From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9E698C35FF6 for ; Thu, 13 Mar 2025 17:15:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=PXJ6+L6L3pDQEM5UY7CMnGVjtGIc37AUYwWjD/301wM=; b=2o8E4rQtGJ8QrQqGwh6nXn8omz q+A6CEqeZuwy0+RuGoWlXKbY358sedTlUTYbuwWx5iIv09aET/BpYtEX5icCBnOw+oVTM55kmv0Iv z9CpM1bPjo8EOkI/fOgJ2asJ8HNLOwIVbobUpMWhwsAtXWa5OjBKLCWthXBb7WpXGj7BVdFpim91+ nH1+kign9Mul6PElHoiXA6p2PCdT2L1UbWXzz/eYnZNtRmAnWjPvfUNDtIMUYeTCRJJ80fXbWaU0V 6uzTSz/Grd7JnYy+Xl3d4hnNfjKUizvcCGV6dDY/JE/+3a12xfsTOSl/la7xuqcVy02322HFosaoo 6/dHLB0w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tsm9k-0000000Bz3A-0lcF; Thu, 13 Mar 2025 17:15:40 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tsm1J-0000000BvUa-3jAd for kexec@lists.infradead.org; Thu, 13 Mar 2025 17:06:59 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 7EFD85C621E; Thu, 13 Mar 2025 17:04:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06B38C4CEDD; Thu, 13 Mar 2025 17:06:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741885617; bh=Nz9EEbxa96ubbGlmtt8GqUKsPrxRe7iBnOqLJfXPMJ4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=htfqBc1o8KoQCwCwBsyUS+lFslHdDQBvQ/yEkPjM1sTnEJcMgDfXOvgdt59jsYUcN Gmdept+WN/OWh+7QkJJMtNeolAhvIExamo2gd/8+l57Z01YE1OIUsAH3jOY3YBQabT YcdgxGAeVJZSIA/uDNdrLZCkVBhzFiXZNMwEb5M39mv1qaRft43K6seXa0/MNDxBZo F7LfgVtdZTprlAzjNezH55eTHVSSXadrSGMJ0VC9jx5ExJIfa9264HvannO42xloRg Wqc7vZ0b0ggO/jjd4XuLbA/Afq3L7KocRL3GW5Exe91i2O0Q9knH+YBxTUe33yXlcA NRNRjf3rMF+rw== Date: Thu, 13 Mar 2025 18:06:49 +0100 From: Ingo Molnar To: David Woodhouse Cc: kexec@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , David Woodhouse , "Kirill A . Shutemov" , Kai Huang , Nikolay Borisov , linux-kernel@vger.kernel.org, Simon Horman , Dave Young , Peter Zijlstra , jpoimboe@kernel.org, bsz@amazon.de Subject: Re: [PATCH v7 7/8] [DO NOT MERGE] x86/kexec: Add int3 in kexec path for testing Message-ID: References: <20250312144257.2348250-1-dwmw2@infradead.org> <20250312144257.2348250-8-dwmw2@infradead.org> <0CDE8ED7-D8D2-4053-AE4B-4CFF59DB56F7@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0CDE8ED7-D8D2-4053-AE4B-4CFF59DB56F7@infradead.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250313_100657_968059_BAD0925D X-CRM114-Status: GOOD ( 14.27 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org * David Woodhouse wrote: > The exception handler already returns if the exception was int3, but > not for anything else. Less so the "print something warm and fuzzy" > part; it just does the same register dump. But we could change that. > > I'm less keen on making it unconditional though. Kexec is a > performance-critical path when every millisecond is perceived as > guest steal time, and the serial output should only happen in > production if something goes *wrong*. > > And besides, most kexec users don't have early_printk enabled anyway > so if we break them, this idea doesn't help. So this check would only cause any real overhead if serial debugging is enabled - in which case there's already substantial overhead due to the serial console overhead (virtual or otherwise). As to not printing anything unless the early serial console is enabled - that's fine, we'd still *break* if something doesn't work in this code path, so at least the exception handling machinery is kept well-tested. :-) Thanks, Ingo