linux-kernel - Re: [Linaro-mm-sig] [PATCH v3] staging: android: ion: Zero CMA allocated memory

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Date:   Sat, 27 Jan 2018 10:04:01 +0800
From:   Chen Feng <puck.chen@...ilicon.com>
To:     Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        "Sumit Semwal" <sumit.semwal@...aro.org>
CC:     <devel@...verdev.osuosl.org>, Greg KH <gregkh@...uxfoundation.org>,
        <linaro-mm-sig@...ts.linaro.org>, <linux-kernel@...r.kernel.org>,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Xiaqing (A)" <saberlily.xia@...ilicon.com>,
        Zhuangluan Su <suzhuangluan@...ilicon.com>
Subject: Re: [Linaro-mm-sig] [PATCH v3] staging: android: ion: Zero CMA
 allocated memory



On 2018/1/27 1:48, Liam Mark wrote:
> Since commit 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
> the CMA API is now used directly and therefore the allocated memory is no
> longer automatically zeroed.
> 
> Explicitly zero CMA allocated memory to ensure that no data is exposed to
> userspace.
> 
> Fixes: 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
> Signed-off-by: Liam Mark <lmark@...eaurora.org>
> ---
> Changes in v2:
>   - Clean up the commit message.
>   - Add 'Fixes:'
> 
> Changes in v3:
>  - Add support for highmem pages
> 
>  drivers/staging/android/ion/ion_cma_heap.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/staging/android/ion/ion_cma_heap.c b/drivers/staging/android/ion/ion_cma_heap.c
> index 86196ffd2faf..fa3e4b7e0c9f 100644
> --- a/drivers/staging/android/ion/ion_cma_heap.c
> +++ b/drivers/staging/android/ion/ion_cma_heap.c
> @@ -21,6 +21,7 @@
>  #include <linux/err.h>
>  #include <linux/cma.h>
>  #include <linux/scatterlist.h>
> +#include <linux/highmem.h>
>  
>  #include "ion.h"
>  
> @@ -51,6 +52,22 @@ static int ion_cma_allocate(struct ion_heap *heap, struct ion_buffer *buffer,
>  	if (!pages)
>  		return -ENOMEM;
>  
> +	if (PageHighMem(pages)) {
> +		unsigned long nr_clear_pages = nr_pages;
> +		struct page *page = pages;
> +
> +		while (nr_clear_pages > 0) {
> +			void *vaddr = kmap_atomic(page);
> +
> +			memset(vaddr, 0, PAGE_SIZE);
> +			kunmap_atomic(vaddr);

Here. This way may cause performance latency at mapping-memset-umap page one bye one.

Take a look at ion_heap_pages_zero.

Not very critical, arm64 always have linear mapping.


> +			page++;
> +			nr_clear_pages--;
> +		}
> +	} else {
> +		memset(page_address(pages), 0, size);
> +	}
> +
>  	table = kmalloc(sizeof(*table), GFP_KERNEL);
>  	if (!table)
>  		goto err;
>