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    SubjectRe: [PATCH] memory hotadd fixes [4/5] avoid check in acpi
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    On Fri, 2006-08-04 at 12:13 +0900, KAMEZAWA Hiroyuki wrote:
    > On Thu, 03 Aug 2006 20:00:08 -0700
    > keith mannthey <kmannth@us.ibm.com> wrote:
    >
    >
    > > > > What protecting is there for calling add_memory on an already present
    > > > > memory range?
    > > > >
    > > > For example, considering ia64, which has 1Gbytes section...
    > >
    > > Maybe 1gb sections is too large?
    > >
    > ia64 machines sometimes to have crazy big memory...so 1gb section is requested.
    > Configurable section_size for small machines was rejected in old days.

    My HW supports about 512gb......

    What if you add a partial section. Then online in sysfs and add another
    section? messy....
    >
    > > > hot add following region.
    > > > ==
    > > > (A) 0xc0000000 - 0xd7ffffff (section 3)
    > > > (B) 0xe0000000 - 0xffffffff (section 3)
    > > > ==
    > > > (A) and (B) will go to the same section, but there is a memory hole between
    > > > (A) and (B). Considering memory (B) appears after (A) in DSDT.
    > > >
    > > > After add_memory() against (A) is called, section 3 is ready.
    > > > Then, pfn_valid(0xe0000000) and pfn_valid(0xffffffff) returns true because
    > > > they are in section 3.
    > > > So, checking pfn_valid() for (B) will returns true and memory (B) cannot be
    > > > added. ioresouce collision check will help this situation.
    > >
    > > With iommus out there throwing aliment all off way the flexability is
    > > good.
    > >
    > > My question is this.
    > >
    > > Assuming 0-0xbfffffff is present.
    > >
    > > What keeps 0xa0000000 to 0xa1000000 from being re-onlined by a bad call
    > > to add_memory?
    >
    > Usual sparsemem's add_memory() checks whether there are sections in
    > sparse_add_one_section(). then add_pages() returns -EEXIST (nothing to do).
    > And ioresouce collision check will finally find collision because 0-0xbffffff
    > resource will conflict with 0xa0000000 to 0xa10000000 area.
    > But, x86_64 's (not sparsemem) add_pages() doen't do collision check, so it panics.

    I have paniced with your 5 patches while doing SPARSMEM.... I think
    your 6th patch address the issues I was seeing.

    Thanks,
    Keith

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