2021-05-03 18:05:57

by Maxim Levitsky

Subject: [PATCH 5/5] KVM: nSVM: set a dummy exit reason in L1 vmcb when loading the nested state

Since the nested migration is a result of a VMRUN, this makes it
possible to keep a warning that L1 vmcb should always have
VMRUN exit reason when switching back to it, which
otherwise triggers incorrectly.

Signed-off-by: Maxim Levitsky <[email protected]>
---
arch/x86/kvm/svm/nested.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 12a12ae940fa..146be4b5084b 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1338,6 +1338,12 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
svm->vmcb01.ptr->save.rip = save->rip;
svm->vmcb01.ptr->save.cpl = 0;

+ /*
+ * For consistency sake, restore the L1 exit reason
+ * (that happened prior to the migration) to SVM_EXIT_VMRUN.
+ */
+ svm->vmcb->control.exit_code = SVM_EXIT_VMRUN;
+
nested_load_control_from_vmcb12(svm, ctl);

svm_switch_vmcb(svm, &svm->nested.vmcb02);
--
2.26.2

2021-05-03 18:08:49

by Maxim Levitsky

Subject: Re: [PATCH 5/5] KVM: nSVM: set a dummy exit reason in L1 vmcb when loading the nested state

On Mon, 2021-05-03 at 16:02 +0200, Paolo Bonzini wrote:
> On 03/05/21 14:54, Maxim Levitsky wrote:
> > Since the nested migration is a result of a VMRUN, this makes it
> > possible to keep a warning that L1 vmcb should always have
> > VMRUN exit reason when switching back to it, which
> > otherwise triggers incorrectly.
> >
> > Signed-off-by: Maxim Levitsky <[email protected]>
>
> Does this fix "KVM: nSVM: If VMRUN is single-stepped, queue the #DB
> intercept in nested_svm_vmexit()"? I don't like this, and also vmcb12
> is not initialized here (nested_load_control_from_vmcb12 is using the
> state passed in from userspace instead).

>
> I think you should just remove the WARN instead.
All right, I'll do this!

Best regards,
Maxim Levitsky


>
> Paolo
>
> > ---
> > arch/x86/kvm/svm/nested.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index 12a12ae940fa..146be4b5084b 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -1338,6 +1338,12 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> > svm->vmcb01.ptr->save.rip = save->rip;
> > svm->vmcb01.ptr->save.cpl = 0;
> >
> > + /*
> > + * For consistency sake, restore the L1 exit reason
> > + * (that happened prior to the migration) to SVM_EXIT_VMRUN.
> > + */
> > + svm->vmcb->control.exit_code = SVM_EXIT_VMRUN;
> > +
> > nested_load_control_from_vmcb12(svm, ctl);
> >
> > svm_switch_vmcb(svm, &svm->nested.vmcb02);
> >

2021-05-03 18:09:20

by Paolo Bonzini

Subject: Re: [PATCH 5/5] KVM: nSVM: set a dummy exit reason in L1 vmcb when loading the nested state

On 03/05/21 14:54, Maxim Levitsky wrote:
> Since the nested migration is a result of a VMRUN, this makes it
> possible to keep a warning that L1 vmcb should always have
> VMRUN exit reason when switching back to it, which
> otherwise triggers incorrectly.
>
> Signed-off-by: Maxim Levitsky <[email protected]>

Does this fix "KVM: nSVM: If VMRUN is single-stepped, queue the #DB
intercept in nested_svm_vmexit()"? I don't like this, and also vmcb12
is not initialized here (nested_load_control_from_vmcb12 is using the
state passed in from userspace instead).

I think you should just remove the WARN instead.

Paolo

> ---
> arch/x86/kvm/svm/nested.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 12a12ae940fa..146be4b5084b 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1338,6 +1338,12 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> svm->vmcb01.ptr->save.rip = save->rip;
> svm->vmcb01.ptr->save.cpl = 0;
>
> + /*
> + * For consistency sake, restore the L1 exit reason
> + * (that happened prior to the migration) to SVM_EXIT_VMRUN.
> + */
> + svm->vmcb->control.exit_code = SVM_EXIT_VMRUN;
> +
> nested_load_control_from_vmcb12(svm, ctl);
>
> svm_switch_vmcb(svm, &svm->nested.vmcb02);
>