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

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Apr 09, 2010 at 08:32:48AM +1000, Simon Horman wrote:
> On Thu, Apr 08, 2010 at 12:46:44PM -0400, Neil Horman wrote:
> > 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
> 
> Hi Neil,
> 
> This seems reasonable to me.
> 
> > Tested successfully by myself
> > Originally-authored-by: Dave Anderson <anderson@redhat.com>
> > Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> > 
> > diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
> > index 9d37442..85879a9 100644
> > --- a/kexec/arch/i386/crashdump-x86.c
> > +++ b/kexec/arch/i386/crashdump-x86.c
> > @@ -114,6 +114,15 @@ 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 >= 0x1000000000)
> > +			continue;
> > +		if (end >= 0x1000000000)
> > +			end = 0xfffffffff;
> > +
> 
> Nit picking...
> 
> Might it be better to use 0xfffffffff (or 0x1000000000) consistently?
> 
> 		if (start > 0xfffffffff)
> 			continue;
> 		if (end > 0xfffffffff)
> 			end = 0xfffffffff;
> 
Not sure what you mean by consistent here?  It seems we are using it
consistently in this patch.  Or are you referring to updating the function as a
whole?

> Or even make 0xfffffffff (or 0x1000000000) a #define ?
Yeah, that makes sense.  If you can clarify your above point on consistency, I
can repost.

thanks
Neil

> 
> >  		crash_memory_range[memory_ranges].start = start;
> >  		crash_memory_range[memory_ranges].end = end;
> >  		crash_memory_range[memory_ranges].type = type;
> > 
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> 

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec