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

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Message-ID: <529905F9.30703@zytor.com>
Date:	Fri, 29 Nov 2013 13:24:09 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] Add a text_poke syscall v2

On 11/29/2013 12:35 PM, Oleg Nesterov wrote:
> On 11/29, H. Peter Anvin wrote:
>>
>> On 11/29/2013 12:05 PM, Oleg Nesterov wrote:
>>>
>>> Can't we invalidate pte (so that any user will stuck in page fault),
>>> update the page(s), restore the pte and drop the locks?
>>
>> That would require a global TLB shootdown
> 
> Well, it is not really global, it is for mm_cpumask() and for good
> reason?
> 
> And is it really worse than on_each_cpu(do_sync_core) and the usage
> of text_mutex?
> 

Probably not, but one would have to consider the total amount of
synchronization needed.

>> (and wouldn't help
>> shared-memory code segments, if we care about that at all.)
> 
> Well, I think this should only support the private mappings.
> 

Well, what do you do if someone tries this on a MAP_SHARED mapping?
Error out?

	-hpa

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