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 C7623C35FF6 for ; Thu, 13 Mar 2025 18:53:11 +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:MIME-Version:Content-Type: References:In-Reply-To:Date:Cc:To:From:Subject:Message-ID: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=R+6TXmpQQr1smtkdg3jjiiOUU23YO7K/+AmImGT4WPY=; b=xGQ3OhBcIt6ojeqcGnMiEGL7BW Et+/LyFHMZ9xefIlnmRgWWdPU5epYuKLF+C0Pfte6bf3FtYoEmpuqNm3+CQb90AJeEUySUPdQnjhw jeiMSQsmPIF9j49FShl9a+Pon6mvNvIvJeE+Zd4Hcsf6qALPRrhbWwcJU5qlr6elFWjiE/SJlHaDS wXf8ljXuXPC7PEhDbM65TJENws3IIrRsdshA30Q1awFWPOT3gx2x/f4YBSh98kk1HX/N1ezIczIe8 qac7Cw/q0WP501uC+Sy81jrGJRL2Ul7wtNBTsO+0yTOC33e7uXaVj219GI6kHSb/0YVWW/C9nvLwn 7gg2GuPw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tsng6-0000000CEsQ-1fdK; Thu, 13 Mar 2025 18:53:10 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tsnS6-0000000CDH3-2EPr for kexec@bombadil.infradead.org; Thu, 13 Mar 2025 18:38:42 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=R+6TXmpQQr1smtkdg3jjiiOUU23YO7K/+AmImGT4WPY=; b=eZcbWLAfTLq5W8s5BTHUXfGs6N OHzbCqdboaFUadQsVEUK6GbxdOHjzy2FkTUKSgtk2D4PFq7K2JAl06UDtbdYODUA5W7SjLEIjmnut YG/L+3cgBbp1B4IhVkeLGHpW3luJMZDA/YowVkMWH16ucFcj0cfYVqpGHlG89EXzlH1XXL/g/kvAP JjbOZE7FbgWtij8kYiusEGlraYLyDt2R/MSLVspA1afrsfQFpuWRZQOjQZWPAQQboLAJuLdNqbjWW oEYZaqC/k8eU/r8ecmP1CKcDWxveLtZEXtqo5kK4TNszUq0uxGdOi3W4IgN/OC3F0/2V9QqMGmP6U 2+zldIuA==; Received: from [172.31.31.145] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tsnS2-00000002mdR-1WbO; Thu, 13 Mar 2025 18:38:38 +0000 Message-ID: <8d9253eda0fd74595db05eb3449ccc5be2f563be.camel@infradead.org> Subject: Re: [PATCH v7 7/8] [DO NOT MERGE] x86/kexec: Add int3 in kexec path for testing From: David Woodhouse To: Ingo Molnar Cc: kexec@lists.infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , "Kirill A . Shutemov" , Kai Huang , Nikolay Borisov , linux-kernel@vger.kernel.org, Simon Horman , Dave Young , Peter Zijlstra , jpoimboe@kernel.org, bsz@amazon.de Date: Thu, 13 Mar 2025 18:38:38 +0000 In-Reply-To: References: <20250312144257.2348250-1-dwmw2@infradead.org> <20250312144257.2348250-8-dwmw2@infradead.org> <0CDE8ED7-D8D2-4053-AE4B-4CFF59DB56F7@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-cMsUoNzWHQXVIuwFJn1s" User-Agent: Evolution 3.52.3-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html 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 --=-cMsUoNzWHQXVIuwFJn1s Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-03-13 at 18:06 +0100, Ingo Molnar wrote: >=20 > * David Woodhouse wrote: >=20 > > The exception handler already returns if the exception was int3, but= =20 > > 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. > >=20 > > I'm less keen on making it unconditional though. Kexec is a=20 > > performance-critical path when every millisecond is perceived as=20 > > guest steal time, and the serial output should only happen in=20 > > production if something goes *wrong*. > >=20 > > And besides, most kexec users don't have early_printk enabled anyway= =20 > > so if we break them, this idea doesn't help. >=20 > So this check would only cause any real overhead if serial debugging is= =20 > enabled - in which case there's already substantial overhead due to the= =20 > serial console overhead (virtual or otherwise). > > As to not printing anything unless the early serial console is enabled= =20 > - that's fine, we'd still *break* if something doesn't work in this=20 > code path, so at least the exception handling machinery is kept=20 > well-tested. :-) I suppose so, although it's also fairly easy to test by adding an int3 into a kexec-jump test case like http://david.woodhou.se/loadret.c But yeah, it's easy enough to make the int3 register dump a little less scary and then remove the 'DO NOT MERGE' tag from the commit which adds the unconditional int3. I'm still trying to chase down the new objtool warning you noted (which I swear I saw once but now can't reproduce), and I note I need to make the early_printk hooks depend on (KEXEC_CORE && X86_64) since I removed the separate KEXEC_DEBUG option and made it all unconditional. --=-cMsUoNzWHQXVIuwFJn1s Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et 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