Date: Fri, 26 Oct 2012 18:39:51 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Rabin Vincent <rabin@rab.in>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Peter Zijlstra <peterz@infradead.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: [PATCH 6/9] uprobes: flush cache after xol write
Message-ID: <20121026163951.GA17742@redhat.com>
References: <1350242593-17761-1-git-send-email-rabin@rab.in> <1350242593-17761-6-git-send-email-rabin@rab.in> <20121015165756.GA11737@redhat.com> <CAH+eYFAv=UTZ1gQ5jXq8_ziNy1i3BL9y1bOUWMdTow=i3N0n+g@mail.gmail.com> <20121025145839.GB26929@redhat.com> <20121026055239.GA4862@in.ibm.com>
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On 10/26, Ananth N Mavinakayanahalli wrote:
>
> On Thu, Oct 25, 2012 at 04:58:39PM +0200, Oleg Nesterov wrote:
> > On 10/16, Rabin Vincent wrote:
> > >
> > > >> --- 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.

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?

Oleg.

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