Re: [PATCH 1/10] Cr4 is valid on some 486s

[Dave Jones <davej@redhat.com>]

On Fri, Nov 11, 2005 at 12:22:07PM -0800, Linus Torvalds wrote:
 > 
 > 
 > On Fri, 11 Nov 2005, Zachary Amsden wrote:
 > > 
 > > Yes, this is fine, but is it worth writing the feature discovery code?  I
 > > suppose it doesn't matter, as it gets jettisoned after init.  I guess it is
 > > just preference.
 > 
 > Well, you could do the feature discovery by trying to take a fault early 
 > at boot-time. That's how we verify that write-protect works, and how we 
 > check that math exceptions come in the right way..
 > 
 > > Could we consider doing the same with LOCK prefix for SMP kernels booted on
 > > UP?  Evil grin.
 > 
 > Not so evil - I think it's been discussed. Not with alternates (not worth 
 > it), but it wouldn't be hard to do: just add a new section for "lock 
 > address", and have each inline asm that does a lock prefix do basically
 > 
 > 	1:
 > 		lock ; xyzzy
 > 
 > 	.section .lock.address
 > 	.long 1b
 > 	.previous
 > 
 > and then just walk the ".lock.address" thing and turn all locks into 0x90 
 > (nop).

Looks like the Ubuntu people already did this...

http://www.kernel.org/git/?p=linux/kernel/git/bcollins/ubuntu-2.6.git;a=commitdiff;h=048985336e32efe665cddd348e92e4a4a5351415;hp=1cb630c2b5aaad7cedaa78aa135e6cecf5ab91ac

		Dave