Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?)

[Sean Christopherson]

On Tue, Jan 31, 2023, Joerg Roedel wrote:
> On Mon, Jan 30, 2023 at 09:30:38AM -0800, H. Peter Anvin wrote:
> > It's somewhat odd to me that reading %dr7 is volatile, but %dr6 is
> > not... %dr6 is the status register!
> 
> The reason is that on SEV-ES only accesses to DR7 will cause #VC
> exceptions, DR0-DR6 are not intercepted.

I don't think that is technically true.  A _well-behaved_ hypervisor will not
intercept DR0-DR6 accesses for SEV-ES guests, but AFAICT nothing in the SEV-ES
architecture enforces that behavior.