Re: 3.2-rc2 freezes on boot for AMD K6 - bisected to commit bcb80e53877c2045d9e52f4a71372c3fe6501f6f

From: Larry Finger
Date: Sat Dec 03 2011 - 22:15:28 EST


On 12/03/2011 05:07 PM, Linus Torvalds wrote:
On Sat, Dec 3, 2011 at 12:43 PM, Larry Finger<Larry.Finger@xxxxxxxxxxxx> wrote:

Ugh. I hate that patch.

It's completely stupid. If "rdmsr_safe()" doesn't work at that point
in the boot, then it's pointless to call it.

So this change is pure and utter crap:

- rdmsr_safe(MSR_AMD64_PATCH_LEVEL,&c->microcode,&dummy);
+ if (c->x86>= 0xf)
+ rdmsr_safe(MSR_AMD64_PATCH_LEVEL,&c->microcode,&dummy);

because it is misleading as hell: that rdmsr isn't *safe* at all, so
why are we calling "rdmsr_safe()"?

It's wrong.

The right patch would either just remove the "safe" part (and just say
that the register has to be supported if c->x86>= 0xf), but quite
honestly, I don't see why we do that thing in early_init_amd() AT ALL.
Afaik, the microcode version field isn't really *needed* by the
kernelin the first place, much less is it needed by the *early* boot,
so why isn't this in 'init_amd()' a bit later when the "safe" version
actually *works*?

IOW, I think the patch should be something like the attached (TOTALLY
UNTESTED) patch. Larry, does this work for you? It just moves the
rdmsr_safe() to the later function.

Borislav?

I just updated mainline to 3.2-rc4, and that patch is not included. Please
check with Ingo to see why it was not available. It is a real show stopper
for old AMD CPUs.

Ingo seems to have fallen off the earth for the last two weeks.
There's *one* email form him about 12 hours ago, before that the last
one I see is from early November.

Ingo, everything ok?

Linus

Linus,

With your patch, my K8 box boots fine running 3.2-rc4. If you wish, you may add a "Tested-by: Larry Finger <Larry.Finger@xxxxxxxxxxxx>.

Thanks for the explanation, and the patch,

Larry
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