linux-kernel - Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)

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Date:   Tue, 23 Jun 2020 18:13:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <Thomas.Lendacky@....com>,
        Mike Stunes <mstunes@...are.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Juergen Gross <JGross@...e.com>,
        Jiri Slaby <jslaby@...e.cz>, Kees Cook <keescook@...omium.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        X86 ML <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP
 from userspace)

On Tue, Jun 23, 2020 at 09:03:56AM -0700, Dave Hansen wrote:
> On 6/23/20 8:52 AM, Peter Zijlstra wrote:
> > Isn't current #MC unconditionally fatal from kernel? But yes, I was
> > sorta aware people want that changed.
> 
> Not unconditionally.  copy_to_iter_mcsafe() is a good example of one
> thing we _can_ handle.

Urgh, I thought that stuff was still pending.

Anyway, the important thing is that it is fatal if we hit early NMI.
Which I think still holds.