On Tue Mar 26, 2024 at 6:15 PM EET, Calvin Owens wrote: > On Wednesday 03/27 at 00:24 +0900, Masami Hiramatsu wrote: > > On Tue, 26 Mar 2024 14:46:10 +0000 > > Mark Rutland <mark.rutl...@arm.com> wrote: > > > > > Hi Masami, > > > > > > On Mon, Mar 25, 2024 at 11:56:32AM +0900, Masami Hiramatsu wrote: > > > > Hi Jarkko, > > > > > > > > On Sun, 24 Mar 2024 01:29:08 +0200 > > > > Jarkko Sakkinen <jar...@kernel.org> wrote: > > > > > > > > > Tracing with kprobes while running a monolithic kernel is currently > > > > > impossible due the kernel module allocator dependency. > > > > > > > > > > Address the issue by allowing architectures to implement > > > > > module_alloc() > > > > > and module_memfree() independent of the module subsystem. An arch tree > > > > > can signal this by setting HAVE_KPROBES_ALLOC in its Kconfig file. > > > > > > > > > > Realize the feature on RISC-V by separating allocator to > > > > > module_alloc.c > > > > > and implementing module_memfree(). > > > > > > > > Even though, this involves changes in arch-independent part. So it > > > > should > > > > be solved by generic way. Did you checked Calvin's thread? > > > > > > > > https://lore.kernel.org/all/cover.1709676663.git.jcalvinow...@gmail.com/ > > > > > > > > I think, we'd better to introduce `alloc_execmem()`, > > > > CONFIG_HAVE_ALLOC_EXECMEM and CONFIG_ALLOC_EXECMEM at first > > > > > > > > config HAVE_ALLOC_EXECMEM > > > > bool > > > > > > > > config ALLOC_EXECMEM > > > > bool "Executable trampline memory allocation" > > > > depends on MODULES || HAVE_ALLOC_EXECMEM > > > > > > > > And define fallback macro to module_alloc() like this. > > > > > > > > #ifndef CONFIG_HAVE_ALLOC_EXECMEM > > > > #define alloc_execmem(size, gfp) module_alloc(size) > > > > #endif > > > > > > Please can we *not* do this? I think this is abstracting at the wrong > > > level (as > > > I mentioned on the prior execmem proposals). > > > > > > Different exectuable allocations can have different requirements. For > > > example, > > > on arm64 modules need to be within 2G of the kernel image, but the > > > kprobes XOL > > > areas can be anywhere in the kernel VA space. > > > > > > Forcing those behind the same interface makes things *harder* for > > > architectures > > > and/or makes the common code more complicated (if that ends up having to > > > track > > > all those different requirements). From my PoV it'd be much better to have > > > separate kprobes_alloc_*() functions for kprobes which an architecture > > > can then > > > choose to implement using a common library if it wants to. > > > > > > I took a look at doing that using the core ifdeffery fixups from Jarkko's > > > v6, > > > and it looks pretty clean to me (and works in testing on arm64): > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=kprobes/without-modules > > > > > > Could we please start with that approach, with kprobe-specific alloc/free > > > code > > > provided by the architecture? > > Heh, I also noticed that dead !RWX branch in arm64 patch_map(), I was > about to send a patch to remove it. > > > OK, as far as I can read the code, this method also works and neat! > > (and minimum intrusion). I actually found that exposing CONFIG_ALLOC_EXECMEM > > to user does not help, it should be an internal change. So hiding this > > change > > from user is better choice. Then there is no reason to introduce the new > > alloc_execmem, but just expand kprobe_alloc_insn_page() is reasonable. > > I'm happy with this, it solves the first half of my problem. But I want > eBPF to work in the !MODULES case too. > > I think Mark's approach can work for bpf as well, without needing to > touch module_alloc() at all? So I might be able to drop that first patch > entirely.
Yeah, I think we're aligned. Later on, if/when you send the bpf series please also cc me and I might possibly test those patches too. BR, Jarkko
