[PATCH RESEND] KVM: X86: Fix load bad host fpu state

[PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@hotmail.com>

------------[ cut here ]------------
 Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
 WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
 CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
 RIP: 0010:ex_handler_fprestore+0x88/0x90
 Call Trace:
  fixup_exception+0x4e/0x60
  do_general_protection+0xff/0x270
  general_protection+0x22/0x30
 RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
 RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
  kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
  kvm_apic_accept_events+0x1c0/0x240 [kvm]
  kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
  kvm_vcpu_ioctl+0x479/0x880 [kvm]
  do_vfs_ioctl+0x142/0x9a0
  SyS_ioctl+0x74/0x80
  do_syscall_64+0x15f/0x600

This can be reproduced by running any testcase in kvm-unit-tests since 
the qemu userspace FPU context is not initialized, which results in the 
init path from kvm_apic_accept_events() will load/put qemu userspace 
FPU context w/o initialized. In addition, w/o this splatting we still 
should initialize vcpu->arch.user_fpu instead of current->thread.fpu. 
This patch fixes it by initializing qemu user FPU context if it is 
uninitialized before KVM_RUN.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: stable@vger.kernel.org
Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/kvm/x86.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a92b22f..063a643 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = &vcpu->arch.user_fpu;
 	int r;
 
-	fpu__initialize(fpu);
+	if (!fpu->initialized) {
+		fpstate_init(&fpu->state);
+		fpu->initialized = 1;
+	}
 
 	kvm_sigset_activate(vcpu);
 
-- 
2.7.4

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[David Hildenbrand]

On 10.12.2017 22:44, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
> ------------[ cut here ]------------
>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>  Call Trace:
>   fixup_exception+0x4e/0x60
>   do_general_protection+0xff/0x270
>   general_protection+0x22/0x30
>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>   do_vfs_ioctl+0x142/0x9a0
>   SyS_ioctl+0x74/0x80
>   do_syscall_64+0x15f/0x600
> 
> This can be reproduced by running any testcase in kvm-unit-tests since 
> the qemu userspace FPU context is not initialized, which results in the 
> init path from kvm_apic_accept_events() will load/put qemu userspace 
> FPU context w/o initialized. In addition, w/o this splatting we still 
> should initialize vcpu->arch.user_fpu instead of current->thread.fpu. 
> This patch fixes it by initializing qemu user FPU context if it is 
> uninitialized before KVM_RUN.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: stable@vger.kernel.org
> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
>  arch/x86/kvm/x86.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a92b22f..063a643 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>  
>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>  {
> -	struct fpu *fpu = &current->thread.fpu;
> +	struct fpu *fpu = &vcpu->arch.user_fpu;
>  	int r;
>  
> -	fpu__initialize(fpu);
> +	if (!fpu->initialized) {
> +		fpstate_init(&fpu->state);
> +		fpu->initialized = 1;
> +	}

Is there a chance of keeping using fpu__initialize() ? Duplicating the
code is ugly.

E.g. can't we simply initialize that in kvm_load_guest_fpu?


>  
>  	kvm_sigset_activate(vcpu);
>  
> 


-- 

Thanks,

David / dhildenb

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
> On 10.12.2017 22:44, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>
>> ------------[ cut here ]------------
>>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>  Call Trace:
>>   fixup_exception+0x4e/0x60
>>   do_general_protection+0xff/0x270
>>   general_protection+0x22/0x30
>>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>   do_vfs_ioctl+0x142/0x9a0
>>   SyS_ioctl+0x74/0x80
>>   do_syscall_64+0x15f/0x600
>>
>> This can be reproduced by running any testcase in kvm-unit-tests since
>> the qemu userspace FPU context is not initialized, which results in the
>> init path from kvm_apic_accept_events() will load/put qemu userspace
>> FPU context w/o initialized. In addition, w/o this splatting we still
>> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>> This patch fixes it by initializing qemu user FPU context if it is
>> uninitialized before KVM_RUN.
>>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Cc: Rik van Riel <riel@redhat.com>
>> Cc: stable@vger.kernel.org
>> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>> ---
>>  arch/x86/kvm/x86.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index a92b22f..063a643 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>
>>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>  {
>> -     struct fpu *fpu = &current->thread.fpu;
>> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>       int r;
>>
>> -     fpu__initialize(fpu);
>> +     if (!fpu->initialized) {
>> +             fpstate_init(&fpu->state);
>> +             fpu->initialized = 1;
>> +     }
>
> Is there a chance of keeping using fpu__initialize() ? Duplicating the
> code is ugly.

