linux-kernel - Re: [PATCH] ARM: dma-mapping: always clear allocated buffers in __alloc_from

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Date:   Wed, 13 Mar 2019 19:29:00 +0100
From:   Christoph Hellwig <hch@....de>
To:     Yue Haibing <yuehaibing@...wei.com>
Cc:     linux@...linux.org.uk, akpm@...ux-foundation.org,
        robin.murphy@....com, iamjoonsoo.kim@....com, hch@....de,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: dma-mapping: always clear allocated buffers in
 __alloc_from_pool

On Tue, Mar 12, 2019 at 05:16:37PM +0800, Yue Haibing wrote:
> From: YueHaibing <yuehaibing@...wei.com>
> 
> Like commit 518a2f1925c3 ("dma-mapping: zero memory returned
> from dma_alloc_*"), if we want to map memory from the DMA
> allocator to userspace it must be zeroed at allocation time 
> to prevent stale data leaks. On arm platform, if the allocator
> is pool_allocator in __dma_alloc, then the mem is alloced by
> __alloc_from_pool, which also need be zeroed.

The observations looks correct, and because this memory is already
remapped I don't think we need __dma_clear_buffer here.

But I'd love to see a review from Russell as well.