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    SubjectRe: [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@intel.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@intel.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@intel.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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