Messages in this thread | | | Date | Tue, 30 Sep 2003 18:26:18 +0100 | From | Dave Jones <> | Subject | Re: [PATCH] Mutilated form of Andi Kleen's AMD prefetch errata patch |
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On Tue, Sep 30, 2003 at 05:54:50PM +0100, Jamie Lokier wrote:
> > > - I don't see anything that prevents a PPro-compiled kernel from booting > > > on a P5MMX with the F00F erratum. > > Compiled with -m686 - Uses CMOV, won't boot. > Ok, not PPro, but with Processor Family set to K6, CYRIXIII, or any of > the 3 WINCHIP choices, it is compiled with -march=i585 and without F00F.
in theory, these should be interchangable. Not tested though.
> (Fixing that by adding F00F too all those non-Intel processors, just to > make sure non-F00F kernels crash with a cmov instruction is too subtle > for my taste.)
this case is a little more obscure imo, and not worth the effort.
> Anyway, it should complain about lack of cmov not crash :)
not easy, given we execute cmov instructions before we even hit a printk. Such a test & output needs to be done in assembly in early startup.
> > 1. The splitting of X86_FEATURE_XMM into X86_FEATURE_XMM_PREFETCH and > > X86_FEATURE_3DNOW_PREFETCH doesn't seem to really buy us anything > > other than complication. > I once suggested turning off XMM entirely when prefetch is broken and > not fixed, but that resulted in a mild toasting, hence the extra > synthetic flag.
Which gets us back to the question of why this is needed at all ? You said earlier "In case you hadn't fully grokked it, my code doesn't disable the workaround!" So why do you need this ?
> > - If we haven't set CONFIG_X86_PREFETCH_FIXUP (say a P4 kernel), this > > code path isn't taken, and we end up not doing prefetches on P4's too > > as you're not setting X86_FEATURE_XMM_PREFETCH anywhere else, and apply_alternatives > > leaves them as NOPs. > > - Newer C3s are 686's with prefetch, this nobbles them too. > Read the code again. It does what you think it doesn't do, so to speak.
Yep, brain fart.
Dave
-- Dave Jones http://www.codemonkey.org.uk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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