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([2620:10d:c092:600::1:b2ad]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ae6e7e90388sm485231566b.16.2025.07.12.05.15.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 12 Jul 2025 05:15:36 -0700 (PDT) Message-ID: Date: Sat, 12 Jul 2025 13:16:54 +0100 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v9 2/8] netmem: introduce utility APIs to use struct netmem_desc To: Byungchul Park , Mina Almasry Cc: willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, hawk@kernel.org, akpm@linux-foundation.org, davem@davemloft.net, john.fastabend@gmail.com, andrew+netdev@lunn.ch, toke@redhat.com, tariqt@nvidia.com, edumazet@google.com, pabeni@redhat.com, saeedm@nvidia.com, leon@kernel.org, ast@kernel.org, daniel@iogearbox.net, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com, hannes@cmpxchg.org, ziy@nvidia.com, jackmanb@google.com References: <20250710082807.27402-1-byungchul@sk.com> <20250710082807.27402-3-byungchul@sk.com> <20250711010253.GB40145@system.software.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20250711010253.GB40145@system.software.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/11/25 02:02, Byungchul Park wrote: > On Thu, Jul 10, 2025 at 11:11:51AM -0700, Mina Almasry wrote: ...>>> +#define nmdesc_to_page(nmdesc) (_Generic((nmdesc), \ >>> + const struct netmem_desc * : (const struct page *)(nmdesc), \ >>> + struct netmem_desc * : (struct page *)(nmdesc))) >>> + >>> +static inline struct netmem_desc *page_to_nmdesc(struct page *page) >>> +{ >>> + VM_BUG_ON_PAGE(PageTail(page), page); >>> + return (struct netmem_desc *)page; >>> +} >>> + >> >> It's not safe to cast a page to netmem_desc, without first checking if >> it's a pp page or not, otherwise you may be casting random non-pp >> pages to netmem_desc... I'd suggest to rename it to sth like pp_page_to_nmdesc() and add: DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(page)); ... > Agree, but page_to_nmdesc() will be used in page_pool_page_is_pp() to > check if it's a pp page or not: > > static inline bool page_pool_page_is_pp(struct page *page) > { > struct netmem_desc *desc = page_to_nmdesc(page); > > return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > } > > Hm.. maybe, it'd be better to resore the original code and remove this > page_to_nmdesc() helper. FYI, the original code was: > > static inline bool page_pool_page_is_pp(struct page *page) > { > struct netmem_desc *desc = (struct netmem_desc *)page; > > return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > } ... And use this version. It's supposed to be temporary anyway. It'd be great to add a build check that the page still has space to alias with for now. -- Pavel Begunkov