There is a warning in fpu__initialize() which results in just
current->thread.fpu can take advantage of.

>
> E.g. can't we simply initialize that in kvm_load_guest_fpu?

We still miss to initialize qemu user FPU context for the above calltrace.

Regards,
Wanpeng Li

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Peter Xu]

On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
> > On 10.12.2017 22:44, Wanpeng Li wrote:
> >> From: Wanpeng Li <wanpeng.li@hotmail.com>
> >>
> >> ------------[ cut here ]------------
> >>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
> >>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
> >>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
> >>  RIP: 0010:ex_handler_fprestore+0x88/0x90
> >>  Call Trace:
> >>   fixup_exception+0x4e/0x60
> >>   do_general_protection+0xff/0x270
> >>   general_protection+0x22/0x30
> >>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
> >>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
> >>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
> >>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
> >>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
> >>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
> >>   do_vfs_ioctl+0x142/0x9a0
> >>   SyS_ioctl+0x74/0x80
> >>   do_syscall_64+0x15f/0x600
> >>
> >> This can be reproduced by running any testcase in kvm-unit-tests since
> >> the qemu userspace FPU context is not initialized, which results in the
> >> init path from kvm_apic_accept_events() will load/put qemu userspace
> >> FPU context w/o initialized. In addition, w/o this splatting we still
> >> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
> >> This patch fixes it by initializing qemu user FPU context if it is
> >> uninitialized before KVM_RUN.
> >>
> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >> Cc: Radim Krčmář <rkrcmar@redhat.com>
> >> Cc: Rik van Riel <riel@redhat.com>
> >> Cc: stable@vger.kernel.org
> >> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> >> ---
> >>  arch/x86/kvm/x86.c | 7 +++++--
> >>  1 file changed, 5 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >> index a92b22f..063a643 100644
> >> --- a/arch/x86/kvm/x86.c
> >> +++ b/arch/x86/kvm/x86.c
> >> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
> >>
> >>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> >>  {
> >> -     struct fpu *fpu = &current->thread.fpu;
> >> +     struct fpu *fpu = &vcpu->arch.user_fpu;
> >>       int r;
> >>
> >> -     fpu__initialize(fpu);
> >> +     if (!fpu->initialized) {
> >> +             fpstate_init(&fpu->state);
> >> +             fpu->initialized = 1;
> >> +     }
> >
> > Is there a chance of keeping using fpu__initialize() ? Duplicating the
> > code is ugly.
> 
> There is a warning in fpu__initialize() which results in just
> current->thread.fpu can take advantage of.
> 
> >
> > E.g. can't we simply initialize that in kvm_load_guest_fpu?
> 
> We still miss to initialize qemu user FPU context for the above calltrace.

IMHO we should not really init the user FPU since we should always
load FPU then put FPU.  The problem now is that for vcpus that with
vcpu_id>1 we'll first put the FPU before loading it. So, instead how
about we make sure we load the FPU first even for non-bootstrap vcpus?
And we can actually drop fpu__initialize() call, like:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 064eba25c215..e6aed00ba968 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7263,13 +7263,12 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)

 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
-       struct fpu *fpu = &current->thread.fpu;
        int r;

-       fpu__initialize(fpu);
-
        kvm_sigset_activate(vcpu);

+       kvm_load_guest_fpu(vcpu);
+
        if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
                if (kvm_run->immediate_exit) {
                        r = -EINTR;
@@ -7295,14 +7294,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                }
        }

-       kvm_load_guest_fpu(vcpu);
-
        if (unlikely(vcpu->arch.complete_userspace_io)) {
                int (*cui)(struct kvm_vcpu *) = vcpu->arch.complete_userspace_io;
                vcpu->arch.complete_userspace_io = NULL;
                r = cui(vcpu);
                if (r <= 0)
-                       goto out_fpu;
+                       goto out;
        } else
                WARN_ON(vcpu->arch.pio.count || vcpu->mmio_needed);

