linux-kernel - Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if RISCV_DMA

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]

Message-ID: <7bc138f7-d5e9-471a-ae82-d6c490645623@flygoat.com>
Date: Fri, 22 Dec 2023 15:45:34 +0000
From: Jiaxun Yang <jiaxun.yang@...goat.com>
To: Maxim Kochetkov <fido_max@...ox.ru>, Conor Dooley <conor@...nel.org>
Cc: Christoph Hellwig <hch@....de>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, robh@...nel.org, mpe@...erman.id.au,
 aou@...s.berkeley.edu, palmer@...belt.com, paul.walmsley@...ive.com
Subject: Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if
 RISCV_DMA_NONCOHERENT is not set



在 2023/12/22 15:38, Maxim Kochetkov 写道:
>
>
> On 22.12.2023 17:54, Conor Dooley wrote:
>
>>> etc..) do not have this feature. These devices will use value from
>>> device_initialize(). And we have no possibility to change
>>> dma_default_coherent value by disabling ARCH_DMA_DEFAULT_COHERENT.
>>> Moreover, changing dma_default_coherent from false to true may cause
>>> regression for other devices.
>>
>> How can there be a regression when dma has been coherent by default for
>> the RISC-V kernel from day 1?
>
> Before ARCH_DMA_DEFAULT_COHERENT patch dma_default_coherent was used 
> unassigned as "false" in device_initialize():
> ..........
> #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
>     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
>     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
>     dev->dma_coherent = dma_default_coherent;
> #endif
> ..........
> And now it becomes "true". It may change behavior of other non-DT 
> drivers.
I don't see any problem here, default is default.
Actually leaving those device with  dev->dma_coherent = false is risky, 
because
we can't guarantee underlying cache flush functions are here.

If a non-dt device do need to override it, it should be done in 
arch_setup_dma_ops.

Thanks
- Jiaxun