[syslinux] Memory upgrade breaks net boot (PXE + NFS Root)

[H. Peter Anvin]

Alex Still wrote:
> Hi list !
> 
> A memory upgrade (from 2 to 4Gb) on a bunch of IBM LS21 blades has triggered
> a very weird behavior.
> I really can't say if this could be PXE related or not - apologies if it
> isn't.
> 
> These machines start via PXE and then NFS-mount their root.
> 
> Following the upgrade, none of them would boot. I've played with the "mem="
> kernel option, and the result is :
> - if mem < 3250m : everything's fine
> - for some values of mem : Machine auto-reboots while loading the initrd
> "Loading initrd...*bam*"
> - some others : Initrd loads, but turns out it's corrupted ("can't find a
> valid initrd", then panic)
> - some others : Kernel starts booting, bnx2 driver errors all over the
> place, machine hangs during the boot process
> 
> Unfortunately I have no other hardware to try this on. We're using a 64 bits
> kernel, which should handle 4Gb fine.
> Booting from a CD works fine. At this point I can't figure out if this is
> related to PXE or the kernel (nfs-root setup)
> 
> If anyone else has seen this, I'd love to hear about it !
> 

I would start by running memtest86+ on this box.  My first guess would 
be a bad DIMM (or an overloaded memory bus), or a BIOS (SMM?) bug 
related to very large amounts of memory.

	-hpa