netdev - Re: [PATCH net-next v3 2/3] net: introduce abstraction for network memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHS8izOp_m9SyPjNth-iYBXH2qQQpc9PuZaHbpUL=H0W=CVHgQ@mail.gmail.com>
Date: Thu, 21 Dec 2023 15:44:22 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Shakeel Butt <shakeelb@...gle.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux.dev, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella <sgarzare@...hat.com>, 
	David Howells <dhowells@...hat.com>, Jason Gunthorpe <jgg@...dia.com>, 
	Christian König <christian.koenig@....com>, 
	Yunsheng Lin <linyunsheng@...wei.com>, Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next v3 2/3] net: introduce abstraction for network memory

On Thu, Dec 21, 2023 at 3:23 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Wed, Dec 20, 2023 at 01:45:01PM -0800, Mina Almasry wrote:
> > Add the netmem_ref type, an abstraction for network memory.
> >
> > To add support for new memory types to the net stack, we must first
> > abstract the current memory type. Currently parts of the net stack
> > use struct page directly:
> >
> > - page_pool
> > - drivers
> > - skb_frag_t
> >
> > Originally the plan was to reuse struct page* for the new memory types,
> > and to set the LSB on the page* to indicate it's not really a page.
> > However, for compiler type checking we need to introduce a new type.
> >
> > netmem_ref is introduced to abstract the underlying memory type. Currently
> > it's a no-op abstraction that is always a struct page underneath. In
> > parallel there is an undergoing effort to add support for devmem to the
> > net stack:
> >
> > https://lore.kernel.org/netdev/20231208005250.2910004-1-almasrymina@google.com/
> >
> > Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> >
> > ---
> >
> > v3:
> >
> > - Modify struct netmem from a union of struct page + new types to an opaque
> >   netmem_ref type.  I went with:
> >
> >   +typedef void *__bitwise netmem_ref;
> >
> >   rather than this that Jakub recommended:
> >
> >   +typedef unsigned long __bitwise netmem_ref;
> >
> >   Because with the latter the compiler issues warnings to cast NULL to
> >   netmem_ref. I hope that's ok.
> >
>
> Can you share what the warning was? You might just need __force
> attribute. However you might need this __force a lot. I wonder if you
> can just follow struct encoded_page example verbatim here.
>

The warning is like so:

./include/net/page_pool/helpers.h: In function ‘page_pool_alloc’:
./include/linux/stddef.h:8:14: warning: returning ‘void *’ from a
function with return type ‘netmem_ref’ {aka ‘long unsigned int’} makes
integer from pointer without a cast [-Wint-conversion]
    8 | #define NULL ((void *)0)
      |              ^
./include/net/page_pool/helpers.h:132:24: note: in expansion of macro
‘NULL’
  132 |                 return NULL;
      |                        ^~~~

And happens in all the code where:

netmem_ref func()
{
    return NULL;
}

It's fixable by changing the return to `return (netmem_ref NULL);` or
`return 0;`, but I feel like netmem_ref should be some type which
allows a cast from NULL implicitly.

Also as you (and patchwork) noticed, __bitwise should not be used with
void*; it's only meant for integer types. Sorry I missed that in the
docs and was not running make C=2.

-- 
Thanks,
Mina