Re: [PATCH v1 4/6] KVM: x86: Add emulator helper for LASS violation check

[Zeng Guang]

On 6/28/2023 2:28 AM, Sean Christopherson wrote:
> On Thu, Jun 01, 2023, Zeng Guang wrote:
> > When LASS is enabled, KVM need apply LASS violation check to instruction
> > emulations. Add helper for the usage of x86 emulator to perform LASS
> > protection.
> >
> > Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
> > Tested-by: Xuelian Guo <xuelian.guo@xxxxxxxxx>
> > ---
> >   arch/x86/kvm/kvm_emulate.h |  1 +
> >   arch/x86/kvm/x86.c         | 12 ++++++++++++
> >   2 files changed, 13 insertions(+)
> >
> > diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
> > index f1439ab7c14b..fd1c2b22867e 100644
> > --- a/arch/x86/kvm/kvm_emulate.h
> > +++ b/arch/x86/kvm/kvm_emulate.h
> > @@ -230,6 +230,7 @@ struct x86_emulate_ops {
> >   	int (*leave_smm)(struct x86_emulate_ctxt *ctxt);
> >   	void (*triple_fault)(struct x86_emulate_ctxt *ctxt);
> >   	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
> > +	bool (*check_lass)(struct x86_emulate_ctxt *ctxt, u64 access, u64 la, u32 flags);
> >   };
> >   
> >   /* Type, address-of, and value of an instruction's operand. */
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index c0778ca39650..faf01fecc4ca 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -8287,6 +8287,17 @@ static void emulator_vm_bugged(struct x86_emulate_ctxt *ctxt)
> >   		kvm_vm_bugged(kvm);
> >   }
> >   
> > +static bool emulator_check_lass(struct x86_emulate_ctxt *ctxt,
> > +				u64 access, u64 la, u32 flags)
> > +{
> > +	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
> > +
> > +	if (!is_long_mode(vcpu))
> > +		return false;
> Likely a moot point if we wrap ->gva_to_gpa(), but most this into the vendor
> implementation.
It's right way to move cpu mode check into is_lass_violation(). 
Previously I was struggling
to expect getting benefit from separate invocation. But it doesn't help 
much indeed.

> And if we keep these emulator hooks, massage the patch ordering:
>
>    1. Add plumbing to emulator to pass new flags
>    2. Add kvm_x86_ops definition and invocation from emulator
>    3. Implement and wire up vmx_is_lass_violation()
>
> That way the changes to each area of KVM are better isolated.
OK. Will reorganize the patch accordingly.
Thanks.
> > +	return static_call(kvm_x86_check_lass)(vcpu, access, la, flags);
> > +}
> > +
> >   static const struct x86_emulate_ops emulate_ops = {
> >   	.vm_bugged           = emulator_vm_bugged,
> >   	.read_gpr            = emulator_read_gpr,
> > @@ -8332,6 +8343,7 @@ static const struct x86_emulate_ops emulate_ops = {
> >   	.leave_smm           = emulator_leave_smm,
> >   	.triple_fault        = emulator_triple_fault,
> >   	.set_xcr             = emulator_set_xcr,
> > +	.check_lass          = emulator_check_lass,
> >   };
> >   
> >   static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
> > --
> > 2.27.0