Messages in this thread Patch in this message | | | From | Ian Campbell <> | Date | Thu, 28 Feb 2008 23:16:49 +0000 | Subject | Re: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB |
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On Thu, 2008-02-28 at 13:14 -0800, H. Peter Anvin wrote: > Ian Campbell wrote: > > On Thu, 2008-02-28 at 14:28 +0100, Alexander van Heukelum wrote: > >> Instead of using early reservations inside the kernel code, > >> we could use the realmode code to modify the e820 memmap. > >> This patch shows what that would look like. I have not looked > >> at the case where the BIOS does not provide an e820 memmap > >> yet. Probably a full solution would need to create a fake > >> e820 memmap in that case. > > > > An e820 is already faked up in machine_specific_memory_setup() if one > > doesn't already exist. > > > >> Comments? > > > > This won't work for Xen since the real-mode code never runs there. I > > think it could be fixed in xen_memory_setup() though if native goes down > > this route. > > > > s/could/should/. > > You need to set up your memory map more sensibly; it's not just the > kernel, user space tries to access these areas too.
Agreed, I think it's pure luck that Xen kernels have gotten away with it in the past.
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); return "Xen"; } -- 1.5.4.2
-- Ian Campbell
His mind is like a steel trap: full of mice. -- Foghorn Leghorn
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