From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oo1-f52.google.com (mail-oo1-f52.google.com [209.85.161.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EDB233242DF for ; Thu, 6 Aug 2026 02:58:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785985126; cv=none; b=A3nPj0QQ9MgFJ5i30HkbyshtkQ+cJ8DWASjuHJKmwu1bUdxHmy7d19sLGG/5BUU7cqsuC3GeD375zsl0Ibe3ZZT3CqtXxqNQ3chDF2Qj17dGaswFO7iZ1rvGXsr7s2Rul3+nOYqiHJjWXVg03S7BX/3pcAcg5povNe3qQa7TSrw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785985126; c=relaxed/simple; bh=fsWRZDHmdhpEVey7PNeiNthgILPDQgnkk9V8OIsmTHY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Lh7APtwhUtQ11jbkmZbknyeo38IfwVk39JTGyI837wAPkoSvsdd9ihHfLkKdz9tK6ooweyUU5oBGit8lXdwWeADI8Qa/BWxg22LEZ3RUadrgs7hUMKt5FS6wIBDk/pXIwME+uYfz63ryocZyJmTNr+BX8/39bkLYuCi8nbIC/5E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=LKDW0I+T; arc=none smtp.client-ip=209.85.161.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="LKDW0I+T" Received: by mail-oo1-f52.google.com with SMTP id 006d021491bc7-6b01abe5cdbso1286eaf.3 for ; Wed, 05 Aug 2026 19:58:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1785985122; x=1786589922; darn=vger.kernel.org; h=content-transfer-encoding:content-type:in-reply-to:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:from:to:cc:subject:date:message-id:reply-to:content-type; bh=Cb3qpMNSQjkPFBRsgWqX2QuJCQXNljC6fDwPCJ7VZBs=; b=LKDW0I+TS5kgEgK5PhYaJHnShgS6TQ69xoyA9jq00AsOqWA6ZXC3bpIWJOSNjOrZ+V +0B8gISScl19XWere4KZOr7GItxoxVqmVmavHTTLlTe94vnSDzwPjgksiCBoF55PwB8A BuQHRWSSNs3YUtGX66F2aB+oMd0X72WsxxAXZiIu8LycsUSB4hfc4SdzintLZLntxaQu lxk3tB3f6lx5rheFOkVkMu8WPFu7lftePgBPpHuDm+oSKSPj8x347aGDNrlUGOXtqHZ1 Bqe4TwzupE98ZPkyZVC6ZB/xLU69VGZc/4XSdBmwlYOuMmhpHy1Q/td9cjKgX5k4jw4Y lfaQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785985122; x=1786589922; h=content-transfer-encoding:content-type:in-reply-to:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=Cb3qpMNSQjkPFBRsgWqX2QuJCQXNljC6fDwPCJ7VZBs=; b=VbjK3VgzpjznufMEl3yw0Xo5jVgpHPB66o5Ezy2cCUajPooJ+tuTG68iTNvzhPZv0R 0yPeqvzIEyrlOQzUxnqr26JxU+LtFNwOpiaxkRPeMXc7XulvpBVIYEFPJ5n7bo7seZmO cS4abjh+q0Zx1jDeXr3tifnEO7k3DR12RqpdofTQRI3aoG3HwRJkBqQ9Ekain/wdGXK5 L322sUsG5XigIgAtwo7gtuQBKd35r6P2RYE89H2imDtwDTzWHt+NC1m23DLE0l6Pkm2u 1XSAmwwPWwmjZySK2GPOwKjeTZIRQSvoRCNLC+uo1ispSMHYoSgyk37fVPvvmf0bmBK6 kAGA== X-Forwarded-Encrypted: i=1; AHgh+RoXz0BfkFIFosU/jGz+g1LewuZGK5i2voPvIz8LudBgakgxr8A67QkCJ7JObQKARcsm7CJWLwE5P4V1Evr1TV2rPlM=@vger.kernel.org X-Gm-Message-State: AOJu0YwAytO5GNgc54L0CEukZatY68RHfUT9EbjWfnb+hO0316pk5SwZ gZcJkUUmOeq8ZCVa8/DBPnOlgFOsKYJ1SaA2Qrw3HSreO0LZ0PPmy5Br X-Gm-Gg: AR+sD12dTvLmh5lFLAechaAv0/+HH1xT46D5iDULoK3eTaCJxrHlZEg9vCP9VpOjZiX agXRW2jo+U2KTKo+PSRz4CkPVvd73Yf+CIgqC6gHKA7FlacNC0/tZuaBFPair07hYIPUwxS+bFJ vCxKVdCI3gNiGp82Tsfi551vyrbNdBLthIL4+ItKImgqlA33SzDWjX8bqiV1NoBtw3Y24xA0dcn LazYsMX35SIBPGeKrO3Y/fieEb+IZyzF6s+2Nuw3HVAgQJw/oD5yOqgQqxDlDIbMdx0Z0Ik5tsD VCd+V/W4YE9qgPMvUZ2NISyGT5ueMLjq/CokaQHlFu8RL20HrHDzDG2Pz3JzOeacw1IiKtHVwDv QmfLk4Exm/4/GXGdLBXTbQG6E/dH1eCeydINnvOY+LJi290FTOS/xTobYOWArnYH/bLG7She+py PR2wpGlLDWJJ/P2iBlQaVuNEVhb6dCwpnImtnBTQ2f9XQEE9bjbbMQS+brzbunu9o= X-Received: by 2002:a05:6820:4dcd:b0:6a1:363d:bc42 with SMTP id 006d021491bc7-6ae96c55f8fmr6311046eaf.15.1785985121804; Wed, 05 Aug 2026 19:58:41 -0700 (PDT) Received: from [127.0.0.1] ([144.24.58.22]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-6ae93cbf7a9sm4532734eaf.2.2026.08.05.19.58.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Aug 2026 19:58:41 -0700 (PDT) Message-ID: Date: Thu, 6 Aug 2026 10:58:27 +0800 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 04/11] tracing: wprobe: Add watchpoint probe event based on hardware breakpoint Content-Language: en-US To: "Masami Hiramatsu (Google)" , Peter Zijlstra Cc: Steven Rostedt , Ingo Molnar , x86@kernel.org, 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 References: <178565870538.714490.11309825813968306287.stgit@devnote2> <178565875046.714490.17724442147958346980.stgit@devnote2> <20260803070356.GV49951@noisy.programming.kicks-ass.net> <20260804080035.6b719368c9328bbdd8219867@kernel.org> <20260803230840.GJ687043@noisy.programming.kicks-ass.net> <20260806090641.e59484ac570b0f842bc930bc@kernel.org> From: Jinchao Wang In-Reply-To: <20260806090641.e59484ac570b0f842bc930bc@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/6/2026 8:06 AM, Masami Hiramatsu (Google) wrote: > On Tue, 4 Aug 2026 01:08:40 +0200 > Peter Zijlstra wrote: > >> 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? > > Ahh, sorry. It was misreading, I mean it should be only for the kernel address, > not for user space. So I don't want to add userspace. (I answered the first one) > > Thank you, > Keeping wprobe limited to kernel addresses makes sense to me. Userspace watchpoints are already supported by the perf hardware-breakpoint API, and supporting them in wprobe would add unnecessary complexity. An explicit address check could also make this boundary clear. >> >> That is, don't paint yourself in a corner etc. > >