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

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Message-ID: <20121103163301.GA9496@redhat.com>
Date:	Sat, 3 Nov 2012 17:33:01 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.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 10/29, Ananth N Mavinakayanahalli wrote:
>
> On Fri, Oct 26, 2012 at 06:39:51PM +0200, Oleg Nesterov wrote:
> > >
> > > > 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.
> >
> > This is bad...
> >
> > flush_icache_user needs vma. perhaps just to check VM_EXEC...
> >
> > So let me repeat to be sure I really understand, do you confirm that
> > _in general_ flush_dcache_page() is not enough?
>
> flush_dcache_page() on powerpc already checks for
> CPU_FTR_COHERENT_ICACHE. So, yes, that is enough.

Thanks Ananth.

Still it is not clear to me if flush_dcache_page() would be always right
if we add the new port.

OK. So I assume we need the fix and I am going to apply the patch below.

Ananth, Rabin, will you ack it (including the comment I affed) ?

Oleg.

------------------------------------------------------------------------------
[PATCH] uprobes: flush cache after xol write

From: Rabin Vincent <rabin@....in>

Flush the cache so that the instructions written to the XOL area are
visible.

Signed-off-by: Rabin Vincent <rabin@....in>

--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -1199,6 +1199,11 @@ static unsigned long xol_get_insn_slot(s
 	vaddr = kmap_atomic(area->page);
 	memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
 	kunmap_atomic(vaddr);
+	/*
+	 * We probably need flush_icache_user_range() but it needs vma.
+	 * This should work on supported architectures too.
+	 */
+	flush_dcache_page(area->page);
 
 	return current->utask->xol_vaddr;
 }

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