linux-kernel - Re: [PATCH 6/9] uprobes: flush cache after xol write

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Message-ID: <20121026055239.GA4862@in.ibm.com>
Date:	Fri, 26 Oct 2012 11:22:39 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Rabin Vincent <rabin@....in>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 6/9] uprobes: flush cache after xol write

On Thu, Oct 25, 2012 at 04:58:39PM +0200, Oleg Nesterov wrote:
> On 10/16, Rabin Vincent wrote:
> >
> > 2012/10/15 Oleg Nesterov <oleg@...hat.com>:
> > > On 10/14, Rabin Vincent wrote:
> > >> Flush the cache so that the instructions written to the XOL area are
> > >> visible.
> > >>
> > >> Signed-off-by: Rabin Vincent <rabin@....in>
> > >> ---
> > >>  kernel/events/uprobes.c |    1 +
> > >>  1 file changed, 1 insertion(+)
> > >>
> > >> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > >> index ca000a9..8c52f93 100644
> > >> --- a/kernel/events/uprobes.c
> > >> +++ b/kernel/events/uprobes.c
> > >> @@ -1246,6 +1246,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
> > >>       offset = current->utask->xol_vaddr & ~PAGE_MASK;
> > >>       vaddr = kmap_atomic(area->page);
> > >>       arch_uprobe_xol_copy(&uprobe->arch, vaddr + offset);
> > >> +     flush_dcache_page(area->page);
> > >>       kunmap_atomic(vaddr);
> > >
> > > I agree... but why under kmap_atomic?
> >
> > No real reason; I'll move it to after the unmap.
> 
> OK. I assume you will send v2.
> 
> But this patch looks like a bugfix, flush_dcache_page() is not a nop
> on powerpc. So perhaps we should apply this fix right now?

Starting Power5, all Power processers have coherent caches.

> OTOH, I do not understand this stuff, everything is nop on x86. And
> when I look into Documentation/cachetlb.txt I am starting to think
> that may be this needs flush_icache_user_range instead?
>
> Rabin, Ananth could you clarify this?

Yes. We need flush_icache_user_range(). Though for x86 its always been a
nop, one never knows if there is some Power4 or older machine out there
that is still being used. We are fine for Power5 and later.

Ananth

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