linux-kernel - Re: [PATCH v4 0/2] mm/highmem: make kmap cache coloring aware

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Date:	Tue, 26 Aug 2014 10:45:47 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Joshua Kinard <kumba@...too.org>
CC:	Ralf Baechle <ralf@...ux-mips.org>,
	Max Filippov <jcmvbkbc@...il.com>,
	linux-xtensa@...ux-xtensa.org, Chris Zankel <chris@...kel.net>,
	Marc Gauthier <marc@...ence.com>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	Steven Hill <Steven.Hill@...tec.com>
Subject: Re: [PATCH v4 0/2] mm/highmem: make kmap cache coloring aware

On 08/25/2014 07:41 PM, Joshua Kinard wrote:
> On 08/25/2014 20:36, David Daney wrote:
>> On 08/25/2014 04:55 PM, Joshua Kinard wrote:
>>> On 08/25/2014 13:16, Ralf Baechle wrote:
>>>> On Sat, Aug 02, 2014 at 05:11:37AM +0400, Max Filippov wrote:
>>>>
>>>>> this series adds mapping color control to the generic kmap code, allowing
>>>>> architectures with aliasing VIPT cache to use high memory. There's also
>>>>> use example of this new interface by xtensa.
>>>>
>>>> I haven't actually ported this to MIPS but it certainly appears to be
>>>> the right framework to get highmem aliases handled on MIPS, too.
>>>>
>>>> Though I still consider increasing PAGE_SIZE to 16k the preferable
>>>> solution because it will entirly do away with cache aliases.
>>>
>>> Won't setting PAGE_SIZE to 16k break some existing userlands (o32)?  I use a
>>> 4k PAGE_SIZE because the last few times I've tried 16k or 64k, init won't
>>> load (SIGSEGVs or such, which panicks the kernel).
>>>
>>
>> It isn't supposed to break things.  Using "stock" toolchains should result
>> in executables that will run with any page size.
>>
>> In the past, some geniuses came up with some linker (ld) patches that, in
>> order to save a few KB of RAM, produced executables that ran only on 4K pages.
>>
>> There were some equally astute Debian emacs package maintainers that were
>> carrying emacs patches into Debian that would not work on non-4K page size
>> systems.
>>
>> That said, I think such thinking should be punished.  The punishment should
>> be to not have their software run when we select non-4K page sizes.  The
>> vast majority of prepackaged software runs just fine with a larger page size.
>
> Well, it does appear to mostly work now w/ 16k PAGE_SIZE.  The Octane booted
> into userland with just a couple of "illegal instruction" errors from 'rm'
> and 'mdadm'.  I wonder if that's tied to a hardcoded PAGE_SIZE somewhere.
> Have to dig around and find something that reproduces the problem on demand.
>

What does the output of "readelf -lW" look like for the failing 
programs?  If the "Offset" and "VirtAddr" constraints for the LOAD 
Program Headers are not possible to achieve with the selected PAGE_SIZE, 
you will see problems.  A "correct" toolchain will generate binaries 
that work with any PAGE_SIZE up to 64K.

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