Re: [PATCH] x86/kvm: move kvm_load/put_guest_xcr0 into atomic context

[Wanpeng Li]

On Fri, 12 Apr 2019 at 16:09, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 12/04/19 09:55, WANG Chao wrote:
> > guest xcr0 could leak into host when MCE happens in guest mode. Because
> > do_machine_check() could schedule out at a few places.
> >
> > For example:
> >
> > kvm_load_guest_xcr0
> > ...
> > kvm_x86_ops->run(vcpu) {
> >   vmx_vcpu_run
> >     vmx_complete_atomic_exit
> >       kvm_machine_check
> >         do_machine_check
> >           do_memory_failure
> >             memory_failure
> >               lock_page

Maybe this should not be counted to guest time in guest_exit_irqoff()?

Regards,
Wanpeng Li

> >
> > In this case, host_xcr0 is 0x2ff, guest vcpu xcr0 is 0xff. After schedule
> > out, host cpu has guest xcr0 loaded (0xff).
> >
> > In __switch_to {
> >      switch_fpu_finish
> >        copy_kernel_to_fpregs
> >          XRSTORS
> >
> > If any bit i in XSTATE_BV[i] == 1 and xcr0[i] == 0, XRSTORS will
> > generate #GP (In this case, bit 9). Then ex_handler_fprestore kicks in
> > and tries to reinitialize fpu by restoring init fpu state. Same story as
> > last #GP, except we get DOUBLE FAULT this time.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: WANG Chao <chao.wang@xxxxxxxxx>
>
> Thanks for the detailed commit message.  Patch queued!.
>
> Paolo
>
> > ---
> >  arch/x86/kvm/svm.c     |  2 ++
> >  arch/x86/kvm/vmx/vmx.c |  4 ++++
> >  arch/x86/kvm/x86.c     | 10 ++++------
> >  arch/x86/kvm/x86.h     |  2 ++
> >  4 files changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index e0a791c3d4fc..2bf73076de7f 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -5621,6 +5621,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
> >       svm->vmcb->save.cr2 = vcpu->arch.cr2;
> >
> >       clgi();
> > +     kvm_load_guest_xcr0(vcpu);
> >
> >       /*
> >        * If this vCPU has touched SPEC_CTRL, restore the guest's value if
> > @@ -5766,6 +5767,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
> >       if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
> >               kvm_before_interrupt(&svm->vcpu);
> >
> > +     kvm_put_guest_xcr0(vcpu);
> >       stgi();
> >
> >       /* Any pending NMI will happen here */
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index ab432a930ae8..3157598c52f1 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6410,6 +6410,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >       if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
> >               vmx_set_interrupt_shadow(vcpu, 0);
> >
> > +     kvm_load_guest_xcr0(vcpu);
> > +
> >       if (static_cpu_has(X86_FEATURE_PKU) &&
> >           kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
> >           vcpu->arch.pkru != vmx->host_pkru)
> > @@ -6506,6 +6508,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >                       __write_pkru(vmx->host_pkru);
> >       }
> >
> > +     kvm_put_guest_xcr0(vcpu);
> > +
> >       vmx->nested.nested_run_pending = 0;
> >       vmx->idt_vectoring_info = 0;
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 099b851dabaf..22f66e9a7dc5 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -800,7 +800,7 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_lmsw);
> >
> > -static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
> > +void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
> >  {
> >       if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
> >                       !vcpu->guest_xcr0_loaded) {
> > @@ -810,8 +810,9 @@ static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
> >               vcpu->guest_xcr0_loaded = 1;
> >       }
> >  }
> > +EXPORT_SYMBOL_GPL(kvm_load_guest_xcr0);
> >
> > -static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
> > +void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
> >  {
> >       if (vcpu->guest_xcr0_loaded) {
> >               if (vcpu->arch.xcr0 != host_xcr0)
> > @@ -819,6 +820,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
> >               vcpu->guest_xcr0_loaded = 0;
> >       }
> >  }
> > +EXPORT_SYMBOL_GPL(kvm_put_guest_xcr0);
> >
> >  static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
> >  {
> > @@ -7865,8 +7867,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >               goto cancel_injection;
> >       }
> >
> > -     kvm_load_guest_xcr0(vcpu);
> > -
> >       if (req_immediate_exit) {
> >               kvm_make_request(KVM_REQ_EVENT, vcpu);
> >               kvm_x86_ops->request_immediate_exit(vcpu);
> > @@ -7919,8 +7919,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> >       vcpu->mode = OUTSIDE_GUEST_MODE;
> >       smp_wmb();
> >
> > -     kvm_put_guest_xcr0(vcpu);
> > -
> >       kvm_before_interrupt(vcpu);
> >       kvm_x86_ops->handle_external_intr(vcpu);
> >       kvm_after_interrupt(vcpu);
> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > index 28406aa1136d..aedc5d0d4989 100644
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -347,4 +347,6 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
> >       __this_cpu_write(current_vcpu, NULL);
> >  }
> >
> > +void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu);
> > +void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu);
> >  #endif
> >
>