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

[Joerg Roedel]

On Fri, Jan 27, 2023 at 10:56:26PM +1100, Alexey Kardashevskiy wrote:
> https://github.com/aik/linux/commit/d0d6bbb58fcd927ddd1f8e9d42ab121920c7eafc

Okay, I reproduced the problem here and the root cause turned out to be
that the compiler moved the DR7 read instruction before the 5-byte NOP
which becomes the call to sev_es_ist_enter() in SEV-ES guests. This is
guaranteed to cause #VC exception stack recursion if the NMI was
triggered on the #VC stack, and that leads to all kinds of undefined
behavior.

Regards,

	Joerg