linux-kernel - Re: [PATCH 2/3] introduce probe_slab

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Date:	Tue, 28 Oct 2014 21:12:21 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Kirill Tkhai <ktkhai@...allels.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 2/3] introduce probe_slab_address()

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.

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