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SubjectRe: [PATCH] net: don't use kvzalloc for DMA memory
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On 04/18/2018 07:34 AM, Mikulas Patocka wrote:
> The patch 74d332c13b21 changes alloc_netdev_mqs to use vzalloc if kzalloc
> fails (later patches change it to kvzalloc).
>
> The problem with this is that if the vzalloc function is actually used,
> virtio_net doesn't work (because it expects that the extra memory should
> be accessible with DMA-API and memory allocated with vzalloc isn't).
>
> This patch changes it back to kzalloc and adds a warning if the allocated
> size is too large (the allocation is unreliable in this case).
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Fixes: 74d332c13b21 ("net: extend net_device allocation to vmalloc()")
>
> ---
> net/core/dev.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/net/core/dev.c
> ===================================================================
> --- linux-2.6.orig/net/core/dev.c 2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/net/core/dev.c 2018-04-18 16:24:43.000000000 +0200
> @@ -8366,7 +8366,8 @@ struct net_device *alloc_netdev_mqs(int
> /* ensure 32-byte alignment of whole construct */
> alloc_size += NETDEV_ALIGN - 1;
>
> - p = kvzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> + WARN_ON(alloc_size > PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER);
> + p = kzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
> if (!p)
> return NULL;
>
>

Since when a net_device needs to be in DMA zone ???

I would rather fix virtio_net, this looks very suspect to me.

Each virtio_net should probably allocate the exact amount of DMA-memory it wants,
instead of expecting core networking stack to have a huge chunk of DMA-memory for everything.

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