linux-kernel - Re: [patch 02/41] cpu alloc: The allocator

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 04 Jun 2008 08:30:23 -0700
From:	Mike Travis <travis@....com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Christoph Lameter <clameter@....com>,
	Eric Dumazet <dada1@...mosbay.com>, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch 02/41] cpu alloc: The allocator

Rusty Russell wrote:
> On Friday 30 May 2008 15:20:45 Christoph Lameter wrote:
>> On Fri, 30 May 2008, Eric Dumazet wrote:
>>>> +static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]);
>>> area[] is not guaranteed to be aligned on anything but 4 bytes.
>>>
>>> If someone then needs to call cpu_alloc(8, GFP_KERNEL, 8), it might get
>>> an non aligned result.
>>>
>>> Either you should add an __attribute__((__aligned__(PAGE_SIZE))),
>>> or take into account the real address of area[] in cpu_alloc() to avoid
>>> waste of up to PAGE_SIZE bytes
>>> per cpu.
>> I think cacheline aligning should be sufficient. People should not
>> allocate large page aligned objects here.
> 
> I vaguely recall there were issues with this in the module code.  They might 
> be gone now, but failing to meet alignment contraints without a big warning 
> would suck.
> 
> But modifying your code to consider the actual alignment is actually pretty 
> trivial, AFAICT.
> 
> Cheers,
> Rusty.

So paraphrasing my earlier email, we should add:

	bitmap_find_free_area(bitmap, nbits, size, align, alignbase)

so that > cacheline alignment is possible?

My thinking is that if we do go to true dynamically sized cpu_alloc area then
allocating PAGE_SIZE units may be both practical and worthwhile...?

Thanks,
Mike
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/