linux-kernel - Re: [PATCH] Add a text

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Message-ID: <20131127231305.GN32267@pd.tnic>
Date:	Thu, 28 Nov 2013 00:13:05 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Add a text_poke syscall v2

On Wed, Nov 27, 2013 at 03:04:41PM -0800, Linus Torvalds wrote:
> So sysexit/sysret doesn't count as a serializing instruction, no.
> But it doesn't need to, because *self*-modifying code doesn't need a
> serializing instruction, only a branch. It's only *cross*-modifying
> code that needs a serializing instruction.
>
> So the IPI is sufficient for the cross-modifying case, and the sysret
> is sufficient for the self-modifying case. And we also don't need
> to worry about "what happens if we schedule to another CPU, and
> self-modifying becomes cross-modifying", because the scheduling will
> then do the serializing instruction.
>
> So IPI for other CPU's (limited to the mm-mask) and just a system call
> for local CPU should be perfectly fine.

Cool, so basically an empty dummy syscall IPI-ed to all cores. With a
big fat comment on top.

:-)

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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