linux-kernel - Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync

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Message-ID: <CA+55aFyHptQ3=gjXA_LGGkvOgsRB9FBXvCT56fG4UqcFV4wFsA@mail.gmail.com>
Date:   Fri, 2 Dec 2016 10:27:29 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Peter Anvin <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>,
        Henrique de Moraes Holschuh <hmh@....eng.br>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation

On Fri, Dec 2, 2016 at 10:03 AM, Borislav Petkov <bp@...nel.org> wrote:
>
> SNB:
> * before:
> * after:

I suspect it's entirely invisible on raw hardware. But quite possibly
more noticeable in a VM that takes slow faults for every case.

But yes, even there is' probably not *that* noticeable.

I'd prefer to get rid of them just because I don't like voodoo
programming. If there is no actual reason for "sync_core()", we
shouldn't have one there. Even if it were entirely free and the
compiler optimized it away because the compiler was so smart that it
would see that it's pointless, it's misleading and wrong on a source
level.

That is, of course, assuming that there  is no really subtle reason
why that stupid sync_core() is there.

      Linus