@@ -7311,9 +7308,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
        else
                r = vcpu_run(vcpu);

-out_fpu:
-       kvm_put_guest_fpu(vcpu);
 out:
+       kvm_put_guest_fpu(vcpu);
        post_kvm_run_save(vcpu);
        kvm_sigset_deactivate(vcpu);

Thanks,

-- 
Peter Xu

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

2017-12-12 11:36 GMT+08:00 Peter Xu <peterx@redhat.com>:
> On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
>> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>> > On 10.12.2017 22:44, Wanpeng Li wrote:
>> >> From: Wanpeng Li <wanpeng.li@hotmail.com>
>> >>
>> >> ------------[ cut here ]------------
>> >>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>> >>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>> >>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>> >>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>> >>  Call Trace:
>> >>   fixup_exception+0x4e/0x60
>> >>   do_general_protection+0xff/0x270
>> >>   general_protection+0x22/0x30
>> >>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>> >>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>> >>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>> >>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>> >>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>> >>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>> >>   do_vfs_ioctl+0x142/0x9a0
>> >>   SyS_ioctl+0x74/0x80
>> >>   do_syscall_64+0x15f/0x600
>> >>
>> >> This can be reproduced by running any testcase in kvm-unit-tests since
>> >> the qemu userspace FPU context is not initialized, which results in the
>> >> init path from kvm_apic_accept_events() will load/put qemu userspace
>> >> FPU context w/o initialized. In addition, w/o this splatting we still
>> >> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>> >> This patch fixes it by initializing qemu user FPU context if it is
>> >> uninitialized before KVM_RUN.
>> >>
>> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> >> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> >> Cc: Rik van Riel <riel@redhat.com>
>> >> Cc: stable@vger.kernel.org
>> >> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>> >> ---
>> >>  arch/x86/kvm/x86.c | 7 +++++--
>> >>  1 file changed, 5 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> >> index a92b22f..063a643 100644
>> >> --- a/arch/x86/kvm/x86.c
>> >> +++ b/arch/x86/kvm/x86.c
>> >> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>> >>
>> >>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> >>  {
>> >> -     struct fpu *fpu = &current->thread.fpu;
>> >> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>> >>       int r;
>> >>
>> >> -     fpu__initialize(fpu);
>> >> +     if (!fpu->initialized) {
>> >> +             fpstate_init(&fpu->state);
>> >> +             fpu->initialized = 1;
>> >> +     }
>> >
>> > Is there a chance of keeping using fpu__initialize() ? Duplicating the
>> > code is ugly.
>>
>> There is a warning in fpu__initialize() which results in just
>> current->thread.fpu can take advantage of.
>>
>> >
>> > E.g. can't we simply initialize that in kvm_load_guest_fpu?
>>
>> We still miss to initialize qemu user FPU context for the above calltrace.
>
> IMHO we should not really init the user FPU since we should always
> load FPU then put FPU.  The problem now is that for vcpus that with
> vcpu_id>1 we'll first put the FPU before loading it. So, instead how
> about we make sure we load the FPU first even for non-bootstrap vcpus?
> And we can actually drop fpu__initialize() call, like:

It will introduce extra overhead for all the cases which can't enter
into vcpu_run(), I think move
fpstate_init(&vcpu->arch.user_fpu.state); to fx_init() is better.

