linux-kernel - Re: [PATCH] CHROMIUM: iommu: rockchip: Make sure that page table state is coherent

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Date:	Tue, 10 Feb 2015 23:21:55 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	Tomasz Figa <tfiga@...omium.org>
Cc:	iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-rockchip@...ts.infradead.org, Joerg Roedel <joro@...tes.org>,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: Re: [PATCH] CHROMIUM: iommu: rockchip: Make sure that page table state is coherent

Am Montag, 9. Februar 2015, 20:19:21 schrieb Tomasz Figa:
> Even though the code uses the dt_lock spin lock to serialize mapping
> operation from different threads, it does not protect from IOMMU
> accesses that might be already taking place and thus altering state
> of the IOTLB. This means that current mapping code which first zaps
> the page table and only then updates it with new mapping which is
> prone to mentioned race.
> 
> In addition, current code assumes that mappings are always > 4 MiB
> (which translates to 1024 PTEs) and so they would always occupy
> entire page tables. This is not true for mappings created by V4L2
> Videobuf2 DMA contig allocator.
> 
> This patch changes the mapping code to always zap the page table
> after it is updated, which avoids the aforementioned race and also
> zap the last page of the mapping to make sure that stale data is
> not cached from an already existing mapping.
> 
> Signed-off-by: Tomasz Figa <tfiga@...omium.org>
> Reviewed-by: Daniel Kurtz <djkurtz@...omium.org>

I don't know enough about iommu-magic yet to review this properly, but on my 
rk3288-firefly the whole display pipeline stays in working condition, down to 
x11 and es2gears, so

Tested-by: Heiko Stuebner <heiko@...ech.de>
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