Re: [BUGFIX] ACPI, APEI, EINJ Param support is disabled by default

From: Huang Ying
Date: Thu Jul 21 2011 - 01:14:52 EST

On 07/21/2011 12:46 PM, Bjorn Helgaas wrote:
> On Wed, Jul 20, 2011 at 7:02 PM, Huang Ying <ying.huang@xxxxxxxxx> wrote:
>> On 07/20/2011 11:22 PM, Bjorn Helgaas wrote:
>>> On Wed, Jul 20, 2011 at 2:09 AM, Huang Ying <ying.huang@xxxxxxxxx> wrote:
>>>> EINJ parameter support is only usable for some specific BIOS.
>>>> Originally, it is expected to have no harm for BIOS does not support
>>>> it. But now, we found it will cause issue (memory overwriting) for
>>>> some BIOS. So param support is disabled by default and only enabled
>>>> when newly added module parameter named "param_extension" is
>>>> explicitly specified.
>>> Adding parameters always makes things harder for users. Is there any
>>> way this could be done with a whitelist or other automatic mechanism?
>> The only user of EINJ is RAS developer/tester. So we adopt a simpler
>> solution.
>>> Per 6e320ec1d98 (which added EINJ parameter support), parameters are
>>> an unpublished extension and are not part of the ACPI spec. So if we
>>> pick up an MMIO address from a SET_ERROR_TYPE WRITE_REGISTER
>>> instruction and blindly fill in a structure (undefined by the spec)
>>> presumed to be at that address, it doesn't seem surprising that things
>>> will blow up on BIOSes that don't expect that behavior. After all,
>>> the spec says to write to a generic address structure (not an
>>> einj_parameter structure) when we interpret the WRITE_REGISTER
>>> instruction (not at the magic time between SET_ERROR_TYPE and
>>> If EINJ parameter support is ever added to the ACPI spec, I would
>>> expect a new EINJ flag bit or similar indication to be added at the
>>> same time, so the OS would know when to use it.
>> EINJ parameter support has not been added to ACPI spec, it may be added
>> in the future, and should has some way to indicate whether parameter is
>> supported.
>>> Can you add a whitelist of BIOSes that do support this extension?
>>> Maybe you could define a GUID that future platforms could supply so
>>> you wouldn't have to update the whitelist for every new platform that
>>> supports it?
>> IMHO, the EINJ will not be used by the ordinary users. If so, can we
>> use a simpler solution such as that in this patch?
> It's not very clear to the code reader when this extension might be
> useful. It's a bit of folklore that will have to be passed around via
> word-of-mouth. If I want to modify the parameter code, I have no
> clues about what sort of machine I'd need to test it.
> What happens if you load this module on a machine that supports the
> extension, but you don't supply the module parameter? I would expect
> problems in that case, too, because the BIOS is expecting parameters
> and we won't fill them in.

On my testing machine with parameter extension, if no injecting
parameter is specified, some BIOS specified default parameter will be used.

> But maybe you're right that this is so specialized that we shouldn't
> over-engineer it.

Best Regards,
Huang Ying
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