Regards,
Wanpeng Li

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

2017-12-12 13:40 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2017-12-12 11:36 GMT+08:00 Peter Xu <peterx@redhat.com>:
>> On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
>>> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>>> > On 10.12.2017 22:44, Wanpeng Li wrote:
>>> >> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>> >>
>>> >> ------------[ cut here ]------------
>>> >>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>> >>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>> >>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>> >>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>> >>  Call Trace:
>>> >>   fixup_exception+0x4e/0x60
>>> >>   do_general_protection+0xff/0x270
>>> >>   general_protection+0x22/0x30
>>> >>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>> >>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>> >>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>> >>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>> >>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>> >>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>> >>   do_vfs_ioctl+0x142/0x9a0
>>> >>   SyS_ioctl+0x74/0x80
>>> >>   do_syscall_64+0x15f/0x600
>>> >>
>>> >> This can be reproduced by running any testcase in kvm-unit-tests since
>>> >> the qemu userspace FPU context is not initialized, which results in the
>>> >> init path from kvm_apic_accept_events() will load/put qemu userspace
>>> >> FPU context w/o initialized. In addition, w/o this splatting we still
>>> >> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>>> >> This patch fixes it by initializing qemu user FPU context if it is
>>> >> uninitialized before KVM_RUN.
>>> >>
>>> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> >> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> >> Cc: Rik van Riel <riel@redhat.com>
>>> >> Cc: stable@vger.kernel.org
>>> >> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>>> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>> >> ---
>>> >>  arch/x86/kvm/x86.c | 7 +++++--
>>> >>  1 file changed, 5 insertions(+), 2 deletions(-)
>>> >>
>>> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> >> index a92b22f..063a643 100644
>>> >> --- a/arch/x86/kvm/x86.c
>>> >> +++ b/arch/x86/kvm/x86.c
>>> >> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>> >>
>>> >>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>> >>  {
>>> >> -     struct fpu *fpu = &current->thread.fpu;
>>> >> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>> >>       int r;
>>> >>
>>> >> -     fpu__initialize(fpu);
>>> >> +     if (!fpu->initialized) {
>>> >> +             fpstate_init(&fpu->state);
>>> >> +             fpu->initialized = 1;
>>> >> +     }
>>> >
>>> > Is there a chance of keeping using fpu__initialize() ? Duplicating the
>>> > code is ugly.
>>>
>>> There is a warning in fpu__initialize() which results in just
>>> current->thread.fpu can take advantage of.
>>>
>>> >
>>> > E.g. can't we simply initialize that in kvm_load_guest_fpu?
>>>
>>> We still miss to initialize qemu user FPU context for the above calltrace.
>>
>> IMHO we should not really init the user FPU since we should always
>> load FPU then put FPU.  The problem now is that for vcpus that with
>> vcpu_id>1 we'll first put the FPU before loading it. So, instead how
>> about we make sure we load the FPU first even for non-bootstrap vcpus?
>> And we can actually drop fpu__initialize() call, like:
>
> It will introduce extra overhead for all the cases which can't enter
> into vcpu_run(), I think move
> fpstate_init(&vcpu->arch.user_fpu.state); to fx_init() is better.

Paolo, which method you prefer?

Regards,
Wanpeng Li

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Paolo Bonzini]

