> On Sep 28, 2022, at 2:42 AM, Jesper Dangaard Brouer <jbrouer@xxxxxxxxxx> wrote: > > > On 26/09/2022 20.47, Song Liu wrote: >> Changes v1 => v2: >> 1. Update arch_prepare_bpf_dispatcher to use a RO image and a RW buffer. >> (Alexei) Note: I haven't found an existing test to cover this part, so >> this part was tested manually (comparing the generated dispatcher is >> the same). >> Jeff Layton reported CPA W^X warning linux-next [1]. It turns out to be >> W^X issue with bpf trampoline and bpf dispatcher. Fix these by: >> 1. Use bpf_prog_pack for bpf_dispatcher; >> 2. Set memory permission properly with bpf trampoline. > > Indirectly related to your patchset[0]. > - TL;DR calling set_memory_x() have side-effects > > We are getting reports that loading BPF-progs (jit stage) cause issues for RT in the form of triggering work on isolated CPUs. It looks like BTF JIT stage cause a TLB flush on all CPUs, including isolated CPUs. > > The triggering function is set_memory_x() (see call-stack[2]). > > We have noticed (and appreciate) you have previously improved the situation in this patchset[3]: > [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=80123f0ac4a6 > > Is this patchset also part of improving the situation, or does it introduce more calls to set_memory_x() ? This set doesn't change numbers of set_memory_x() calls for trampolines. We plan to move trampolines to use bpf_prog_pack (or the new vmalloc_exec, if I am lucky) in 6.2. We will see fewer set_memory_x() calls after that. Thanks, Song > > >> [1] https://lore.kernel.org/lkml/c84cc27c1a5031a003039748c3c099732a718aec.camel@xxxxxxxxxx/ > > > [2] Call stack triggering issue: > > smp_call_function_many_cond+0x1 > smp_call_function+0x39 > on_each_cpu+0x2a > cpa_flush+0x11a > change_page_attr_set_clr+0x129 > set_memory_x+0x37 > bpf_int_jit_compile+0x36f > bpf_prog_select_runtime+0xc6 > bpf_prepare_filter+0x523 > sk_attach_filter+0x13 > sock_setsockopt+0x920 > __sys_setsockopt+0x16a > __x64_sys_setsockopt+0x20 > do_syscall_64+0x87 > entry_SYSCALL_64_after_hwframe+0x65 > > > [0] https://lore.kernel.org/all/20220926184739.3512547-1-song@xxxxxxxxxx/#r > > --Jesper >
