Re: [PATCH v1 3/4] KVM: VMX: Handle the immediate form of MSR instructions

[Xin Li]

On 7/31/2025 4:04 AM, Chao Gao wrote:
> On Wed, Jul 30, 2025 at 10:46:04AM -0700, Xin Li (Intel) wrote:
> > Handle two newly introduced VM exit reasons associated with the
> > immediate form of MSR instructions.
> >
> > For proper virtualization of the immediate form of MSR instructions,
> > Intel VMX architecture adds the following changes:
>
> The CPUID feature bit also indicates support for the two new VM-exit reasons.
> Therefore, KVM needs to reflect EXIT_REASON_MSR_READ/WRITE_IMM VM-exits to
> L1 guests in nested cases if KVM claims it supports the new form of MSR
> instructions.

Damn, forgot about nested...

> I'm also wondering if the emulator needs to support this new instruction. I
> suppose it does.

Yes, I thought about it.  However the new instructions use the VEX
prefix, which KVM doesn't support today.