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[85.193.35.130]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5d652ab50desm252025a12.3.2024.12.13.13.52.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Dec 2024 13:52:25 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 13 Dec 2024 22:52:23 +0100 To: Peter Zijlstra Cc: Jiri Olsa , Oleg Nesterov , Andrii Nakryiko , bpf@vger.kernel.org, Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next 00/13] uprobes: Add support to optimize usdt probes on x86_64 Message-ID: References: <20241211133403.208920-1-jolsa@kernel.org> <20241213105105.GB35539@noisy.programming.kicks-ass.net> <20241213135433.GD35539@noisy.programming.kicks-ass.net> <20241213183954.GC12338@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-trace-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: <20241213183954.GC12338@noisy.programming.kicks-ass.net> On Fri, Dec 13, 2024 at 07:39:54PM +0100, Peter Zijlstra wrote: > On Fri, Dec 13, 2024 at 03:05:54PM +0100, Jiri Olsa wrote: > > On Fri, Dec 13, 2024 at 02:54:33PM +0100, Peter Zijlstra wrote: > > > On Fri, Dec 13, 2024 at 02:07:54PM +0100, Jiri Olsa wrote: > > > > On Fri, Dec 13, 2024 at 11:51:05AM +0100, Peter Zijlstra wrote: > > > > > On Wed, Dec 11, 2024 at 02:33:49PM +0100, Jiri Olsa wrote: > > > > > > hi, > > > > > > this patchset adds support to optimize usdt probes on top of 5-byte > > > > > > nop instruction. > > > > > > > > > > > > The generic approach (optimize all uprobes) is hard due to emulating > > > > > > possible multiple original instructions and its related issues. The > > > > > > usdt case, which stores 5-byte nop seems much easier, so starting > > > > > > with that. > > > > > > > > > > > > The basic idea is to replace breakpoint exception with syscall which > > > > > > is faster on x86_64. For more details please see changelog of patch 8. > > > > > > > > > > So ideally we'd put a check in the syscall, which verifies it comes from > > > > > one of our trampolines and reject any and all other usage. > > > > > > > > > > The reason to do this is that we can then delete all this code the > > > > > moment it becomes irrelevant without having to worry userspace might be > > > > > 'creative' somewhere. > > > > > > > > yes, we do that already in SYSCALL_DEFINE0(uprobe): > > > > > > > > /* Allow execution only from uprobe trampolines. */ > > > > vma = vma_lookup(current->mm, regs->ip); > > > > if (!vma || vma->vm_private_data != (void *) &tramp_mapping) { > > > > force_sig(SIGILL); > > > > return -1; > > > > } > > > > > > Ah, right I missed that. Doesn't that need more locking through? The > > > moment vma_lookup() returns that vma can go bad. > > > > ugh yes.. I guess mmap_read_lock(current->mm) should do, will check > > If you check > tip/perf/core:kernel/events/uprobe.c:find_active_uprobe_speculative() > you'll find means of doing it locklessly using RCU. right, will use that thanks, jirka