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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 21E76F3C24E for ; Mon, 9 Mar 2026 13:42:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8BA1C6B0089; Mon, 9 Mar 2026 09:42:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 89B596B0098; Mon, 9 Mar 2026 09:42:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 773AD6B0099; Mon, 9 Mar 2026 09:42:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 67CF66B0089 for ; Mon, 9 Mar 2026 09:42:50 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 2E6FD1A0119 for ; Mon, 9 Mar 2026 13:42:50 +0000 (UTC) X-FDA: 84526640100.23.652FAD3 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) by imf11.hostedemail.com (Postfix) with ESMTP id 54E8F40007 for ; Mon, 9 Mar 2026 13:42:48 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=QnXvFd2E ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773063768; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=O7Ml/vJyi0FRJgghGtQCc2586RzghnjwSv1hQiNW19c=; b=dwmz0lg9K89FHMl0MhIVwFZx3VoJFiyBW+jYbl5GRNiTcCQ4me/ZOFlZNpSlNMzkOibCGJ w5N1FRSuhyx80r0PTBUAHEKI8SsGdn864oejc/utj6TkAe8Oi1c5uXdSsk6NUzpQRrm8AH 98bSQYolVU6kfUL+tYDdpqAnWXTbFQ8= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=debian.org header.s=smtpauto.stravinsky header.b=QnXvFd2E; spf=none (imf11.hostedemail.com: domain of leitao@debian.org has no SPF policy when checking 82.195.75.108) smtp.mailfrom=leitao@debian.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773063768; a=rsa-sha256; cv=none; b=UgXFSlLM/wMf7noL2/heASDa+iwCni1HUXCP7SQodk3vQkAbpnqQwhPwn176P7rBvGMhSE lFg/tp8fUilTaE0Rd/DWHXSk2tRzhXrDxm/bam+F4RHrxULyJJBQ5SR+ZCWi8XXOdl6knW G3gzVcIY9zJyhsn2UUU5PzEZ/iWQjIE= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:Cc:To:In-Reply-To:References: Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description; bh=O7Ml/vJyi0FRJgghGtQCc2586RzghnjwSv1hQiNW19c=; b=QnXvFd2Et5S90TK4Ts/A++2Ztl Cn/VR9gXgY/yUvfvqBzs6m7idnfnCuJpz9xk1huJY677VCStJcKu3lGhGjGPYntaChOsBlxa0KkK3 lq4feo/BjeHAMPAzBVwhmn6M4jCiBDGDZagI83LFOx90LaVIemMdN4DdP8zB+H0RDceNcJPzpjNcI Tebz/53FVEPqzrgkcNKeiKGnwt4krm7LfX5+X5WciPzDX0JEr+gwI8N3lad5FNMCTAdqboaikDpWn qKkK1CYSwBT5bOPFTETm8PmaVYQRcDqoVVKGd6flSNNmaa56En8XONgahWyMIJodab1IiJQ0+/Fp7 IGgthkzA==; Received: from authenticated user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.94.2) (envelope-from ) id 1vzasa-002G4H-Nw; Mon, 09 Mar 2026 13:42:41 +0000 From: Breno Leitao Date: Mon, 09 Mar 2026 06:41:49 -0700 Subject: [PATCH v8 6/6] kho: document kexec-metadata tracking feature MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260309-kho-v8-6-c3abcf4ac750@debian.org> References: <20260309-kho-v8-0-c3abcf4ac750@debian.org> In-Reply-To: <20260309-kho-v8-0-c3abcf4ac750@debian.org> To: Alexander Graf , Mike Rapoport , Pasha Tatashin , Pratyush Yadav Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, usamaarif642@gmail.com, Breno