Re: [PATCH v6 07/14] KVM: x86: Add AMD SEV specific Hypercall3

[Steve Rutherford]

On Thu, Apr 2, 2020 at 4:56 PM Krish Sadhukhan
<krish.sadhukhan@xxxxxxxxxx> wrote:
>
>
> On 3/29/20 11:21 PM, Ashish Kalra wrote:
> > From: Brijesh Singh <Brijesh.Singh@xxxxxxx>
> >
> > KVM hypercall framework relies on alternative framework to patch the
> > VMCALL -> VMMCALL on AMD platform. If a hypercall is made before
> > apply_alternative()
>
> s/apply_alternative/apply_alternatives/
> > is called then it defaults to VMCALL. The approach
> > works fine on non SEV guest. A VMCALL would causes #UD, and hypervisor
> > will be able to decode the instruction and do the right things. But
> > when SEV is active, guest memory is encrypted with guest key and
> > hypervisor will not be able to decode the instruction bytes.
> >
> > Add SEV specific hypercall3, it unconditionally uses VMMCALL. The hypercall
> > will be used by the SEV guest to notify encrypted pages to the hypervisor.
> >
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxx>
> > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_para.h | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> > index 9b4df6eaa11a..6c09255633a4 100644
> > --- a/arch/x86/include/asm/kvm_para.h
> > +++ b/arch/x86/include/asm/kvm_para.h
> > @@ -84,6 +84,18 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
> >       return ret;
> >   }
> >
> > +static inline long kvm_sev_hypercall3(unsigned int nr, unsigned long p1,
> > +                                   unsigned long p2, unsigned long p3)
> > +{
> > +     long ret;
> > +
> > +     asm volatile("vmmcall"
> > +                  : "=a"(ret)
> > +                  : "a"(nr), "b"(p1), "c"(p2), "d"(p3)
> > +                  : "memory");
> > +     return ret;
> > +}
> > +
> >   #ifdef CONFIG_KVM_GUEST
> >   bool kvm_para_available(void);
> >   unsigned int kvm_arch_para_features(void);
> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>

Nit: I'd personally have named this kvm_vmmcall3, since it's about
invoking a particular instruction. The usage happens to be for SEV.

Reviewed-by: Steve Rutherford <srutherford@xxxxxxxxxx>