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    SubjectRe: [PATCH] x86, efi: Delete efi_ioremap() and fix CONFIG_X86_32 oops
    On 02/20/2012 05:30 AM, Matt Fleming wrote:
    > Despite first impressions, it's not possible to use ioremap_cache() to
    > map all cached memory regions on CONFIG_X86_64 because of the way that
    > the memory map might be configured as detailed in the following bug
    > report,
    > Therefore, we need to ensure that any regions requiring a runtime
    > mapping are covered by the direct kernel mapping table. Previously,
    > this was taken care of by efi_ioremap() but if we handle this case
    > earlier, in setup_arch(), we can delete the CONFIG_X86_32 and
    > CONFIG_X86_64 efi_ioremap() implementations entirely.

    I went through the bug report but it's not entirely clear to me what the
    fundamental root cause of the problem is, as opposed to what are
    symptoms. We need to straighten this out, and we need to do so fairly soon.

    It would seem logical that we include in the kernel memory mapping the
    regions we need, and *ONLY* the regions necessary; in particular we
    shouldn't include *any* memory holes except for the < 1 MiB legacy
    region (which is okay because of fixed MTRRs, but even that should be
    eventually nuked. That will require driver work hough.)

    As I said, in a lot of ways the right thing would be for ioremap() to
    manifest mappings in the standard 1:1 position, but when I very very
    briefly looked at it it look ed like that would require core changes
    which probably makes it too much work.


    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.

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