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Date: Tue, 16 Jun 2009 23:29:18 +0800
Message-ID: <2375c9f90906160829g3d605836yb4c5b9beeac50c5f@mail.gmail.com>
Subject: Re: [Patch BUGFIX] kcore: fix its wrong size on x86_64
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Tao Ma <tao.ma@oracle.com>, Andrew Morton <akpm@linux-foundation.org>,
       linux-kernel@vger.kernel.org, Alexey Dobriyan <adobriyan@gmail.com>
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On Mon, Jun 15, 2009 at 6:08 PM, Eric W. Biederman<ebiederm@xmission.com> wrote:
> Amerigo Wang <xiyou.wangcong@gmail.com> writes:
>
>> Fix wrong /proc/kcore size on x86_64.
>>
>> x86_64 uses __va() macro to caculate the virtual address passed to kclist_add()
>> but decodes it with its own macro kc_vadd_to_offset(). This is wrong.
>
> Ok.  I finally understand what is going on here, and no kc_vaddr_to_offset
> is not wrong when applied to a virtual address.  In fact I expect the current
> definition makes things a bit more predictable.
>
> And yes kclist_add is must be given a virtual address
>
>> Also, according to Documentation/x86/x86_64/mm.txt, kc_vaddr_to_offset()
>> is wrong too.
>
> How so?  The file offset is a number space that is different from both
> physical and virtual addresses.

Why? They _do_ have some calculated relations.

>
>> So just remove them, use the generic macro.
>
> I think a case can be made either way.  In practice neither answer
> gives us a dense offset space on x86_64 so I think I prefer the
> current definition which sets or clears the high bits as opposed
> to something that mangles the address more.
>

I am trying to dig more... There must be something wrong there.

>
> It uses get_kcore_size and (size_t)high_memory - PAGE_OFFSET + PAGE_SIZE;
> The second definition being bogus as it has nothing to do with which
> offsets are accepted.

Agreed. Maybe we can just remove the second one and update the doc?
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