linux-kernel - Re: [PATCH v5 3/6] x86/sev-es: Split up runtime #VC handler for correct state tracking

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Message-ID: <YMpKim/3Dc41xvF7@8bytes.org>
Date:   Wed, 16 Jun 2021 21:01:30 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v5 3/6] x86/sev-es: Split up runtime #VC handler for
 correct state tracking

Hi Peter,

sorry, missed this email before sending out v6.

On Wed, Jun 16, 2021 at 06:04:26PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 14, 2021 at 03:53:24PM +0200, Joerg Roedel wrote:
> >  _ASM_NOKPROBE(\asmsym)
> >  SYM_CODE_END(\asmsym)
> 
> Consistency with idtentry_mce_db would seem to suggest using \cfunc and
> noist_\cfunc.
> 
> amluto, tglx: do we have strong feelings on consistency?

Yeah, but this distinction does not make sense here, as none of the #VC
handlers C functions run on the actual #VC IST stack. The from-kernel
function might run on the fall-back stack (not really possible today
unless the hypervisor does something nasty). And the difference between
the fall-back stack and the actual IST stack is, that on the fall-back
stack nesting #VC exceptions is still supported.

> > +	vc_handle_trap_db(regs);
> 
> It's a bit sad this does user_mode(regs) again.

Okay, I will change this according your comments.

Thanks,

	Joerg