Re: [PATCH] kexec: fix 64Gb limit on x86 w/ PAE

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Apr 09, 2010 at 08:17:49AM -0400, Neil Horman wrote:
> Version 2, with Simons consistency fixes and cleanups
> 
> Fix up x86 kexec to exclude memory on i686 kernels beyond 64GB limit
> 
> We found a problem recently on x86 systems.  If a 32 bit PAE enabled system
> contains more then 64GB of physical ram, the kernel will truncate the max_pfn
> value to 64GB.  Unfortunately it still leaves all the physical memory regions
> present in /proc/iomem.  Since kexec builds its elf headers based on
> /proc/iomem the elf headers indicate the size of memory is larger than what the
> kernel is willing to address.  The result is that, during a copy of
> /proc/vmcore, a read will return -EFAULT when the requested offset is beyond the
> 64GB range, leaving the seemingly truncated vmcore useless, as the elf headers
> indicate memory beyond what the file contains.
> 
> The fix for it is pretty straightforward, just ensure that, when on x86 systems,
> we don't record any entries in the memory_range array that cross  the 64Gb mark.
> This keeps us in line with the kernel and lets the copy finish sucessfully,
> providing a workable core
> 
> Tested successfully by myself
> Originally-authored-by: Dave Anderson <anderson@redhat.com>
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> 
> 
>  crashdump-x86.c |   15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> index 9d37442..9d35b3e 100644
> --- a/kexec/arch/i386/crashdump-x86.c
> +++ b/kexec/arch/i386/crashdump-x86.c
> @@ -34,6 +34,12 @@
>  #include "crashdump-x86.h"
>  #include <x86/x86-linux.h>
>  
> +/*
> + * This defines the the last address that we can support access to
> + * with a PAE enabled kernel
> + */
> +#define 64G_LIMIT 0xfffffffff
> +
>  extern struct arch_options_t arch_options;
>  
>  /* Forward Declaration. */
> @@ -114,6 +120,15 @@ static int get_crash_memory_ranges(struct memory_range **range, int *ranges,
>  		if (end <= 0x0009ffff)
>  			continue;
>  
> +		/*
> +		 *  Exclude any segments starting at or beyond 64GB, and
> +		 *  restrict any segments from ending at or beyond 64GB.
> +		 */
> +		if (start > 64GB_LIMIT)
> +			continue;
> +		if (end > 64GB_LIMIT)
> +			end = 64GB_LIMIT;
> +

Looks good to me.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Vivek
>  		crash_memory_range[memory_ranges].start = start;
>  		crash_memory_range[memory_ranges].end = end;
>  		crash_memory_range[memory_ranges].type = type;

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