From: Ralf Baechle <ralf@linux-mips.org>
To: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: linux-mips@linux-mips.org
Subject: Re: VMALLOC_END, TASK_SIZE and FIXADDR_START for 64 bit MIPS kernels
Date: Mon, 8 Feb 2010 15:02:14 +0100 [thread overview]
Message-ID: <20100208140213.GB11334@linux-mips.org> (raw)
In-Reply-To: <20100203222250.GA21139@ericsson.com>
On Wed, Feb 03, 2010 at 02:22:50PM -0800, Guenter Roeck wrote:
> since it came up during the review of the patch for virtual memory detection
> on 64 bit mips kernels, I looked further into making vmalloc_end
> a variable and TASK_SIZE dependent on the virtual memory size.
>
> That turned out to be relatively straightforward, and I have a working patch.
>
> The one question I still have is about FIXADDR_START. It is currently
> set to one of 0xff000000, 0xfffe0000, or (0xff000000 - 0x20000),
> depending on the target CPU.
>
> Quoting from one of the comments during the review,
> " ... ensure the value of vmalloc_end is <= FIXADDR_START".
>
> Obviously that is currently not the case. Is that a concern, or is it good as it is ?
Now with allocations potencially happening top-down this is potencially a
serious problem. Details would depend on details of platform, processor and
kernel configuration.
I said vmalloc_end is <= FIXADDR_START" but more accurately we simply
need to avoid a conflict between the different virtual address space users.
Some CPUs have fixed mappings in their hardware in the KSEG2/KSEG3 range;
those mappings can't be overriden by a TLB mapping. To deal with that
sort of architectural candy I think a call into the address space allocator
for kernel virtual memory is probably nicest thing but something simplier
than that would probable have to do for 2.6.34.
Ralf
prev parent reply other threads:[~2010-02-08 14:01 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-03 22:22 VMALLOC_END, TASK_SIZE and FIXADDR_START for 64 bit MIPS kernels Guenter Roeck
2010-02-08 14:02 ` Ralf Baechle [this message]
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