/2014
> Call Trace:
> dump_stack+0x63/0x8c
> bad_page+0xfe/0x11a
> check_new_page_bad+0x76/0x78
> get_page_from_freelist+0x65e/0xa00
> __alloc_pages_nodemask+0xf6/0x270
> alloc_pages_vma+0x6b/0x110
> __handle_mm_fault+0x4e2/0xb20
> handle_mm_fault+0xd8/0x1f0
> __do_page_fault+0x215/0x4b0
> do_page_fault+0x32/0x90
> page_fault+0x28/0x30
> RIP: 0033:0x7f68ca7d94fc
> RSP: 002b:00007ffe911a3570 EFLAGS: 00010216
> RAX: 00005599e0240a30 RBX: 00005599e023e920 RCX: 0000000000006c41
> RDX: 00007f68cab157b8 RSI: 0000000061d00000 RDI: 0000000000000003
> RBP: 00007f68cab15760 R08: 0000000000020000 R09: 0000000000002100
> R10: 000000000000006b R11: 0000000000000000 R12: 0000000000004b30
> R13: 0000000000006c40 R14: 0000000000002110 R15: 00007f68cab157b8
>
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> ---
>  arch/x86/kvm/x86.c        | 5 ++++-
>  virt/kvm/coalesced_mmio.c | 8 ++++++--
>  virt/kvm/kvm_main.c       | 5 ++++-
>  3 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cd17b7d..82e5ac1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8058,6 +8058,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
>  void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
>  {
>         int idx;
> +       struct page *page = virt_to_page(vcpu->arch.pio_data);
>
>         kvm_hv_vcpu_uninit(vcpu);
>         kvm_pmu_destroy(vcpu);
> @@ -8066,7 +8067,9 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
>         idx = srcu_read_lock(&vcpu->kvm->srcu);
>         kvm_mmu_destroy(vcpu);
>         srcu_read_unlock(&vcpu->kvm->srcu, idx);
> -       free_page((unsigned long)vcpu->arch.pio_data);
> +       ClearPageDirty(page);
> +       ClearPageReferenced(page);

These flags should be handled by core mm instead of kvm if there is a
bug in core mm.

Regards,
Wanpeng Li

> +       __free_page(page);
>         if (!lapic_in_kernel(vcpu))
>                 static_key_slow_dec(&kvm_no_apic_vcpu);
>  }
> diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
> index 571c1ce..bd834a4 100644
> --- a/virt/kvm/coalesced_mmio.c
> +++ b/virt/kvm/coalesced_mmio.c
> @@ -129,8 +129,12 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
>
>  void kvm_coalesced_mmio_free(struct kvm *kvm)
>  {
> -       if (kvm->coalesced_mmio_ring)
> -               free_page((unsigned long)kvm->coalesced_mmio_ring);
> +       if (kvm->coalesced_mmio_ring) {
> +               struct page *page = virt_to_page(kvm->coalesced_mmio_ring);
> +               ClearPageDirty(page);
> +               ClearPageReferenced(page);
> +               __free_page(page);
> +       }
>  }
>
>  int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 9deb5a2..ee65972 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -305,6 +305,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
>
>  void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
>  {
> +       struct page *page = virt_to_page(vcpu->run);
>         /*
>          * no need for rcu_read_lock as VCPU_RUN is the only place that
>          * will change the vcpu->pid pointer and on uninit all file
> @@ -312,7 +313,9 @@ void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
>          */
>         put_pid(rcu_dereference_protected(vcpu->pid, 1));
>         kvm_arch_vcpu_uninit(vcpu);
> -       free_page((unsigned long)vcpu->run);
> +       ClearPageDirty(page);
> +       ClearPageReferenced(page);
> +       __free_page(page);
>  }
>  EXPORT_SYMBOL_GPL(kvm_vcpu_uninit);
>
> --
> 1.8.3.1
>

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[PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

[Peng Hao]

When freeing mmapped kvm_run several pages, the pages will have page
flags PG_dirty and PG_referenced. It will result to bad page report
when allocating pages.
I just encounter once like this;
BUG: Bad page state in process qemu-system-x86  pfn:81fc5d
page:ffffea00207f1740 count:0 mapcount:0 mapping:          (null) index:0x4
flags: 0x600000000000014(referenced|dirty)
raw: 0600000000000014 0000000000000000 0000000000000004 00000000ffffffff
raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
bad because of flags: 0x14(referenced|dirty)
Modules linked in: kvm_intel kvm vhost_net vhost tap xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat xt_conntrack ipt_REJECT xt_tcpudp ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter openvswitch nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 mei_me crypto_simd input_leds cryptd led_class joydev shpchp mei wmi lpc_ich glue_helper mfd_core acpi_power_meter acpi_pad irqbypass ip_tables x_tables megaraid_sas [last unloaded: kvm_intel]
CPU: 7 PID: 37349 Comm: qemu-system-x86 Tainted: G        W       4.13.0-rc6nfv+ #1
Hardware name: Dell Inc. PowerEdge R720/068CDY, BIOS 2.2.2 01/16/2014
Call Trace:
dump_stack+0x63/0x8c
bad_page+0xfe/0x11a
check_new_page_bad+0x76/0x78
get_page_from_freelist+0x65e/0xa00
__alloc_pages_nodemask+0xf6/0x270
alloc_pages_vma+0x6b/0x110
__handle_mm_fault+0x4e2/0xb20
handle_mm_fault+0xd8/0x1f0
__do_page_fault+0x215/0x4b0
do_page_fault+0x32/0x90
page_fault+0x28/0x30
RIP: 0033:0x7f68ca7d94fc
RSP: 002b:00007ffe911a3570 EFLAGS: 00010216
RAX: 00005599e0240a30 RBX: 00005599e023e920 RCX: 0000000000006c41
RDX: 00007f68cab157b8 RSI: 0000000061d00000 RDI: 0000000000000003
RBP: 00007f68cab15760 R08: 0000000000020000 R09: 0000000000002100
R10: 000000000000006b R11: 0000000000000000 R12: 0000000000004b30
R13: 0000000000006c40 R14: 0000000000002110 R15: 00007f68cab157b8

