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    SubjectRe: [PATCHv7 02/14] mm: Add support for unaccepted memory
    On Thu, Sep 22, 2022 at 09:31:12AM -0500, Tom Lendacky wrote:
    > On 9/8/22 14:28, Mike Rapoport wrote:
    > > On Thu, Sep 08, 2022 at 09:23:07AM -0700, Dionna Amalie Glaze wrote:
    > > > >
    > > > > Looks like the first access to the memory map fails, although I think
    > > > > it's not in INIT_LIST_HEAD() but rather in init_page_count().
    > > > >
    > > > > I'd start with making sure that page_alloc::memmap_alloc() actually returns
    > > > > accepted memory. If you build kernel with CONFIG_DEBUG_VM=y the memory map
    > > > > will poisoned in this function, so my guess is it'd crash there.
    > > > >
    > > >
    > > > That's a wonderful hint, thank you! I did not run this test
    > > > CONFIG_DEBUG_VM set, but you think it's possible it could still be
    > > > here?
    > >
    > > It depends on how you configured your kernel. Say, defconfig does not set
    > > it.
    > >
    >
    > I also hit the issue at 256GB. My config is using CONFIG_SPARSEMEM_VMEMMAP
    > and fails in memmap_init_range() when attempting to add the first PFN. It
    > looks like the underlying page that is backing the vmemmap has not been
    > accepted (I receive a #VC 0x404 => page not validated).
    >
    > Kirill, is this a path that you've looked at? It would appear that somewhere
    > in the vmemmap_populate_hugepages() path, some memory acceptance needs to be
    > done for the pages that are used to back vmemmap. I'm not very familiar with
    > this code, so I'm not sure why everything works for a guest with 255GB of
    > memory, but then fails for a guest with 256GB of memory.

    Hm. I don't have machine that large at hands at the moment. And I have not
    looked at the codepath before.

    I will try to look into the issue.

    --
    Kiryl Shutsemau / Kirill A. Shutemov

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