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Date: Tue, 28 Oct 2014 21:12:21 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: Peter Zijlstra <peterz@infradead.org>, Kirill Tkhai <ktkhai@parallels.com>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH 2/3] introduce probe_slab_address()
Message-ID: <20141028201221.GA2106@redhat.com>
References: <1413962231.19914.130.camel@tkhai> <20141027195339.GA11736@redhat.com> <20141027195425.GC11736@redhat.com> <1414475091.8574.6.camel@tkhai> <20141028150102.GP3219@twins.programming.kicks-ass.net> <544FD8C6.5020606@yandex.ru> <20141028195542.GA1352@redhat.com>
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On 10/28, Oleg Nesterov wrote:
>
> On 10/28, Kirill Tkhai wrote:
> >
> > Yes, probe_kernel_read() is in [1/3], but it's not the same as
> > __probe_kernel_read() for blackfin, for example.
> >
> > It's defined as
> >
> > long __weak probe_kernel_read(void *dst, const void *src, size_t size)
> >     __attribute__((alias("__probe_kernel_read")));
> >
> > But blackfin's probe_kernel_read() redefines this __weak function,
> > isn't it? Didn't get_freepointer_safe() use to call architecture's
> > probe_kernel_read() before?
>
> I _think_ that __probe_kernel_read(slab_ddr) should be fine.
>
> Yes, an architecture may want to reimplement probe_kernel_read() to
> allow to safely access the special areas, or special addresses.
>
> But again, in this case we know that this address points to the
> "normal" kernel memory, __copy_from_user_inatomic() should work fine.

OTOH, perhaps probe_kernel_address() should use probe_kernel_read(), not
__probe_kernel_read(). But currently it just calls __copy_inatomic() so
1/3 follows this logic.

Oleg.