Re: [PATCH net v2 8/8] xsk: fix u64 descriptor address truncation on 32-bit architectures

[Stanislav Fomichev <sdf.kernel@gmail.com>]

On 04/20, Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent.com>
> 
> 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?