linux-kernel - Re: [x86, vdso] BUG: unable to handle kernel paging request at d34bd000

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Message-ID: <CA+55aFwuVYds=ssv755WKBvux1ru6fcDLGi+ORSFyU8xYP7+=w@mail.gmail.com>
Date:	Mon, 10 Mar 2014 14:20:34 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Stefani Seibold <stefani@...bold.net>,
	Andy Lutomirski <luto@...capital.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>,
	Martin Runge <Martin.Runge@...de-schwarz.com>
Subject: Re: [x86, vdso] BUG: unable to handle kernel paging request at d34bd000

On Mon, Mar 10, 2014 at 1:19 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> If the only immediate problem is the code generation size, then Andy
> already had a (simpler) hack-around:
>
>   #undef CONFIG_OPTIMIZE_INLINING
>   #undef CONFIG_X86_PPRO_FENCE
>
> in vclock_gettime.c

Btw, we should seriously consider getting rid of CONFIG_X86_PPRO_FENCE.

It was of questionable value to begin with, and I think that the
actual PPro bug is about one of

 - Errata 66, "Delayed line invalidation".
 - Errata 92, "Potential loss of data coherency"

both of which affect all PPro versions afaik (there is also a UP
errata 51 wrt ordering of cached and uncached accesses that was fixed
in the sB1 stepping).

And as far as I know, we have never actually seen the bug in real
life, EVEN WHEN PPRO WAS COMMON. The workaround was always based on
knowledge of the errata afaik.

So I do think we might want to consider retiring that config option
entirely as a "historical oddity".

And very much so for the vdso case. Do we even do the asm alternative
fixups for the vdso?

I also suspect we should get rid of CONFIG_X86_OOSTORE, or at least
limit it to !SMP - I don't think anybody ever made SMP systems with
those IDT/Centaur Winchip chips in them.

                Linus
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