On 12/12/2017 06:40, Wanpeng Li wrote:
> 2017-12-12 11:36 GMT+08:00 Peter Xu <peterx@redhat.com>:
>> On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
>>> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>>>> On 10.12.2017 22:44, Wanpeng Li wrote:
>>>>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>>
>>>>> ------------[ cut here ]------------
>>>>>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>>>>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>>>>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>>>>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>>>>  Call Trace:
>>>>>   fixup_exception+0x4e/0x60
>>>>>   do_general_protection+0xff/0x270
>>>>>   general_protection+0x22/0x30
>>>>>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>>>>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>>>>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>>>>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>>>>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>>>>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>>>>   do_vfs_ioctl+0x142/0x9a0
>>>>>   SyS_ioctl+0x74/0x80
>>>>>   do_syscall_64+0x15f/0x600
>>>>>
>>>>> This can be reproduced by running any testcase in kvm-unit-tests since
>>>>> the qemu userspace FPU context is not initialized, which results in the
>>>>> init path from kvm_apic_accept_events() will load/put qemu userspace
>>>>> FPU context w/o initialized. In addition, w/o this splatting we still
>>>>> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>>>>> This patch fixes it by initializing qemu user FPU context if it is
>>>>> uninitialized before KVM_RUN.
>>>>>
>>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>>>> Cc: Rik van Riel <riel@redhat.com>
>>>>> Cc: stable@vger.kernel.org
>>>>> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>>>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>> ---
>>>>>  arch/x86/kvm/x86.c | 7 +++++--
>>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>>> index a92b22f..063a643 100644
>>>>> --- a/arch/x86/kvm/x86.c
>>>>> +++ b/arch/x86/kvm/x86.c
>>>>> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>>>>
>>>>>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>>>  {
>>>>> -     struct fpu *fpu = &current->thread.fpu;
>>>>> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>>>>       int r;
>>>>>
>>>>> -     fpu__initialize(fpu);
>>>>> +     if (!fpu->initialized) {
>>>>> +             fpstate_init(&fpu->state);
>>>>> +             fpu->initialized = 1;
>>>>> +     }
>>>>
>>>> Is there a chance of keeping using fpu__initialize() ? Duplicating the
>>>> code is ugly.
>>>
>>> There is a warning in fpu__initialize() which results in just
>>> current->thread.fpu can take advantage of.
>>>
>>>>
>>>> E.g. can't we simply initialize that in kvm_load_guest_fpu?
>>>
>>> We still miss to initialize qemu user FPU context for the above calltrace.
>>
>> IMHO we should not really init the user FPU since we should always
>> load FPU then put FPU.  The problem now is that for vcpus that with
>> vcpu_id>1 we'll first put the FPU before loading it. So, instead how
>> about we make sure we load the FPU first even for non-bootstrap vcpus?
>> And we can actually drop fpu__initialize() call, like:
> 
> It will introduce extra overhead for all the cases which can't enter
> into vcpu_run(), I think move
> fpstate_init(&vcpu->arch.user_fpu.state); to fx_init() is better.

Those cases with a sleeping AP are so rare that they don't matter.  They
will occur only a few times per boot.  Peter's solution is right, I've
queued it.

Thanks to both!

Paolo

Paolo

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

2017-12-13 0:16 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
> On 12/12/2017 06:40, Wanpeng Li wrote:
>> 2017-12-12 11:36 GMT+08:00 Peter Xu <peterx@redhat.com>:
>>> On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
>>>> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>>>>> On 10.12.2017 22:44, Wanpeng Li wrote:
>>>>>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>>>
>>>>>> ------------[ cut here ]------------
>>>>>>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>>>>>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>>>>>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>>>>>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>>>>>  Call Trace:
>>>>>>   fixup_exception+0x4e/0x60
>>>>>>   do_general_protection+0xff/0x270
>>>>>>   general_protection+0x22/0x30
>>>>>>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>>>>>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>>>>>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>>>>>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>>>>>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>>>>>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>>>>>   do_vfs_ioctl+0x142/0x9a0
>>>>>>   SyS_ioctl+0x74/0x80
>>>>>>   do_syscall_64+0x15f/0x600
>>>>>>
>>>>>> This can be reproduced by running any testcase in kvm-unit-tests since
>>>>>> the qemu userspace FPU context is not initialized, which results in the
>>>>>> init path from kvm_apic_accept_events() will load/put qemu userspace
>>>>>> FPU context w/o initialized. In addition, w/o this splatting we still
>>>>>> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>>>>>> This patch fixes it by initializing qemu user FPU context if it is
>>>>>> uninitialized before KVM_RUN.
>>>>>>
>>>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>>>>> Cc: Rik van Riel <riel@redhat.com>
>>>>>> Cc: stable@vger.kernel.org
>>>>>> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>>>>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>>> ---
>>>>>>  arch/x86/kvm/x86.c | 7 +++++--
>>>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>>>> index a92b22f..063a643 100644
>>>>>> --- a/arch/x86/kvm/x86.c
>>>>>> +++ b/arch/x86/kvm/x86.c
>>>>>> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>>>>>
>>>>>>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>>>>  {
>>>>>> -     struct fpu *fpu = &current->thread.fpu;
>>>>>> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>>>>>       int r;
>>>>>>
>>>>>> -     fpu__initialize(fpu);
>>>>>> +     if (!fpu->initialized) {
>>>>>> +             fpstate_init(&fpu->state);
>>>>>> +             fpu->initialized = 1;
>>>>>> +     }
>>>>>
>>>>> Is there a chance of keeping using fpu__initialize() ? Duplicating the
>>>>> code is ugly.
>>>>
>>>> There is a warning in fpu__initialize() which results in just
>>>> current->thread.fpu can take advantage of.
>>>>
>>>>>
>>>>> E.g. can't we simply initialize that in kvm_load_guest_fpu?
>>>>
>>>> We still miss to initialize qemu user FPU context for the above calltrace.
>>>
>>> IMHO we should not really init the user FPU since we should always
>>> load FPU then put FPU.  The problem now is that for vcpus that with
>>> vcpu_id>1 we'll first put the FPU before loading it. So, instead how
>>> about we make sure we load the FPU first even for non-bootstrap vcpus?
>>> And we can actually drop fpu__initialize() call, like:
>>
>> It will introduce extra overhead for all the cases which can't enter
>> into vcpu_run(), I think move
>> fpstate_init(&vcpu->arch.user_fpu.state); to fx_init() is better.
>
> Those cases with a sleeping AP are so rare that they don't matter.  They
> will occur only a few times per boot.  Peter's solution is right, I've
> queued it.

