From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D9336EB75; Tue, 16 Apr 2024 07:23:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713252206; cv=none; b=VHkeyzIbKbKGyGXLYc8WCAkzSIf45pmkXFPO39XulTqCp8JJt/VEmI/5zqg1Jqo6Wmy/ZVyh5thfkGWRbDRnp74yq47yDxrd7F053nt8oEP+d4VPJgUEmNNM5xh9f+yPPiB28qE+352P3m7l/fO/+G+uFsyTPbXrNkjMhaV64ZI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713252206; c=relaxed/simple; bh=ULqJjlTCraVJ0ruf913jYz2dlG1gS6UCOgmOiRdXRlo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UjCvUPLzf0P3JLPBqJW2/Sn+xfkNer8nzPpJ1PQZr0VieC5pN2cPRDtF86WlRWoIMN163+SoQ1iEKRXtCwXwxWKOfl+DcQCsuFTcPeEUDF3NH+HFL84kVCy3ArKqnHlZf/m0tWDuZLJTDnBDJy2NWegGodnzs2laWUFeMHkhecM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ekk8HCBF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ekk8HCBF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2BBECC113CE; Tue, 16 Apr 2024 07:23:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713252205; bh=ULqJjlTCraVJ0ruf913jYz2dlG1gS6UCOgmOiRdXRlo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ekk8HCBFjthC7O7PxrFN7j/GM7z/nWOuO8k9QOUSLiGyz09GAO2cg64dmGZlUlds7 00Ewxyx3C6wcPZBoIkKGD6lbL3qbO2ksVpnRUlonLdQr9BhpV1yf7+bx9loZNn41At rywVk+bWOXuipnXUZImOPnzXQlyIpQamAXCi97V5XEUtgpABiSiT97flmkQAEFDr7A YcuRY0rwjZPTJIRXEph9PF+jUZc4mOVTGomsCx8EugJ6WC8EEbdEckfhASAJlczMAM pEgjXqHCw7T7cVdoBUzlejwen9ZBJYRh+vjYrzCI4CZ6xsCi82SwkYS2yHPnvfOsma Wo31Nl9r7Gz/Q== Date: Tue, 16 Apr 2024 10:22:14 +0300 From: Mike Rapoport To: Mark Rutland Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Alexandre Ghiti , Andrew Morton , "Bj\"orn T\"opel" , Catalin Marinas , Christophe Leroy , "David S. Miller" , Dinh Nguyen , Donald Dutile , Eric Chanudet , Heiko Carstens , Helge Deller , Huacai Chen , Kent Overstreet , Luis Chamberlain , Michael Ellerman , Nadav Amit , Palmer Dabbelt , Puranjay Mohan , Rick Edgecombe , Russell King , Song Liu , Steven Rostedt , Thomas Bogendoerfer , Thomas Gleixner , Will Deacon , bpf@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev, netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free() Message-ID: References: <20240411160051.2093261-1-rppt@kernel.org> <20240411160051.2093261-6-rppt@kernel.org> <20240415075241.GF40213@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-mips@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Apr 15, 2024 at 06:36:39PM +0100, Mark Rutland wrote: > On Mon, Apr 15, 2024 at 09:52:41AM +0200, Peter Zijlstra wrote: > > On Thu, Apr 11, 2024 at 07:00:41PM +0300, Mike Rapoport wrote: > > > +/** > > > + * enum execmem_type - types of executable memory ranges > > > + * > > > + * There are several subsystems that allocate executable memory. > > > + * Architectures define different restrictions on placement, > > > + * permissions, alignment and other parameters for memory that can be used > > > + * by these subsystems. > > > + * Types in this enum identify subsystems that allocate executable memory > > > + * and let architectures define parameters for ranges suitable for > > > + * allocations by each subsystem. > > > + * > > > + * @EXECMEM_DEFAULT: default parameters that would be used for types that > > > + * are not explcitly defined. > > > + * @EXECMEM_MODULE_TEXT: parameters for module text sections > > > + * @EXECMEM_KPROBES: parameters for kprobes > > > + * @EXECMEM_FTRACE: parameters for ftrace > > > + * @EXECMEM_BPF: parameters for BPF > > > + * @EXECMEM_TYPE_MAX: > > > + */ > > > +enum execmem_type { > > > + EXECMEM_DEFAULT, > > > + EXECMEM_MODULE_TEXT = EXECMEM_DEFAULT, > > > + EXECMEM_KPROBES, > > > + EXECMEM_FTRACE, > > > + EXECMEM_BPF, > > > + EXECMEM_TYPE_MAX, > > > +}; > > > > Can we please get a break-down of how all these types are actually > > different from one another? > > > > I'm thinking some platforms have a tiny immediate space (arm64 comes to > > mind) and has less strict placement constraints for some of them? > > Yeah, and really I'd *much* rather deal with that in arch code, as I have said > several times. > > For arm64 we have two bsaic restrictions: > > 1) Direct branches can go +/-128M > We can expand this range by having direct branches go to PLTs, at a > performance cost. > > 2) PREL32 relocations can go +/-2G > We cannot expand this further. > > * We don't need to allocate memory for ftrace. We do not use trampolines. > > * Kprobes XOL areas don't care about either of those; we don't place any > PC-relative instructions in those. Maybe we want to in future. > > * Modules care about both; we'd *prefer* to place them within +/-128M of all > other kernel/module code, but if there's no space we can use PLTs and expand > that to +/-2G. Since modules can refreence other modules, that ends up > actually being halved, and modules have to fit within some 2G window that > also covers the kernel. > > * I'm not sure about BPF's requirements; it seems happy doing the same as > modules. BPF are happy with vmalloc(). > So if we *must* use a common execmem allocator, what we'd reall want is our own > types, e.g. > > EXECMEM_ANYWHERE > EXECMEM_NOPLT > EXECMEM_PREL32 > > ... and then we use those in arch code to implement module_alloc() and friends. I'm looking at execmem_types more as definition of the consumers, maybe I should have named the enum execmem_consumer at the first place. And the arch constrains defined in struct execmem_range describe how memory should be allocated for each consumer. These constraints are defined early at boot and remain static, so initializing them once and letting a common allocator use them makes perfect sense to me. I agree that fallback_{start,end} are not ideal, but we have 3 architectures that have preferred and secondary range for modules. And arm and powerpc use the same logic for kprobes as well, and I don't see why this code should be duplicated. And, for instance, if you decide to place PC-relative instructions if kprobes XOL areas, you'd only need to update execmem_range for kprobes to be more like the range for modules. With central allocator it's easier to deal with the things like VM_FLUSH_RESET_PERMS and caching of ROX memory and I think it will be more maintainable that module_alloc(), alloc_insn_page() and bpf_jit_alloc_exec() spread all over the place. > Mark. -- Sincerely yours, Mike.