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    SubjectRe: [PATCH part4 2/4] x86, acpica, acpi: Try to find if SRAT is overrided earlier.
    On 08/10/2013 07:34 AM, Yinghai Lu wrote:
    > On Fri, Aug 9, 2013 at 2:41 AM, Tang Chen<> wrote:
    >> On 08/09/2013 12:29 AM, Yinghai Lu wrote:
    >> ......
    >>> Please check if you can reuse first half of my patchset, so find and copy
    >>> override table earlier. the copied acpi tables could be near kernel code
    >>> range.
    >> I don't think we need to do the finding step at that early time, in
    >> head64.c stage.
    >> Before pagetables are setup, we can use early_ioremap() to map the
    >> memory we want to access. We don't need to use phys addr. We can do
    >> it in setup_arch(), which has nothing to do with 32bit or 64bit.
    > if override the acpi tables early, you don't need to check firmware srat and
    > then override srat.
    > just check last one will be used by kernel.
    > So you don't need to dig initrd to find srat anymore.

    The current logic is find tables in firmware, and override them. I
    don't think it is a big deal.

    Even if we want to override first, and then skip the table in
    firmware (install one time), we still don't need to do it in head64.c,
    right ?

    >>> Move finding in head64.c stage could help xen/dom0 a bit.
    >>> as Konrad is working on patchset with acpi override in xen hypervisor.
    >>> We can avoid override acpi table two times. Esp xen like to change
    >>> DMAR to XMAR.
    >> Would you please give some more info about this, and explain why finding
    >> override tables in head64.c stage is helpful for xen ?
    > xen usually can change acpi tables and pass to dom0 kernel. like change DMAR
    > to hide it to dom0 kernel.
    > also distribution could have same kernel to support bare metal and dom0.
    > so if we find the override kernel early in head64.c, dom0 path will not copy
    > actually as no one try to find that for them.

    I don't know the detail, but seeing from your description, doing
    override in head64.c may avoid a copy. If doing such a copy in xen
    is not that difficult, I think we can do it for now. Modifying
    acpi_initrd_override() logic will need to modify a lot of things.

    Just like the local node pagetable, I think it is better to do
    xen things after memory hotplug is done.


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