Re: [PATCH v2 02/11] KVM: x86: emulator: introduce update_emulation_mode

Maxim Levitsky
2022-07-21T11:52:35Z

On Wed, 2022-07-20 at 23:44 +0000, Sean Christopherson wrote:
> On Tue, Jun 21, 2022, Maxim Levitsky wrote:
> > +static inline int update_emulation_mode(struct x86_emulate_ctxt *ctxt)
>
> Maybe emulator_recalc_and_set_mode()? It took me a second to understand that
> "update" also involves determining the "new" mode, e.g. I was trying to figure
> out where @mode was :-)

I don't mind at all, will update in v3.

>
> > +{
> > + u64 efer;
> > + struct desc_struct cs;
> > + u16 selector;
> > + u32 base3;
> > +
> > + ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
> > +
> > + if (!ctxt->ops->get_cr(ctxt, 0) & X86_CR0_PE) {
> > + /* Real mode. cpu must not have long mode active */
> > + if (efer & EFER_LMA)
> > + return X86EMUL_UNHANDLEABLE;
>
> If we hit this, is there any hope of X86EMUL_UNHANDLEABLE doing the right thing?
> Ah, SMM and the ability to swizzle SMRAM state. Bummer. I was hoping we could
> just bug the VM.

I just tried to be a good citizen here, it is probably impossible to hit this case.
(RSM ignores LMA bit in the EFER in the SMRAM).

Best regards,
Maxim Levitsky

>
> > + ctxt->mode = X86EMUL_MODE_REAL;
> > + return X86EMUL_CONTINUE;
> > + }