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
 arch/x86/kvm/x86.c        | 5 ++++-
 virt/kvm/coalesced_mmio.c | 8 ++++++--
 virt/kvm/kvm_main.c       | 5 ++++-
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd17b7d..82e5ac1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8058,6 +8058,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
 {
 	int idx;
+	struct page *page = virt_to_page(vcpu->arch.pio_data);
 
 	kvm_hv_vcpu_uninit(vcpu);
 	kvm_pmu_destroy(vcpu);
@@ -8066,7 +8067,9 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
 	idx = srcu_read_lock(&vcpu->kvm->srcu);
 	kvm_mmu_destroy(vcpu);
 	srcu_read_unlock(&vcpu->kvm->srcu, idx);
-	free_page((unsigned long)vcpu->arch.pio_data);
+	ClearPageDirty(page);
+	ClearPageReferenced(page);
+	__free_page(page);
 	if (!lapic_in_kernel(vcpu))
 		static_key_slow_dec(&kvm_no_apic_vcpu);
 }
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index 571c1ce..bd834a4 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -129,8 +129,12 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
 
 void kvm_coalesced_mmio_free(struct kvm *kvm)
 {
-	if (kvm->coalesced_mmio_ring)
-		free_page((unsigned long)kvm->coalesced_mmio_ring);
+	if (kvm->coalesced_mmio_ring) {
+		struct page *page = virt_to_page(kvm->coalesced_mmio_ring);
+		ClearPageDirty(page);
+		ClearPageReferenced(page);
+		__free_page(page);
+	}
 }
 
 int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9deb5a2..ee65972 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -305,6 +305,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 
 void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
 {
+	struct page *page = virt_to_page(vcpu->run);
 	/*
 	 * no need for rcu_read_lock as VCPU_RUN is the only place that
 	 * will change the vcpu->pid pointer and on uninit all file
@@ -312,7 +313,9 @@ void kvm_vcpu_uninit(struct kvm_vcpu *vcpu)
 	 */
 	put_pid(rcu_dereference_protected(vcpu->pid, 1));
 	kvm_arch_vcpu_uninit(vcpu);
-	free_page((unsigned long)vcpu->run);
+	ClearPageDirty(page);
+	ClearPageReferenced(page);
+	__free_page(page);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_uninit);
 
-- 
1.8.3.1

Re: [PATCH] KVM: X86: clear page flags when freeing kvm mmapping page

[Paolo Bonzini]

On 10/10/2017 21:26, Peng Hao wrote:
> When freeing mmapped kvm_run several pages, the pages will have page
> flags PG_dirty and PG_referenced. It will result to bad page report
> when allocating pages.
> I just encounter once like this;
> BUG: Bad page state in process qemu-system-x86  pfn:81fc5d
> page:ffffea00207f1740 count:0 mapcount:0 mapping:          (null) index:0x4
> flags: 0x600000000000014(referenced|dirty)
> raw: 0600000000000014 0000000000000000 0000000000000004 00000000ffffffff
> raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
> page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
> bad because of flags: 0x14(referenced|dirty)
> Modules linked in: kvm_intel kvm vhost_net vhost tap xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat xt_conntrack ipt_REJECT xt_tcpudp ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter openvswitch nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 mei_me crypto_simd input_leds cryptd led_class joydev shpchp mei wmi lpc_ich glue_helper mfd_core acpi_power_meter acpi_pad irqbypass ip_tables x_tables megaraid_sas [last unloaded: kvm_intel]
> CPU: 7 PID: 37349 Comm: qemu-system-x86 Tainted: G        W       4.13.0-rc6nfv+ #1
> Hardware name: Dell Inc. PowerEdge R720/068CDY, BIOS 2.2.2 01/16/2014
> Call Trace:
> dump_stack+0x63/0x8c
> bad_page+0xfe/0x11a
> check_new_page_bad+0x76/0x78
> get_page_from_freelist+0x65e/0xa00
> __alloc_pages_nodemask+0xf6/0x270
> alloc_pages_vma+0x6b/0x110
> __handle_mm_fault+0x4e2/0xb20
> handle_mm_fault+0xd8/0x1f0
> __do_page_fault+0x215/0x4b0
> do_page_fault+0x32/0x90
> page_fault+0x28/0x30
> RIP: 0033:0x7f68ca7d94fc
> RSP: 002b:00007ffe911a3570 EFLAGS: 00010216
> RAX: 00005599e0240a30 RBX: 00005599e023e920 RCX: 0000000000006c41
> RDX: 00007f68cab157b8 RSI: 0000000061d00000 RDI: 0000000000000003
> RBP: 00007f68cab15760 R08: 0000000000020000 R09: 0000000000002100
> R10: 000000000000006b R11: 0000000000000000 R12: 0000000000004b30
> R13: 0000000000006c40 R14: 0000000000002110 R15: 00007f68cab157b8

How did you know that this was a kvm_run page, and why is it the right
thing to clear the flags?

Paolo