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Mon, 20 Apr 2026 12:49:04 -0700 (PDT) Date: Mon, 20 Apr 2026 12:49:03 -0700 From: Stanislav Fomichev To: Jason Xing Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, bjorn@kernel.org, magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, jonathan.lemon@gmail.com, sdf@fomichev.me, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing Subject: Re: [PATCH net v2 8/8] xsk: fix u64 descriptor address truncation on 32-bit architectures Message-ID: References: <20260420082805.14844-1-kerneljasonxing@gmail.com> <20260420082805.14844-9-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260420082805.14844-9-kerneljasonxing@gmail.com> On 04/20, Jason Xing wrote: > From: Jason Xing > > In copy mode TX, xsk_skb_destructor_set_addr() stores the 64-bit > descriptor address into skb_shinfo(skb)->destructor_arg (void *) via a > uintptr_t cast: > > skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t)addr | 0x1UL); > > On 32-bit architectures uintptr_t is 32 bits, so the upper 32 bits of > the descriptor address are silently dropped. In XDP_ZEROCOPY unaligned > mode the chunk offset is encoded in bits 48-63 of the descriptor > address (XSK_UNALIGNED_BUF_OFFSET_SHIFT = 48), meaning the offset is > lost entirely. The completion queue then returns a truncated address to > userspace, making buffer recycling impossible. > > Fix this by handling the 32-bit case directly in > xsk_skb_destructor_set_addr(): when !CONFIG_64BIT, allocate an xsk_addrs > struct (the same path already used for multi-descriptor SKBs) to store > the full u64 address. Is it easier to make XSK `depends on 64BIT` to avoid dealing with that? Does anybody seriously run af_xdp on 32 bit systems?