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

[Sean Christopherson <seanjc@google.com>]

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 :-)

> +{
> +	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.

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