linux-kernel - Re: [Question] int3 instruction generates a #UD in SEV VM

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Message-ID: <ZMp3sAQqRlNYqfwr@google.com>
Date:   Wed, 2 Aug 2023 08:35:12 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Wu Zongyo <wuzongyo@...l.ustc.edu.cn>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        linux-coco@...ts.linux.dev
Subject: Re: [Question] int3 instruction generates a #UD in SEV VM

On Wed, Aug 02, 2023, Tom Lendacky wrote:
> On 8/2/23 10:04, Sean Christopherson wrote:
> > Side topic, KVM should require nrips for SEV and beyond, I don't see how SEV can
> > possibly work if KVM doesn't utilize nrips.  E.g. this
> > 
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 2eace114a934..43e500503d48 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -5111,9 +5111,11 @@ static __init int svm_hardware_setup(void)
> >          svm_adjust_mmio_mask();
> > +       nrips = nrips && boot_cpu_has(X86_FEATURE_NRIPS);
> > +
> >          /*
> >           * Note, SEV setup consumes npt_enabled and enable_mmio_caching (which
> > -        * may be modified by svm_adjust_mmio_mask()).
> > +        * may be modified by svm_adjust_mmio_mask()), as well as nrips.
> >           */
> >          sev_hardware_setup();
> 
> You moved the setting of nrips up, I'm assuming you then want to add a check
> in sev_hardware_setup() for nrips?

Doh.  I like to think I would have noticed that I forgot to add that check before
postinga patch, but I give myself 50/50 odds at best.