linux-kernel - Re: Why does ion_cma_allocate need GFP_HIGHUSER

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] [day] [month] [year] [list]

Message-ID: <54655D1D.9080109@lge.com>
Date:	Fri, 14 Nov 2014 10:38:37 +0900
From:	Gioh Kim <gioh.kim@....com>
To:	Laura Abbott <lauraa@...eaurora.org>,
	Colin Cross <ccross@...roid.com>,
	Joonsoo Kim <js1304@...il.com>
CC:	John Stultz <john.stultz@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	"이건호/책임연구원/SW Platform(연)AOT팀(gunho.lee@....com)" <gunho.lee@....com>
Subject: Re: Why does ion_cma_allocate need GFP_HIGHUSER | __GFP_ZERO flags?



2014-11-14 오전 10:24에 Laura Abbott 이(가) 쓴 글:
> On 11/12/2014 11:18 PM, Gioh Kim wrote:
>> Hi,
>>
>> I'm wondering why dma_alloc_coherent needs GFP_HIGHUSER | __GFP_ZERO flags in ion_cma_allocate().
>>
>> I think dma_alloc_coherent can go to __dma_alloc if the system has CMA area.
>> If __GFP_WAIT flag is set, it allocates memory from atomic pool.
>> So I think calling dma_alloc_coherent with __GFP_WAIT is enough.
>>
>> And can I get zero-filled-memory from CMA if I set __GFP_ZERO?
>>
>>
> 
> If we are actually using CMA, the GFP flags don't make much of a difference. If
> we didn't have CMA, using GFP_HIGHUSER would still be appropriate. The memory
> is going to userspace so the user part is necessary and there should be no need
> for a lowmem mapping so highmem can be used. __GFP_ZERO might be redundant since
> the dma layer zeros memory anyway but it's probably safe.

If cma-heap can be created even-if the system doesn't have CMA area, you're right.

But I think cma-heap should be created only if the system has CMA area.
I think, in no CMA system, cma-heap creation and/or allocation from cma-heap should be failed,
not allocate memory from lowmem or highmem as you say.

Thanks for your reply.

> 
> I think the flags should be fine as is.
> 
> Thanks,
> Laura
> 
--
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/