linux-kernel - Re: [PATCH 4/8] ACPI, APEI, Resolve false conflict between ACPI NVS and APEI

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Date:	Tue, 20 Sep 2011 22:23:29 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Len Brown <lenb@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 4/8] ACPI, APEI, Resolve false conflict between ACPI NVS
 and APEI

On Tue, Sep 20, 2011 at 7:43 PM, Huang Ying <ying.huang@...el.com> wrote:
> On 09/21/2011 12:26 AM, Bjorn Helgaas wrote:
>> On Mon, Sep 19, 2011 at 8:34 PM, Huang Ying <ying.huang@...el.com> wrote:
>>> On 09/20/2011 10:09 AM, Bjorn Helgaas wrote:
>>>> On Mon, Sep 19, 2011 at 7:38 PM, Huang Ying <ying.huang@...el.com> wrote:
>>>>> Some firmware will access memory in ACPI NVS region via APEI.  That
>>>>> is, instructions in APEI ERST/EINJ table will read/write ACPI NVS
>>>>> region.  The original resource conflict checking in APEI code will
>>>>> check memory/ioport accessed by APEI via general resource management
>>>>> mech.  But ACPI NVS region is marked as busy already, so that the
>>>>> false resource conflict will prevent APEI ERST/EINJ to work.
>>>>>
>>>>> To fix this, this patch excludes ACPI NVS regions when APEI components
>>>>> request resources.  So that they will not conflict with ACPI NVS
>>>>> regions.
>>>>
>>>> I think this is much, much too complicated.
>>>>
>>>> Yinghai's three-line e820.c patch to leave ACPI NVS regions in the
>>>> iomem_resource tree, but as not busy, is far better.
>>>
>>> ACPI NVS should only be used by firmware or firmware interpreter instead
>>> of the ordinary drivers.  So I think that is reasonable to make it busy
>>> in iomem resource tree.
>>
>> "My driver is not like ordinary drivers" is a common excuse for adding
>> special cases. I don't buy it.
>>
>> These patches (3 and 4) add a lot of complexity but I don't believe
>> they add any real protection.
>>
>> Regions are marked busy by their owners, i.e., by drivers that claim
>> devices and know how to operate them.  The e820 code is not an owner
>> of ACPI NVS regions, so it should not mark them busy.
>>
>> I don't really think we have a problem here that needs to be solved.
>> Ordinary drivers have no way of learning an address in ACPI NVS, so
>> they aren't even going to try to use it.
>
> So what resource conflict checking is for?  If something wrong with
> driver configuration, resource description in ACPI table etc, the driver
> may request iomem inside ACPI NVS regions.
>
> ACPI NVS regions already have a user, that is the ACPI AML interpreter,
> so it is always busy.

If the AML interpreter is the user, *it* should mark the regions busy, not e820.

Bjorn
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