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


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).

Linus
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