netdev - Re: [PATCH net-next V2 08/11] net/mlx5e: Convert over to netmem

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Message-ID: <CAHS8izNgY3APhLZWjYwEWyq3g=JiCBWFUcnY4nrXpntnp8zKhw@mail.gmail.com>
Date: Fri, 23 May 2025 10:58:23 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Saeed Mahameed <saeed@...nel.org>
Cc: Tariq Toukan <tariqt@...dia.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Saeed Mahameed <saeedm@...dia.com>, 
	Leon Romanovsky <leon@...nel.org>, Richard Cochran <richardcochran@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, 
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Moshe Shemesh <moshe@...dia.com>, Mark Bloch <mbloch@...dia.com>, Gal Pressman <gal@...dia.com>, 
	Cosmin Ratiu <cratiu@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>
Subject: Re: [PATCH net-next V2 08/11] net/mlx5e: Convert over to netmem

On Thu, May 22, 2025 at 4:54 PM Saeed Mahameed <saeed@...nel.org> wrote:
> >>  static inline void
> >>  mlx5e_copy_skb_header(struct mlx5e_rq *rq, struct sk_buff *skb,
> >> -                     struct page *page, dma_addr_t addr,
> >> +                     netmem_ref netmem, dma_addr_t addr,
> >>                       int offset_from, int dma_offset, u32 headlen)
> >>  {
> >> -       const void *from = page_address(page) + offset_from;
> >> +       const void *from = netmem_address(netmem) + offset_from;
> >
> >I think this needs a check that netmem_address != NULL and safe error
> >handling in case it is? If the netmem is unreadable, netmem_address
> >will return NULL, and because you add offset_from to it, you can't
> >NULL check from as well.
> >
>
> Nope, this code path is not for GRO_HW, it is always safe to assume this is
> not iov_netmem.
>

OK, thanks for checking. It may be worth it to add
DEBUG_NET_WARN_ON_ONCE(netmem_address(netmem)); in these places where
you're assuming the netmem is readable and has a valid address. It
would be a very subtle bug later on if someone moves the code or
something and suddenly you have unreadable netmem being funnelled
through these code paths. But up to you.

-- 
Thanks,
Mina