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

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Date:	Mon, 10 Mar 2014 16:02:32 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stefani Seibold <stefani@...bold.net>
CC:	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 03/10/2014 02:39 PM, Linus Torvalds wrote:
> On Mon, Mar 10, 2014 at 2:25 PM,  <stefani@...bold.net> wrote:
>>
>> This was discovered by me.
> 
> Sorry for the misattribution.
> 
>> But this is not a real solution, at least when vcpu function support
>> will be added, then the code size will exceed the page size. Reserving
>> two pages for the VDSO is a good option.
> 
> Quite frankly, there is no way in hell I will take a patch like that
> for 3.14 any more, and I would argue against it for stable.
> 
> Now, if this problem never happens with current kernels (because it's
> purely due to the patch in -tip), then I don't much care.
> 

It is only for tip:x86/vdso, so current kernels don't matter.

There is going to be 32-bit use in the embedded sector for a long time
to come, I suspect/fear, so I'm not opposed to giving it a bit of a
performance boost as long as it isn't too invasive.

I think Andy's commentary applies, though :)

> IMO this is dumb.  I can think of two sensible solutions:
> 
> 1. Get rid of compat vdso and replace it with no vdso at all.  This is
> compatible with everything and requires almost no code 
> 
> 2. Fix compat vdso.  Give it as much space as needed, make the address
> dynamic, and relocate it to the right place.


	-hpa

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