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

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Message-ID: <20131130145642.GB15790@redhat.com>
Date:	Sat, 30 Nov 2013 15:56:42 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.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, H. Peter Anvin wrote:
>
> 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.

Yes, agreed, this should be justified.

> >> (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?

Imho yes. But this needs more discussion, and afaics this is a bit
offtopic.

Please note that this patch relies on bp_target_mm, this can't help
in VM_SHARED case too.

Oleg.

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