From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CE30D4A0A; Tue, 26 Mar 2024 16:45:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711471527; cv=none; b=E1zO2qCVZ5Ma7JnpmtadBhuW0Xb9e5qDpWOECITCGD9Eu6RHaXEhSDnnZEXYv07OqbqYr9HqlbZt1KaUJwjZOtOcsloB6BPFmENpZLoGH7eaPpJaW4Lvxev65GakBSPEv1V40SMGVkoUBdCptXWK1wgImGJDerJmr6lL5jfJjKg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711471527; c=relaxed/simple; bh=e95uhVBTfAzZnFOKr0O1j5p3MLRuxzZEWptMHK7NSpA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H7WfTXi0r/0u6fRQxwC+iyRYBOlvhfytFHiJK69sRd9+W6khzEK7dhB+bLyliRagaAGzOdOEi6sRWBcpsaqLAqhZ6N7KgxJ5afTjMiq4yegHH097pOZNTwVx2gV5ub92nbYEfUxrk+k0A+JApuMRRYdRGQJOyKRBvDOY34Vv7q4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A8D5F2F4; Tue, 26 Mar 2024 09:45:58 -0700 (PDT) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.35.184]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5B7D93F694; Tue, 26 Mar 2024 09:45:23 -0700 (PDT) Date: Tue, 26 Mar 2024 16:45:20 +0000 From: Mark Rutland To: Calvin Owens Cc: Masami Hiramatsu , Jarkko Sakkinen , linux-riscv@lists.infradead.org, Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-kernel@vger.kernel.org, "Naveen N . Rao" , Anil S Keshavamurthy , "David S . Miller" , linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v2] arch/riscv: Enable kprobes when CONFIG_MODULES=n Message-ID: References: <20240323232908.13261-1-jarkko@kernel.org> <20240325115632.04e37297491cadfbbf382767@kernel.org> <20240327002403.62649aee45508b7a16caedba@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@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 Tue, Mar 26, 2024 at 09:15:14AM -0700, 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 wrote: > > > 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. I'd be very happy with eBPF following the same approach, with BPF-specific alloc/free functions that we can implement in arch code. IIUC eBPF code *does* want to be within range of the core kernel image, so for arm64 we'd want to factor some common logic out of module_alloc() and into something that module_alloc() and "bpf_alloc()" (or whatever it would be called) could use. So I don't think we'd necessarily save on touching module_alloc(), but I think the resulting split would be better. Thanks, Mark.