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

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Date: Fri, 5 Jan 2024 11:34:05 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Rick P Edgecombe <rick.p.edgecombe@...el.com>
Cc: "jmattson@...gle.com" <jmattson@...gle.com>, Chao Gao <chao.gao@...el.com>, 
	Weijiang Yang <weijiang.yang@...el.com>, Dave Hansen <dave.hansen@...el.com>, 
	"peterz@...radead.org" <peterz@...radead.org>, "john.allen@....com" <john.allen@....com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "mlevitsk@...hat.com" <mlevitsk@...hat.com>, 
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v8 00/26] Enable CET Virtualization

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.