On Wed, 18 Apr 2018, Eric Dumazet wrote:> > > 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 at 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.The structure net_device is followed by arbitrary driver-specific data (accessible with the function netdev_priv). And for virtio-net, these driver-specific data must be in DMA memory. Mikulas
On 04/18/2018 09:44 AM, Mikulas Patocka wrote:> > > On Wed, 18 Apr 2018, Eric Dumazet wrote: > >> >> >> 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 at 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. > > The structure net_device is followed by arbitrary driver-specific data > (accessible with the function netdev_priv). And for virtio-net, these > driver-specific data must be in DMA memory.I get that, but how is the original xenvif problem will be solved ? Your patch would add a bug in some other driver(s) I suggest that virtio_net clearly identifies which part needs a specific allocation and does its itself, instead of abusing the netdev_priv storage. Ie use a pointer to a block of memory, allocated by virtio_net, for virtio_net.
From: Mikulas Patocka <mpatocka at redhat.com> Date: Wed, 18 Apr 2018 12:44:25 -0400 (EDT)> The structure net_device is followed by arbitrary driver-specific data > (accessible with the function netdev_priv). And for virtio-net, these > driver-specific data must be in DMA memory.And we are saying that this assumption is wrong and needs to be corrected.
From: Eric Dumazet <eric.dumazet at gmail.com> Date: Wed, 18 Apr 2018 09:51:25 -0700> I suggest that virtio_net clearly identifies which part needs a specific allocation > and does its itself, instead of abusing the netdev_priv storage. > > Ie use a pointer to a block of memory, allocated by virtio_net, for virtio_net.+1
On Wed, 18 Apr 2018, Eric Dumazet wrote:> > > On 04/18/2018 09:44 AM, Mikulas Patocka wrote: > > > > > > On Wed, 18 Apr 2018, Eric Dumazet wrote: > > > >> > >> > >> 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 at 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. > > > > The structure net_device is followed by arbitrary driver-specific data > > (accessible with the function netdev_priv). And for virtio-net, these > > driver-specific data must be in DMA memory. > > I get that, but how is the original xenvif problem will be solved ? > > Your patch would add a bug in some other driver(s) > > I suggest that virtio_net clearly identifies which part needs a specific allocation > and does its itself, instead of abusing the netdev_priv storage. > > Ie use a pointer to a block of memory, allocated by virtio_net, for virtio_net.There are drivers that need to do DMA to driver-specific area. And there are drivers that need driver-specific area larger than kmalloc limit. These are conflicting requirements and one of those drivers must be changed. I suggest to change the drivers that need large driver-specific area. That's why I added the WARN_ON, so that they can be identified. Mikulas
On Wed, 18 Apr 2018, David Miller wrote:> From: Mikulas Patocka <mpatocka at redhat.com> > Date: Wed, 18 Apr 2018 12:44:25 -0400 (EDT) > > > The structure net_device is followed by arbitrary driver-specific data > > (accessible with the function netdev_priv). And for virtio-net, these > > driver-specific data must be in DMA memory. > > And we are saying that this assumption is wrong and needs to be > corrected.So, try to find all the networking drivers that to DMA to the private area. The problem here is that kvzalloc usually returns DMA-able area, but it may return non-DMA area rarely, if the memory is too fragmented. So, we are in a situation, where some networking drivers will randomly fail. Go and find them. Mikulas
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