On Tue, 2024-02-20 at 10:06 +0100, Daniel Borkmann wrote: > On 2/15/24 2:26 PM, Toke Høiland-Jørgensen wrote: > > The BPF_TEST_RUN code in XDP live frame mode creates a new page pool > > each time it is called and uses that to allocate the frames used for the > > XDP run. This works well if the syscall is used with a high repetitions > > number, as it allows for efficient page recycling. However, if used with > > a small number of repetitions, the overhead of creating and tearing down > > the page pool is significant, and can even lead to system stalls if the > > syscall is called in a tight loop. > > > > Now that we have a persistent system page pool instance, it becomes > > pretty straight forward to change the test_run code to use it. The only > > wrinkle is that we can no longer rely on a custom page init callback > > from page_pool itself; instead, we change the test_run code to write a > > random cookie value to the beginning of the page as an indicator that > > the page has been initialised and can be re-used without copying the > > initial data again. > > > > Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > > [...] > > - > > /* We create a 'fake' RXQ referencing the original dev, but with an > > * xdp_mem_info pointing to our page_pool > > */ > > xdp_rxq_info_reg(&xdp->rxq, orig_ctx->rxq->dev, 0, 0); > > - xdp->rxq.mem.type = MEM_TYPE_PAGE_POOL; > > - xdp->rxq.mem.id = pp->xdp_mem_id; > > + xdp->rxq.mem.type = MEM_TYPE_PAGE_POOL; /* mem id is set per-frame below */ > > xdp->dev = orig_ctx->rxq->dev; > > xdp->orig_ctx = orig_ctx; > > > > + /* We need a random cookie for each run as pages can stick around > > + * between runs in the system page pool > > + */ > > + get_random_bytes(&xdp->cookie, sizeof(xdp->cookie)); > > + > > So the assumption is that there is only a tiny chance of collisions with > users outside of xdp test_run. If they do collide however, you'd leak data. Good point. @Toke: what is the worst-case thing that could happen in case a page is recycled from another pool's user? could we possibly end-up matching the cookie for a page containing 'random' orig_ctx/ctx, so that bpf program later tries to access equally random ptrs? Thanks! Paolo