I add a trace_printk here to test Peter's solution:

        if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
                if (kvm_run->immediate_exit) {
                        r = -EINTR;
                        goto out;
                }
                kvm_vcpu_block(vcpu);
                kvm_apic_accept_events(vcpu);
                kvm_clear_request(KVM_REQ_UNHALT, vcpu);
                r = -EAGAIN;
                if (signal_pending(current)) {
                        r = -EINTR;
                        vcpu->run->exit_reason = KVM_EXIT_INTR;
                        ++vcpu->stat.signal_exits;
                }
                trace_printk("load/put make no sense\n");
                goto out;
        }

I can observe 92339 times "load/put make no sense" in the log during a
32 vCPUs guest booting on a 32 pCPUs Xeon Skylake server. The print
frequency is as below:

           <...>-207694 [016] .... 1021785.120346:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207704 [031] .... 1021785.120347:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207710 [005] .... 1021785.120349:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207687 [002] .... 1021785.120351:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207709 [018] .... 1021785.120353:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207687 [002] .... 1021785.120354:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207692 [004] .... 1021785.120354:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207698 [015] .... 1021785.120358:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207702 [029] .... 1021785.120358:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207715 [026] .... 1021785.120361:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207707 [013] .... 1021785.120362:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207712 [022] .... 1021785.120365:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207711 [006] .... 1021785.120365:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207695 [000] .... 1021785.120367:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207689 [027] .... 1021785.120367:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207703 [011] .... 1021785.120368:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207708 [007] .... 1021785.120370:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207692 [004] .... 1021785.120371:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207708 [007] .... 1021785.120372:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207708 [007] .... 1021785.120373:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207698 [015] .... 1021785.120374:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207713 [012] .... 1021785.120375:
kvm_arch_vcpu_ioctl_run: load/put make no sense
           <...>-207690 [028] .... 1021785.120376:
kvm_arch_vcpu_ioctl_run: load/put make no sense

I will send out the fx_init() solution, you can pick it if it makes sense. :)

Regards,
Wanpeng Li

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[David Hildenbrand]

On 11.12.2017 22:51, Wanpeng Li wrote:
> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>> On 10.12.2017 22:44, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>>
>>> ------------[ cut here ]------------
>>>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>>  Call Trace:
>>>   fixup_exception+0x4e/0x60
>>>   do_general_protection+0xff/0x270
>>>   general_protection+0x22/0x30
>>>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>>   do_vfs_ioctl+0x142/0x9a0
>>>   SyS_ioctl+0x74/0x80
>>>   do_syscall_64+0x15f/0x600
>>>
>>> This can be reproduced by running any testcase in kvm-unit-tests since
>>> the qemu userspace FPU context is not initialized, which results in the
>>> init path from kvm_apic_accept_events() will load/put qemu userspace
>>> FPU context w/o initialized. In addition, w/o this splatting we still
>>> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>>> This patch fixes it by initializing qemu user FPU context if it is
>>> uninitialized before KVM_RUN.
>>>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> Cc: Rik van Riel <riel@redhat.com>
>>> Cc: stable@vger.kernel.org
>>> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>> ---
>>>  arch/x86/kvm/x86.c | 7 +++++--
>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index a92b22f..063a643 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>>
>>>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>  {
>>> -     struct fpu *fpu = &current->thread.fpu;
>>> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>>       int r;
>>>
>>> -     fpu__initialize(fpu);
>>> +     if (!fpu->initialized) {
>>> +             fpstate_init(&fpu->state);
>>> +             fpu->initialized = 1;
>>> +     }
>>
>> Is there a chance of keeping using fpu__initialize() ? Duplicating the
>> code is ugly.
> 
> There is a warning in fpu__initialize() which results in just
> current->thread.fpu can take advantage of.

