On Sun, May 28, 2023 at 10:02:49PM +0200, Jiri Olsa wrote: > On Fri, May 26, 2023 at 07:54:17PM +0100, Greg KH wrote: > > On Mon, May 22, 2023 at 10:33:44PM +0200, Jiri Olsa wrote: > > > hi, > > > we see broken access to user space with bpf_probe_read/bpf_probe_read_str > > > helpers on arm64 with 5.4 kernel. The problem is that both helpers try to > > > read user memory by calling probe_kernel_read, which seems to work on x86 > > > but fails on arm64. > > > > Has this ever worked on arm64 for the 5.4 kernel tree? If not, it's not > > really a regression, and so, why not use a newer kernel that has this > > new feature added to it there? > > > > In other words, what requires you to use the 5.4.y tree and requires > > feature parity across architectures? > > we have a customer running ok on x86 v5.4, but arm64 is broken with > the same bpf/user space code Again why can they not use a newer kernel version? What forces this customer to be stuck with a specific kernel version that spans different processor types? > upgrade is an option of course, but it's not a big change and we can > have 5.4 working on arm64 as well For loads of other reasons, I'd recommend 5.15 or newer for arm64, so why not use that? > I can send out the change that will be closer to upstream changes, > if that's a concern.. with adding the new probe helpers, which I > guess is not a problem, because it does not change current API You are trying to add features to a stable kernel that are not regression fixes, which is something that we generally do not accept into stable kernels. thnaks, greg k-h
