RE: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT interception when not allowed

[Kechen Lu]

Hi Zhao,

> -----Original Message-----
> From: Zhao Liu <zhao1.liu@xxxxxxxxxxxxxxx>
> Sent: Tuesday, January 31, 2023 4:12 AM
> To: Kechen Lu <kechenl@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; seanjc@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> zhi.wang.linux@xxxxxxxxx; chao.gao@xxxxxxxxx; shaoqin.huang@xxxxxxxxx;
> vkuznets@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT
> interception when not allowed
> 
> External email: Use caution opening links or attachments
> 
> 
> On Sat, Jan 21, 2023 at 02:07:35AM +0000, Kechen Lu wrote:
> > Date: Sat, 21 Jan 2023 02:07:35 +0000
> > From: Kechen Lu <kechenl@xxxxxxxxxx>
> > Subject: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT
> > interception when not allowed
> > X-Mailer: git-send-email 2.34.1
> >
> > From: Sean Christopherson <seanjc@xxxxxxxxxx>
> >
> > Reject KVM_CAP_X86_DISABLE_EXITS if userspace attempts to disable
> > MWAIT exits and KVM previously reported (via KVM_CHECK_EXTENSION)
> that
> > MWAIT is not allowed in guest, e.g. because it's not supported or the
> > CPU doesn't have an aways-running
> 
> nit: always-running?

Ack. Thanks.

BR,
Kechen

> 
> > APIC timer.
> >
> > Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT
> > intercepts")
> >
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Kechen Lu <kechenl@xxxxxxxxxx>
> > ---
> >  arch/x86/kvm/x86.c | 20 +++++++++++++-------
> >  1 file changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index
> > 9a77b55142c6..60caa3fd40e5 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -4326,6 +4326,16 @@ static inline bool
> kvm_can_mwait_in_guest(void)
> >               boot_cpu_has(X86_FEATURE_ARAT);  }
> >
> > +static u64 kvm_get_allowed_disable_exits(void)
> > +{
> > +     u64 r = KVM_X86_DISABLE_VALID_EXITS;
> > +
> > +     if (!kvm_can_mwait_in_guest())
> > +             r &= ~KVM_X86_DISABLE_EXITS_MWAIT;
> > +
> > +     return r;
> > +}
> > +
> >  static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
> >                                           struct kvm_cpuid2 __user
> > *cpuid_arg)  { @@ -4448,10 +4458,7 @@ int
> > kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >               r = KVM_CLOCK_VALID_FLAGS;
> >               break;
> >       case KVM_CAP_X86_DISABLE_EXITS:
> > -             r |=  KVM_X86_DISABLE_EXITS_HLT |
> KVM_X86_DISABLE_EXITS_PAUSE |
> > -                   KVM_X86_DISABLE_EXITS_CSTATE;
> > -             if(kvm_can_mwait_in_guest())
> > -                     r |= KVM_X86_DISABLE_EXITS_MWAIT;
> > +             r |= kvm_get_allowed_disable_exits();
> >               break;
> >       case KVM_CAP_X86_SMM:
> >               if (!IS_ENABLED(CONFIG_KVM_SMM)) @@ -6224,15 +6231,14 @@
> > int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> >               break;
> >       case KVM_CAP_X86_DISABLE_EXITS:
> >               r = -EINVAL;
> > -             if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
> > +             if (cap->args[0] & ~kvm_get_allowed_disable_exits())
> >                       break;
> >
> >               mutex_lock(&kvm->lock);
> >               if (kvm->created_vcpus)
> >                       goto disable_exits_unlock;
> >
> > -             if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
> > -                     kvm_can_mwait_in_guest())
> > +             if (cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT)
> >                       kvm->arch.mwait_in_guest = true;
> >               if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
> >                       kvm->arch.hlt_in_guest = true;
> > --
> > 2.34.1
> >