On Sun, Jul 26, 2020 at 11:14:08AM +0300, Mike Rapoport wrote: > On Sat, Jul 25, 2020 at 06:16:48AM +0300, Jarkko Sakkinen wrote: > > > I've read the observations in the other threads, but this #ifdef > > > jungle is silly, it's a de-facto open coded text_alloc() with a > > > module_alloc() fallback... > > > > In the previous version I had: > > > > https://lore.kernel.org/lkml/20200717030422.679972-4-jarkko.sakkinen@xxxxxxxxxxxxxxx/ > > > > and I had just calls to text_alloc() and text_free() in corresponding > > snippet to the above. > > > > I got this feedback from Mike: > > > > https://lore.kernel.org/lkml/20200718162359.GA2919062@xxxxxxxxxx/ > > > > I'm not still sure that I fully understand this feedback as I don't see > > any inherent and obvious difference to the v4. In that version fallbacks > > are to module_alloc() and module_memfree() and text_alloc() and > > text_memfree() can be overridden by arch. > > Let me try to elaborate. > > There are several subsystems that need to allocate memory for executable > text. As it happens, they use module_alloc() with some abilities for > architectures to override this behaviour. > > For many architectures, it would be enough to rename modules_alloc() to > text_alloc(), make it built-in and this way allow removing dependency on > MODULES. > > Yet, some architectures have different restrictions for code allocation > for different subsystems so it would make sense to have more than one > variant of text_alloc() and a single config option ARCH_HAS_TEXT_ALLOC > won't be sufficient. > > I liked Mark's suggestion to have text_alloc_<something>() and proposed > a way to introduce text_alloc_kprobes() along with > HAVE_KPROBES_TEXT_ALLOC to enable arch overrides of this function. > > The major difference between your v4 and my suggestion is that I'm not > trying to impose a single ARCH_HAS_TEXT_ALLOC as an alternative to > MODULES but rather to use per subsystem config option, e.g. > HAVE_KPROBES_TEXT_ALLOC. > > Another thing, which might be worth doing regardless of the outcome of > this discussion is to rename alloc_insn_pages() to text_alloc_kprobes() > because the former is way too generic and does not emphasize that the > instruction page is actually used by kprobes only. What if we in kernel/kprobes.c just: #ifndef CONFIG_ARCH_HAS_TEXT_ALLOC void __weak *alloc_insn_page(void) { return module_alloc(PAGE_SIZE); } void __weak free_insn_page(void *page) { module_memfree(page); } #endif In Kconfig (as in v5): config KPROBES bool "Kprobes" depends on MODULES || ARCH_HAS_TEXT_ALLOC I checked architectures that override alloc_insn_page(). With the exception of x86, they do not call module_alloc(). If no rename was done, then with this approach a more consistent. config flag name would be CONFIG_ARCH_HAS_ALLOC_INSN_PAGE. I'd call the function just as kprobes_alloc_page(). Then the config flag would become CONFIG_HAS_KPROBES_ALLOC_PAGE. > -- > Sincerely yours, > Mike. Thanks for the feedback! /Jarkko
