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SubjectRe: [BUG] x86 kenel won't boot under Virtual PC


On Fri, 5 Sep 2008, Jan Beulich wrote:
>
> I disagree here: If I configure a 686+ kernel, I expect these NOPs to be
> that way (and to work). If you want to run on something that's not
> compliant, you just shouldn't configure your kernel that way.

Well, if you actually do a

git grep 'ASM_NOP[0-9]'

you'll find that just the _definitions_ of those things are the bulk of it
BY FAR, and that there doesn't seem to be a single user that cares even
remotely about performance.

So I actually think that the whole thing is a waste of time. We should
probably

- pick a single set of NOP's per 32-bit/64-bit (since the good nops in
32-bit aren't 64-bit instructions at all, so we do want different nops
depending on _that_)

The whole static choice by microarchitecture is pure garbage.

- Probably also just declare that those default nops are single
instructions, just so that we never even have to think about it from a
dynamic replacement angle.

Look at the uses again, and realize that it really is just pure garbage
to have this kind of complex and subtle stuff going on.

- Move the optimized nop definitions (K7_NOPx etc) to the only place that
cares - asm/x86/kernel/alternative.c. When we do things _dynamically_,
it can actually make sense to pick a nop more precisely, but for this
whole static thing it's just a pain.

IOW, if it actually _worked_ reasonably, I wouldn't care. But clearly it
doesn't. And once it's not working reasonably, it should be fixed.

Linus


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