From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 62BA642A15F; Fri, 17 Jul 2026 14:20:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784298048; cv=none; b=ug9h/hvscuT3lI9SzB0pQiheKMWVHw0YbeMLgXrzDkXV7fYvVZb9uGS4xhRHkH7iYl+YCmuUHYiDizMesOjfiZtDjMIhk0QJWhV5Aj2pTMOmlHTFlrBznEXJo337a1sEfpv6Wd8tK7pmw1o2JRWwdWlHwDONTecGzZwscQzNICE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784298048; c=relaxed/simple; bh=/T5lEK8DJeQPkBZw1CJanRPUc6l9C5N4tGXaiQE6buc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Pq+/RHPNioaCMV7fTkTS7RhqvHlKvAUrypyYjZwSyxoIZEzoXAr9Fd7b8bj71np25kud5Q1eaJ9x8gNYyOBS/kpi9ayB52uSYOfnLYvuG3xvYZJ8Ghp4/Hpkg5Kdk70ldtPlIAcqOHYzIKb+Jg4g8wyTNMWtsuzYSnWroJBbfOM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WN4XQA21; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WN4XQA21" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4050C1F000E9; Fri, 17 Jul 2026 14:20:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784298047; bh=rk2umw+DZv1nSqIyLtphMjlVQouL5ewpaGHrx+pr8O4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WN4XQA21Xc+dwUSbx7L/9wvHiSlSrZJ1R6gmeC7IWtxGskFqF9zMCExDQmJpWDWHb y6w8JksGXdYv1lIiWv0iYvTAX6GTRrwpXoxd7qxzXa+EruaSzHy5acjMU5wDSFI84H oQHNU1ACtUPkoY2GetnNIqooh0XqUZaag8Clll+LM4An555VL0w1NPVJEM8I05AmOF Aw5Sv9ToYMKsRzErtMxdEuWoesdN5DCh6y+Mj50lYPBci3tCrKbjCR+I+8cqMDNAnJ X6nZ5LV9kcvbDjmaBbqNpMQkqGjK0TSf3kVe8GiCCGEUPlhtdznXFXyHfYw+aRCXhw 5YqsN0P7ZdFUw== From: "Masami Hiramatsu (Google)" To: Steven Rostedt , Peter Zijlstra , Ingo Molnar , x86@kernel.org Cc: Jinchao Wang , Mathieu Desnoyers , Masami Hiramatsu , 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: [PATCH v9 06/10] x86/hw_breakpoint: Add arch_reinstall_hw_breakpoint Date: Fri, 17 Jul 2026 23:20:41 +0900 Message-ID: <178429804092.157981.15678603723493216503.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178429796992.157981.3393977217853767915.stgit@devnote2> References: <178429796992.157981.3393977217853767915.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Jinchao Wang The new arch_reinstall_hw_breakpoint() function can be used in an atomic context, unlike the more expensive free and re-allocation path. This allows callers to efficiently re-establish an existing breakpoint. Signed-off-by: Jinchao Wang Reviewed-by: Masami Hiramatsu (Google) --- Changes in v9: - Update commit message. - Temporarily disable the active slot in setup_hwbp() before updating the address register to avoid spurious debug exceptions. --- arch/x86/include/asm/hw_breakpoint.h | 2 ++ arch/x86/kernel/hw_breakpoint.c | 34 ++++++++++++++++++++++++++++------ 2 files changed, 30 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h index aa6adac6c3a2..c22cc4e87fc5 100644 --- a/arch/x86/include/asm/hw_breakpoint.h +++ b/arch/x86/include/asm/hw_breakpoint.h @@ -21,6 +21,7 @@ struct arch_hw_breakpoint { enum bp_slot_action { BP_SLOT_ACTION_INSTALL, + BP_SLOT_ACTION_REINSTALL, BP_SLOT_ACTION_UNINSTALL, }; @@ -65,6 +66,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused, int arch_install_hw_breakpoint(struct perf_event *bp); +int arch_reinstall_hw_breakpoint(struct perf_event *bp); void arch_uninstall_hw_breakpoint(struct perf_event *bp); void hw_breakpoint_pmu_read(struct perf_event *bp); void hw_breakpoint_pmu_unthrottle(struct perf_event *bp); diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index c323c2aab2af..0df3ff556f47 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -100,6 +100,10 @@ static int manage_bp_slot(struct perf_event *bp, enum bp_slot_action action) old_bp = NULL; new_bp = bp; break; + case BP_SLOT_ACTION_REINSTALL: + old_bp = bp; + new_bp = bp; + break; case BP_SLOT_ACTION_UNINSTALL: old_bp = bp; new_bp = NULL; @@ -129,23 +133,36 @@ static int manage_bp_slot(struct perf_event *bp, enum bp_slot_action action) static void setup_hwbp(struct arch_hw_breakpoint *info, int slot, bool enable) { unsigned long dr7; - - set_debugreg(info->address, slot); - __this_cpu_write(cpu_debugreg[slot], info->address); + bool enabled; dr7 = this_cpu_read(cpu_dr7); + enabled = dr7 & ((DR_LOCAL_ENABLE | DR_GLOBAL_ENABLE) << (slot * DR_ENABLE_SIZE)); dr7 &= ~(__encode_dr7(slot, 0xc, 0x3) | (DR_LOCAL_ENABLE << (slot * DR_ENABLE_SIZE))); - if (enable) - dr7 |= encode_dr7(slot, info->len, info->type); + + /* + * If the slot is currently enabled, disable it first before updating + * the address register to prevent spurious debug exceptions. + */ + if (enable && enabled) { + barrier(); + set_debugreg(dr7, 7); + barrier(); + this_cpu_write(cpu_dr7, dr7); + } + + set_debugreg(info->address, slot); + __this_cpu_write(cpu_debugreg[slot], info->address); /* * Enabling: * Ensure we first write cpu_dr7 before we set the DR7 register. * This ensures an NMI never see cpu_dr7 0 when DR7 is not. */ - if (enable) + if (enable) { + dr7 |= encode_dr7(slot, info->len, info->type); this_cpu_write(cpu_dr7, dr7); + } barrier(); @@ -189,6 +206,11 @@ int arch_install_hw_breakpoint(struct perf_event *bp) return arch_manage_bp(bp, BP_SLOT_ACTION_INSTALL); } +int arch_reinstall_hw_breakpoint(struct perf_event *bp) +{ + return arch_manage_bp(bp, BP_SLOT_ACTION_REINSTALL); +} + void arch_uninstall_hw_breakpoint(struct perf_event *bp) { arch_manage_bp(bp, BP_SLOT_ACTION_UNINSTALL);