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

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Message-ID: <20161202185008.tdziqrzi4a3axord@pd.tnic>
Date:   Fri, 2 Dec 2016 19:50:08 +0100
From:   Borislav Petkov <bp@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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 02, 2016 at 10:27:29AM -0800, Linus Torvalds wrote:
> That is, of course, assuming that there  is no really subtle reason
> why that stupid sync_core() is there.

Right, we can try to do something like invalidate_icache() or so in
there with the JMP so that the BSP refetches modified code and see where
it gets us.

The good thing is, the early patching paths run before SMP is
up but from looking at load_module(), for example, which does
post_relocation()->module_finalize()->apply_alternatives(), this can
happen late.

Now there I'd like to avoid other cores walking into that address being
patched. Or are we "safe" there in the sense that load_module() happens
on one CPU only sequentially? (I haven't looked at that code to see
what's going on there, actually).

-- 
Regards/Gruss,
    Boris.

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