From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To: Lichao Liu <liulichao@loongson.cn>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>,
Paul Burton <paulburton@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Max Filippov <jcmvbkbc@gmail.com>,
yuanjunqing@loongson.cn, linux-mips@vger.kernel.org
Subject: Re: [PATCH] MIPS: CPU_LOONGSON2EF need software to maintain cache consistency
Date: Tue, 26 May 2020 15:01:28 +0200 [thread overview]
Message-ID: <20200526130128.GA8487@alpha.franken.de> (raw)
In-Reply-To: <e9c015c2-b979-27c8-5f43-7af8d43174c5@loongson.cn>
On Tue, May 26, 2020 at 08:40:28PM +0800, Lichao Liu wrote:
> Loongson-2EF need software maintain cache consistency, So when using
> streaming DMA, software needs to maintain consistency.
>
> dma_map_single() is correct, but dma_unmap_single is wrong.
>
> The function call path:
> 'dma_unmap_single->dma_unmap_page_attrs->dma_direct_unmap_page->
> dma_direct_sync_single_for_cpu->arch_sync_dma_for_cpu->
> cpu_needs_post_dma_flush'
>
> In current version, 'cpu_needs_post_dma_flush' will return false
> at Loongon-2EF platform, and dma_unmap_single will not invalidate cache,
> driver may access wrong dma data.
why should it ? CPU must not touch data while it's mapped for DMA.
> I don't know what's the exact meaning of "fill random cachelines with
> stale data at any time". I always think 'cpu_needs_post_dma_flush()'
> means whether this platform needs software to maintain cache consistency.
this will only happen, if cpu speculates creates dirty cache lines
by speculation as R10k type of CPUs do.
> I found this problem in 4.19.90 kernel's ethernet driver,
> and this patch can fix this problem.
if CPU isn't affected by the R10k speculation problem, it sounds more
like wrong usage of DMA api.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
next prev parent reply other threads:[~2020-05-26 13:07 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 11:14 [PATCH] MIPS: CPU_LOONGSON2EF need software to maintain cache consistency Lichao Liu
2020-05-26 11:38 ` Jiaxun Yang
2020-05-26 12:40 ` Lichao Liu
2020-05-26 13:01 ` Thomas Bogendoerfer [this message]
2020-05-26 13:29 ` Robin Murphy
2020-05-26 15:01 ` Lichao Liu
2020-05-26 15:25 ` Jiaxun Yang
2020-05-26 16:00 ` Thomas Bogendoerfer
2020-05-26 16:42 ` Jiaxun Yang
2020-05-26 16:16 ` Thomas Bogendoerfer
2020-05-26 13:25 ` Jiaxun Yang
2020-05-26 14:50 ` Lichao Liu
2020-05-27 10:49 ` Thomas Bogendoerfer
-- strict thread matches above, loose matches on Subject: below --
2020-05-28 1:10 Lichao Liu
2020-05-28 6:05 ` Jiaxun Yang
2020-05-28 7:44 ` Thomas Bogendoerfer
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