Wonder if it would make more sense to

a) drop the WARN
b) introduce a new variant without the WARN (the existing one can call this)

Manual initialization looks ugly.

> 
>>
>> E.g. can't we simply initialize that in kvm_load_guest_fpu?
> 
> We still miss to initialize qemu user FPU context for the above calltrace.

As load will happen before store we should be fine. But I guess it will
result in the same problem.

> 
> Regards,
> Wanpeng Li
> 


-- 

Thanks,

David / dhildenb

Re: [PATCH RESEND] KVM: X86: Fix load bad host fpu state

[Wanpeng Li]

2017-12-12 17:40 GMT+08:00 David Hildenbrand <david@redhat.com>:
> On 11.12.2017 22:51, Wanpeng Li wrote:
>> 2017-12-12 4:48 GMT+08:00 David Hildenbrand <david@redhat.com>:
>>> On 10.12.2017 22:44, Wanpeng Li wrote:
>>>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>
>>>> ------------[ cut here ]------------
>>>>  Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
>>>>  WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
>>>>  CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
>>>>  RIP: 0010:ex_handler_fprestore+0x88/0x90
>>>>  Call Trace:
>>>>   fixup_exception+0x4e/0x60
>>>>   do_general_protection+0xff/0x270
>>>>   general_protection+0x22/0x30
>>>>  RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
>>>>  RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
>>>>   kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
>>>>   kvm_apic_accept_events+0x1c0/0x240 [kvm]
>>>>   kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
>>>>   kvm_vcpu_ioctl+0x479/0x880 [kvm]
>>>>   do_vfs_ioctl+0x142/0x9a0
>>>>   SyS_ioctl+0x74/0x80
>>>>   do_syscall_64+0x15f/0x600
>>>>
>>>> This can be reproduced by running any testcase in kvm-unit-tests since
>>>> the qemu userspace FPU context is not initialized, which results in the
>>>> init path from kvm_apic_accept_events() will load/put qemu userspace
>>>> FPU context w/o initialized. In addition, w/o this splatting we still
>>>> should initialize vcpu->arch.user_fpu instead of current->thread.fpu.
>>>> This patch fixes it by initializing qemu user FPU context if it is
>>>> uninitialized before KVM_RUN.
>>>>
>>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>>> Cc: Rik van Riel <riel@redhat.com>
>>>> Cc: stable@vger.kernel.org
>>>> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
>>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>>> ---
>>>>  arch/x86/kvm/x86.c | 7 +++++--
>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index a92b22f..063a643 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -7273,10 +7273,13 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
>>>>
>>>>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>>  {
>>>> -     struct fpu *fpu = &current->thread.fpu;
>>>> +     struct fpu *fpu = &vcpu->arch.user_fpu;
>>>>       int r;
>>>>
>>>> -     fpu__initialize(fpu);
>>>> +     if (!fpu->initialized) {
>>>> +             fpstate_init(&fpu->state);
>>>> +             fpu->initialized = 1;
>>>> +     }
>>>
>>> Is there a chance of keeping using fpu__initialize() ? Duplicating the
>>> code is ugly.
>>
>> There is a warning in fpu__initialize() which results in just
>> current->thread.fpu can take advantage of.
>
> Wonder if it would make more sense to
>
> a) drop the WARN
> b) introduce a new variant without the WARN (the existing one can call this)
>
> Manual initialization looks ugly.

How about this? https://lkml.org/lkml/2017/12/12/5

Regards,
Wanpeng Li