linux-kernel - [PATCH] net: don't use kvzalloc for DMA memory

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Date:   Wed, 18 Apr 2018 10:34:26 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
cc:     Joby Poriyath <joby.poriyath@...rix.com>,
        Ben Hutchings <bhutchings@...arflare.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] net: don't use kvzalloc for DMA memory

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@...hat.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;