linux-kernel - Re: [PATCH] BISECTED x86: avoid qword access in memcpy

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Date:	Wed, 21 Jul 2010 19:33:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	James Smart <james.smart@...lex.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH] BISECTED x86: avoid qword access in memcpy_*io

Yes, that would make sense.

"Hidetoshi Seto" <seto.hidetoshi@...fujitsu.com> wrote:

>(2010/07/21 11:48), H. Peter Anvin wrote:
>> On 07/20/2010 06:21 PM, Hidetoshi Seto wrote:
>>> With v2.6.35-rc5, my x86-64 server doesn't boot but reports a
>>> Completer Abort on lpfc card.
>>>
>>> The result of git-bisect is:
>>>   6175ddf06b6172046a329e3abfd9c901a43efd2e is the first bad commit
>>>   commit 6175ddf06b6172046a329e3abfd9c901a43efd2e
>>>   Author: Brian Gerst <brgerst@...il.com>
>>>   Date:   Fri Feb 5 09:37:07 2010 -0500
>>>     x86: Clean up mem*io functions.
>>>
>>> What I found are:
>>>  - memcpy for 64bit uses movq if count >= 64 (arch/x86/lib/memcpy_64.S)
>>>  - memcpy_toio and memcpy_fromio have changed to use this memcpy by
>>>    the above commit.
>>>  - my debug shows that lpfc calls memcpy_toio with not-qword-aligned
>>>    addresses and count >= 64, e.g.:
>>>      memcpy_toio(0xffffc900118de004, 0xffff88047293d614, 124);
>>>    and it seems that it comes from:
>>>    [drivers/scsi/lpfc/lpfc_sli.c]
>>>     4929   /* First copy mbox command data to HBA SLIM, skip past first
>>>     4930      word */
>>>     4931   to_slim = phba->MBslimaddr + sizeof (uint32_t);
>>>     4932   lpfc_memcpy_to_slim(to_slim, &mb->un.varWords[0],
>>>     4933               MAILBOX_CMD_SIZE - sizeof (uint32_t));
>>>
>>> Still I'm not sure what is wrong in software or hardware, however
>>> I suppose that qword access to iomem is not always safe, so it will
>>> be OK to back to use __inline_memcpy which uses movsl.
>>>
>>> I confirmed that my server (w/ lpfc) boots with 35-rc5 + this patch.
>>>
>>> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
>> 
>> A driver should not use the memcpy-like instructions if it isn't set up
>> to act as memory (meaning it can handle arbitrary byte enables.)
>
>So then is this a problem of lpfc driver?
>James, could you agree on that?
>
>> The function it should be using is called, fairly counterintuitively,
>> __iowrite32_copy().  It really should be called memcpy_toio32() or
>> something similar.
>> 
>> 	-hpa
>
>It seems that lpfc already implemented lpfc_memcpy_{to,from}_slim()
>as such memcpy_*io32, but limited use of it to on big endian platforms
>only.  Now lpfc can move to use it always, right?
>
>
>Thanks,
>H.Seto
>

-- 
Sent from my mobile phone.  Please pardon any lack of formatting.
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