Re: [PATCH v8 00/26] Enable CET Virtualization

[Sean Christopherson]

On Fri, Jan 05, 2024, Rick P Edgecombe wrote:
> On Fri, 2024-01-05 at 10:09 -0800, Jim Mattson wrote:
> > > 3. Task switching
> > 
> > Sigh. KVM is forced to emulate task switch, because the hardware is
> > incapable of virtualizing it. How hard would it be to make KVM's
> > task-switch emulation CET-aware?
> 
> (I am not too familiar with this part of the arch).
> 
> See SDM Vol 3a, chapter 7.3, number 8 and 15. The behavior is around
> actual task switching. At first glance, it looks annoying at least. It
> would need to do a CMPXCHG to guest memory at some points and take care
> to not implement the "Complex Shadow-Stack Updates" behavior.
> 
> But, would anyone use it? I'm not aware of any 32 bit supervisor shadow
> stack support out there. So maybe it is ok to just punt to userspace in
> this case?

Yeah, I think KVM can punt.