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

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Message-ID: <20200623161010.GE32590@zn.tnic>
Date:   Tue, 23 Jun 2020 18:10:10 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        Dave Hansen <dave.hansen@...el.com>,
        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 04:32:22PM +0100, Andrew Cooper wrote:
> MSR_MCG_STATUS.MCIP, and yes - any #MC before that point will
> immediately Shutdown.  Any #MC between that point and IRET will clobber
> its IST stack and end up sad.

Well, at some point we should simply accept that we're living a little
on the edge. That is, until we get IRET with a mask of to-reenable
vectors which has #MC, NMI and whatever else vectors. It would be even
better if that mask were configurable.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette