linux-kernel - Re: [PATCH?] uprobes: change uprobe_write

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Message-ID: <529F5E47.3040108@zytor.com>
Date:	Wed, 04 Dec 2013 08:54:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH?] uprobes: change uprobe_write_opcode() to modify the
 page directly

On 12/04/2013 08:48 AM, Oleg Nesterov wrote:
> On 12/04, H. Peter Anvin wrote:
>>
>> On 12/04/2013 03:11 AM, Oleg Nesterov wrote:
>>>
>>> It is still not clear to me if we can simply change a single byte on
>>> x86 or not, but at least on powerpc we need to update 4 bytes. Perhaps
>>> we can conditionalize these pte games later.
>>>
>>
>> But 4 aligned bytes can be written as a single transaction.
> 
> Ah yes, this is true.
> 

That is why I talk about the atomic instruction word... most (but not
*all*) architectures have a fundamental minimum unit of instructions
which is aligned and can be atomically written.  Typically this is 1, 2,
or 4 bytes.

	-hpa

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