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

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Message-ID: <20121025145839.GB26929@redhat.com>
Date:	Thu, 25 Oct 2012 16:58:39 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rabin Vincent <rabin@....in>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc:	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 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?

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?

Oleg.

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