From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 1E7672F530A; Tue, 17 Jun 2025 22:49:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750200582; cv=none; b=mANhAP/0tDo4dS7xymquDBm+ZtBys4rERltX/UPqrIjQIzgBiAuRpp0aybnMHfaesSGZrlEP2dQwZzdmYEjWG82Di2QdYdQkWQVEn1KbO6MG6dEZ/H5VFV1kA7Pick7XHvLpcm4SIxhe4hW9kEH/BATccHqSnAzds4zhif1CtAU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750200582; c=relaxed/simple; bh=+418RPPEpMl6R1nIeDIqqt6kT5AmLgaQLrpG11zA7DQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=aa9X4jPssHq10m6CQq/kKsRftopf5f9wFDeu9KMQfXfKD4csR55yXbQVAzCetQB2pn7XgUeH/mXAp60n5HH04i6/yeB0q43ASNPH50CLFPlXnTOiMyM8i1SxOyCEH+LRMxQ2/pJ2ri2MreNtU+trs2HIO29k4YUUpWcET6ty5n4= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=oxD2FvHdmWeI5aPqZ8d2wwrKnhwJdagX4vCZgrdG/Giwz/VgCfSBibb/AJr0DlsGQ aDG0B9mprdY6fzoqiprxpq5QF/Ks/lu4koyKaQgEU4aaI6zQMAPZbQE3tSjuv/ie/o rnLmVet5SCNbrxaynepHxZofaaH8YKfTYhCJah4w+pWcJybNbRWw9WnEOeOIJWV4Ye qImy8PFoYDwKK8cllAiWriybeLU/V5WaZJWrE4RAdYmea4uV8hiwcC5+X/rwfgqu7E 91+Jgb0lDEHmMqHyfPXe2Mrqt5JJdN/CmN2aC0OMk4n6mnFvG2KIb1BJSA+hCSWoDr XpMppk6nMekQw== Message-ID: <3e4c2e32-3c12-47a6-bf84-79690f78e1bf@zytor.com> Date: Tue, 17 Jun 2025 15:49:00 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] x86/traps: Initialize DR6 by writing its architectural reset value To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, seanjc@google.com, pbonzini@redhat.com, sohil.mehta@intel.com, brgerst@gmail.com, tony.luck@intel.com, fenghuay@nvidia.com References: <20250617073234.1020644-1-xin@zytor.com> <20250617073234.1020644-2-xin@zytor.com> <20250617090329.GO1613376@noisy.programming.kicks-ass.net> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/17/2025 2:03 AM, Peter Zijlstra wrote: > On Tue, Jun 17, 2025 at 12:32:33AM -0700, Xin Li (Intel) wrote: >> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c >> index 8feb8fd2957a..3bd7c9ac7576 100644 >> --- a/arch/x86/kernel/cpu/common.c >> +++ b/arch/x86/kernel/cpu/common.c >> @@ -2243,20 +2243,17 @@ EXPORT_PER_CPU_SYMBOL(__stack_chk_guard); >> #endif >> #endif >> >> -/* >> - * Clear all 6 debug registers: >> - */ >> -static void clear_all_debug_regs(void) >> +static void initialize_debug_regs(void) >> { >> int i; >> >> - for (i = 0; i < 8; i++) { >> - /* Ignore db4, db5 */ >> - if ((i == 4) || (i == 5)) >> - continue; >> + /* Control register first */ >> + set_debugreg(0, 7); >> + set_debugreg(DR6_RESERVED, 6); >> >> + /* Ignore db4, db5 */ >> + for (i = 0; i < 4; i++) >> set_debugreg(0, i); >> - } >> } >> >> #ifdef CONFIG_KGDB > > Maybe like so? > > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -2206,15 +2206,14 @@ EXPORT_PER_CPU_SYMBOL(__stack_chk_guard) > > static void initialize_debug_regs(void) > { > - int i; > - > - /* Control register first */ > + /* Control register first -- to make sure everything is disabled. */ > set_debugreg(0, 7); > set_debugreg(DR6_RESERVED, 6); > - > - /* Ignore db4, db5 */ > - for (i = 0; i < 4; i++) > - set_debugreg(0, i); > + /* dr5 and dr4 don't exist */ > + set_debugreg(0, 3); > + set_debugreg(0, 2); > + set_debugreg(0, 1); > + set_debugreg(0, 0); > } > > #ifdef CONFIG_KGDB Yeah, I think it makes sense to make the change. Thanks! Xin