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    SubjectRe: [PATCH 00/03] kexec: Avoid overwriting the current pgd (V2)
    On Wed, 2006-05-24 at 18:56 -0400, Vivek Goyal wrote:
    > On Wed, May 24, 2006 at 01:40:31PM +0900, Magnus Damm wrote:
    > > kexec: Avoid overwriting the current pgd (V2)
    > >
    > > This patch updates the kexec code for i386 and x86_64 to avoid overwriting
    > > the current pgd. For most people is overwriting the current pgd is not a big
    > > problem. When kexec:ing into a new kernel that reinitializes and makes use of
    > > all memory we don't care about saving state.
    > >
    > > But overwriting the current pgd is not a good solution in the case of kdump
    > > (CONFIG_CRASH_DUMP) where we want to preserve as much state as possible when
    > > a crash occurs. This patch solves the overwriting issue.
    > >
    > > 20060524: V2
    > >
    > > - Broke out architecture-specific data structures into asm/kexec.h
    > > - Fixed a i386/PAE page table problem only triggering on real hardware.
    > > - Moved segment handling code into the assembly routines.
    > What's the advantage of moving segment handling code into assembly
    > routines? It will only add to the fear of control code page size growing
    > beyond 4K.

    I have two main reasons:

    - Why wrap assembler instructions in C code if you just can move them
    into an already existing assembly file? Much cleaner IMO.

    - I'm currently working on making kexec to work under xen/dom0. And by
    moving the segment handling code into the assembly file we reduce the
    amount of duplicated code.

    I was concerned about the size of the assembly code too and I just
    re-checked with my patches applied:

    i386: 300 / 4096 bytes used
    x86_64: 364 / 4096 bytes used

    I'd say we have more than enough space!


    / magnus

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