Re: [PATCH 41/70] x86/sev-es: Add Runtime #VC Exception Handler

[Andy Lutomirski]

On Thu, Mar 19, 2020 at 2:14 AM Joerg Roedel <joro@xxxxxxxxxx> wrote:
>
> From: Tom Lendacky <thomas.lendacky@xxxxxxx>
>
> Add the handler for #VC exceptions invoked at runtime.

If I read this correctly, this does not use IST.  If that's true, I
don't see how this can possibly work.  There at least two nasty cases
that come to mind:

1. SYSCALL followed by NMI.  The NMI IRET hack gets to #VC and we
explode.  This is fixable by getting rid of the NMI EFLAGS.TF hack.

2. tools/testing/selftests/x86/mov_ss_trap_64.  User code does MOV
(addr), SS; SYSCALL, where addr has a data breakpoint.  We get #DB
promoted to #VC with no stack.