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Message-ID: <CANn89iJSUg8LJkpRrT0BWWMTiHixJVo1hSpt2-2kBw7BzB8Mqg@mail.gmail.com>
Date: Tue, 9 Jul 2024 08:27:45 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Breno Leitao <leitao@...ian.org>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Kees Cook <kees@...nel.org>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>, keescook@...omium.org, horms@...nel.org,
nex.sw.ncis.osdt.itp.upstreaming@...el.com, linux-hardening@...r.kernel.org,
Alexander Lobakin <aleksander.lobakin@...el.com>,
Przemek Kitszel <przemyslaw.kitszel@...el.com>, Jiri Pirko <jiri@...nulli.us>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Daniel Borkmann <daniel@...earbox.net>,
Lorenzo Bianconi <lorenzo@...nel.org>, Johannes Berg <johannes.berg@...el.com>,
Heiner Kallweit <hkallweit1@...il.com>,
"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] netdevice: define and allocate &net_device _properly_
On Tue, Jul 9, 2024 at 5:54 AM Breno Leitao <leitao@...ian.org> wrote:
>
> From: Alexander Lobakin <aleksander.lobakin@...el.com>
>
> In fact, this structure contains a flexible array at the end, but
> historically its size, alignment etc., is calculated manually.
> There are several instances of the structure embedded into other
> structures, but also there's ongoing effort to remove them and we
> could in the meantime declare &net_device properly.
> Declare the array explicitly, use struct_size() and store the array
> size inside the structure, so that __counted_by() can be applied.
> Don't use PTR_ALIGN(), as SLUB itself tries its best to ensure the
> allocated buffer is aligned to what the user expects.
> Also, change its alignment from %NETDEV_ALIGN to the cacheline size
> as per several suggestions on the netdev ML.
>
> bloat-o-meter for vmlinux:
>
> free_netdev 445 440 -5
> netdev_freemem 24 - -24
> alloc_netdev_mqs 1481 1450 -31
>
> On x86_64 with several NICs of different vendors, I was never able to
> get a &net_device pointer not aligned to the cacheline size after the
> change.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
> ---
> Changelog:
>
> v2:
> * Rebased Alexander's patch on top of f750dfe825b90 ("ethtool: provide
> customized dim profile management").
> * Removed the ALIGN() of SMP_CACHE_BYTES for sizeof_priv.
>
> v1:
> * https://lore.kernel.org/netdev/90fd7cd7-72dc-4df6-88ec-fbc8b64735ad@intel.com
>
> include/linux/netdevice.h | 12 +++++++-----
> net/core/dev.c | 30 ++++++------------------------
> net/core/net-sysfs.c | 2 +-
> 3 files changed, 14 insertions(+), 30 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 93558645c6d0..f0dd499244d4 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2199,10 +2199,10 @@ struct net_device {
> unsigned short neigh_priv_len;
> unsigned short dev_id;
> unsigned short dev_port;
> - unsigned short padded;
> + int irq;
> + u32 priv_len;
>
> spinlock_t addr_list_lock;
> - int irq;
>
> struct netdev_hw_addr_list uc;
> struct netdev_hw_addr_list mc;
> @@ -2406,7 +2406,10 @@ struct net_device {
>
> /** @irq_moder: dim parameters used if IS_ENABLED(CONFIG_DIMLIB). */
> struct dim_irq_moder *irq_moder;
> -};
> +
> + u8 priv[] ____cacheline_aligned
> + __counted_by(priv_len);
> +} ____cacheline_aligned;
> #define to_net_dev(d) container_of(d, struct net_device, dev)
>
> /*
> @@ -2596,7 +2599,7 @@ void dev_net_set(struct net_device *dev, struct net *net)
> */
> static inline void *netdev_priv(const struct net_device *dev)
> {
> - return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
> + return (void *)dev->priv;
Minor remark : the cast is not needed, but this is fine.
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
It would be great to get rid of NETDEV_ALIGN eventually.
Thanks.
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