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

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Date:	Thu, 22 Jul 2010 10:23:11 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	"H. Peter Anvin" <hpa@...or.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

(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

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