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    SubjectRe: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB
    On Thu, Feb 28, 2008 at 11:16:49PM +0000, Ian Campbell wrote:
    >
    > The patch below seems like the right thing to do. It certainly boots in
    > a domU without the DMI problem (without any of the other related patches
    > such as Alexander's).
    >
    > However ddcprobe hangs when run -- need to investigate some more, vm86
    > in general works ok (i.e. my vm86 test code passes).
    >
    > BTW Jeremy, the kernel doesn't use XENMEM_memory_map -- any reason other
    > than it not being useful at the time? These days the tools can push an
    > arbitrary e820 down for a guest which might be useful to support,
    > although nothing interesting is done with it today.
    >
    > Ian.
    >
    > x86/xen: Construct e820 map with a hole between 640K-1M.
    >
    > Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Ingo Molnar <mingo@redhat.com>
    > Cc: H. Peter Anvin <hpa@zytor.com>
    > Cc: Jeremy Fitzhardinge <jeremy@goop.org>
    > ---
    > arch/x86/xen/setup.c | 3 ++-
    > 1 files changed, 2 insertions(+), 1 deletions(-)
    >
    > diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
    > index 3bad477..2341492 100644
    > --- a/arch/x86/xen/setup.c
    > +++ b/arch/x86/xen/setup.c
    > @@ -38,7 +38,8 @@ char * __init xen_memory_setup(void)
    > unsigned long max_pfn = xen_start_info->nr_pages;
    >
    > e820.nr_map = 0;
    > - add_memory_region(0, PFN_PHYS(max_pfn), E820_RAM);
    > + add_memory_region(0, LOWMEMSIZE(), E820_RAM);
    > + add_memory_region(HIGH_MEMORY, PFN_PHYS(max_pfn)-HIGH_MEMORY, E820_RAM);

    Won't this waste 300+ KB of Perfectly Good RAM? Or I understood it
    incorrectly?

    I am aware that it would take more work to tell all kernel code that it
    shouldn't look for BIOS data on this region when running as a domU guest,
    but it seems that it would be a better solution.

    --
    Eduardo


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