On Tue, Dec 01, 2020, Ashish Kalra wrote: > From: Brijesh Singh <[email protected]> > > KVM hypercall framework relies on alternative framework to patch the > VMCALL -> VMMCALL on AMD platform. If a hypercall is made before > apply_alternative() 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.
What if we invert KVM_HYPERCALL and X86_FEATURE_VMMCALL to default to VMMCALL and opt into VMCALL? It's a synthetic feature flag either way, and I don't think there are any existing KVM hypercalls that happen before alternatives are patched, i.e. it'll be a nop for sane kernel builds. I'm also skeptical that a KVM specific hypercall is the right approach for the encryption behavior, but I'll take that up in the patches later in the series. > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: "Radim Krčmář" <[email protected]> > Cc: Joerg Roedel <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Tom Lendacky <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Reviewed-by: Steve Rutherford <[email protected]> > Reviewed-by: Venu Busireddy <[email protected]> > Signed-off-by: Brijesh Singh <[email protected]> > Signed-off-by: Ashish Kalra <[email protected]> > --- > 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 338119852512..bc1b11d057fc 100644 > --- a/arch/x86/include/asm/kvm_para.h > +++ b/arch/x86/include/asm/kvm_para.h > @@ -85,6 +85,18 @@ 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); > -- > 2.17.1 >
