From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 2E1A03446C3; Mon, 3 Aug 2026 23:08:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785798529; cv=none; b=ksmrT82aO/WCfvjXvHk0c7ZQorq0rHX9XS9TyuLWWmZuiWQHRJzFtUPFmdzflF8dwUiXlBJHyTCOro/6ibJLSCnZilUFEenEG+CpN2G6HH2WwncGASppqzV8N9ZKP88vrElxtj3mFDvE+gcuJ3wTHXfBasHG3NXD8nsv7vACKjc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785798529; c=relaxed/simple; bh=HoglUgCFZoEowKApPKS9MhwYlbuRhQEtX7E3nLI4538=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=i5dlAPWvgDk6rcHNvZkAJT5jwUPm+mUQ4So48gHNIoXFL77j8OS37f1hz8YARRyjGwLKM2QgOlCrdIRxPY43XkDB0KmteKk3opkms71nVGnfKiOIvdjvHxoU1U9E0Eftus954yw4oAjjZ63WtsHgZcRlDpqoF8AWodYDRChJsIE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=r9XjxFXa; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="r9XjxFXa" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=SA2dlnI/MmT0FWL+U+ME23/wbCe0VZl/s+QIV1MkBtw=; b=r9XjxFXaz1up9cUV50ogjUWrgP Z260+h9zsDsYaWRu4v6IDKcju+bfpqvIovDkVaSoyhay+iHjpjJEL/f322FSLPRqGWrP/QbtwWyuM G+wOiW61XX4HeLl2uMM36AhrrC3jA3mlV1rqvIg4pkQlpH7zP/fGBQn00kZNLQgS5eG3lCFaRlMW+ 9ixao8CbFZGtfXQow4bYrAseHGFIdvhaKBj4QL8kmUUa2fIEEJACgSjWdvWm59o31jE6mx9rlYo9J VzWdS8KQ525mUZ9ozQWg+qTjD871iKgFKb0FObM3KVIK2/alBuoYyEuUC8QSPEFY6beOUEmb/py40 hRXIjqZg==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wr1lw-0000000Ewpj-2aXh; Mon, 03 Aug 2026 23:08:40 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 427B030063F; Tue, 04 Aug 2026 01:08:40 +0200 (CEST) Date: Tue, 4 Aug 2026 01:08:40 +0200 From: Peter Zijlstra To: Masami Hiramatsu Cc: Steven Rostedt , Ingo Molnar , x86@kernel.org, Jinchao Wang , Mathieu Desnoyers , Thomas Gleixner , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Alexander Shishkin , Ian Rogers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH v11 04/11] tracing: wprobe: Add watchpoint probe event based on hardware breakpoint Message-ID: <20260803230840.GJ687043@noisy.programming.kicks-ass.net> References: <178565870538.714490.11309825813968306287.stgit@devnote2> <178565875046.714490.17724442147958346980.stgit@devnote2> <20260803070356.GV49951@noisy.programming.kicks-ass.net> <20260804080035.6b719368c9328bbdd8219867@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@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: <20260804080035.6b719368c9328bbdd8219867@kernel.org> On Tue, Aug 04, 2026 at 08:00:35AM +0900, Masami Hiramatsu wrote: > On Mon, 3 Aug 2026 09:03:56 +0200 > Peter Zijlstra wrote: > > > On Sun, Aug 02, 2026 at 05:19:10PM +0900, Masami Hiramatsu (Google) wrote: > > > From: Masami Hiramatsu (Google) > > > > > > Add a new probe event for the hardware breakpoint called wprobe-event. > > > This wprobe allows user to trace (watch) the memory access at the > > > specified memory address. > > > > s/the memory/the kernel memory/ > > Indeed. > > > > > > The new syntax is; > > > > > > w[:[GROUP/]EVENT] [r|w|rw]@[ADDR|SYM][:SIZE] [FETCH_ARGs] > > > > > > User also can use $addr to fetch the accessed address and $value to fetch > > > the accessed memory value (shorthand for '+0($addr)'). No other variables > > > are supported. > > > > This seems limited to kernel addresses only? Should not also userspace > > addresses be supported? > > Hmm, for x86, yes, since it causes a trap after executing (all page fault > are handled). But other architecture like arm64 may not be able to support > it because it needs to enable watchpoint after major page fault. > At this step, I would like to limit it just for kernel memory. Sure, but suppose you were to add userspace, what would the ABI be? That is, don't paint yourself in a corner etc.