Leitao , SeongJae Park , kernel-team@meta.com X-Mailer: b4 0.15-dev-363b9 X-Developer-Signature: v=1; a=openpgp-sha256; l=2486; i=leitao@debian.org; h=from:subject:message-id; bh=GuS2S3Wn71jXKGx9RIpG1q7JVYnitQ1EXkky0LyglZk=; b=owEBbQKS/ZANAwAIATWjk5/8eHdtAcsmYgBprs4ze/rUp861RrV5t62pTbJLJtbdntrR9AyI8 qkmZylG1YeJAjMEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCaa7OMwAKCRA1o5Of/Hh3 bZgPD/4v3Yod2PPxx34KIn9K3RWl7jTuWUrsFK1hW5GuknLIksUYSy1hNqVshjLJL0tJFoK3wbK Vtx8cP6mtyX6+bJqGT38vExtFo2tWIe/55xDb6xyYSFvL4b+tj3K3+A6nHr4S+5Pq94JzrFg99V NXoqxOcxj46lsy5L5BHNIABY5rDqSuHF84zlo/2CJ+7pMUrS25J5mMwyPpbbWBQuRZLk7JS190/ k6Uqk0QxlwagjSHgnnjKNxib/DwMW76TD67dadJv4hzW4JKA+zZvfKYG+wvfPs9dDdDb8ydbMHy sPol8dSYkjkF8rrvyXAFuzX3FMjQ8tmxTZInP/oXcwhfYGKDaUgYKb20OKL1CwkEUHZfOxlqIUx tlEPhKfp3oCZuYTt+HIQqeXLLNbIxRUdcAAag4DjWGdHgYnwbvrF35b1NZyDN7s0bCMAEb3mHQ/ OH8tyo88JiSVeNtJcd7fHF6i6L9B3jxJY953cHHLrHlYOpFJKe5QEO4kZ82UEiP7F5vjAOC82w3 Ce7XCPByc1m/rvbfXZnpIalWvsCeDzgO/XgUO/mNL7PVsHabR18OWb8DkeaBqsOg5xZ4Bz4v1dT /j6A+KxuQ8FbDrNLwb3mInMqwr2JH+L2rHio50MXWAPzeFhnPGkMnSSGknAarZQp+tpypF8BbJi 1Z9KvPbhp3tRUEw== X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D X-Debian-User: leitao X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 54E8F40007 X-Stat-Signature: 86u9cb7ead1p6kopt3a8tt1zwj38zkgh X-Rspam-User: X-HE-Tag: 1773063768-385196 X-HE-Meta: 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 OifDDGsM FJOABh2CnCMT0S4ekFhM6a2wTzS1JQZPXomL3dpO0vhJ3INUhHQeqgOVoU64U6k6ZzdL4c8Ml67f1Grn9sFJMyWn77XnE86coK2+fO00VaMWFUkilWkxh03LVOwVli1kfRNW60rJEOzNkr0OsVx5ckkWr6q/U7zodxjhNXpQGP86IrupWwLl7hinlQQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add documentation for the kexec-metadata feature that tracks the previous kernel version and kexec boot count across kexec reboots. This helps diagnose bugs that only reproduce when kexecing from specific kernel versions. Suggested-by: Mike Rapoport Reviewed-by: Mike Rapoport (Microsoft) Signed-off-by: Breno Leitao --- Documentation/admin-guide/mm/kho.rst | 39 ++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/Documentation/admin-guide/mm/kho.rst b/Documentation/admin-guide/mm/kho.rst index 6a4ddf3440465..2c26e560bd78a 100644 --- a/Documentation/admin-guide/mm/kho.rst +++ b/Documentation/admin-guide/mm/kho.rst @@ -42,6 +42,45 @@ For example, if you used ``reserve_mem`` command line parameter to create an early memory reservation, the new kernel will have that memory at the same physical address as the old kernel. +Kexec Metadata +============== + +KHO automatically tracks metadata about the kexec chain, passing information +about the previous kernel to the next kernel. This feature helps diagnose +bugs that only reproduce when kexecing from specific kernel versions. + +On each KHO kexec, the kernel logs the previous kernel's version and the +number of kexec reboots since the last cold boot:: + + [ 0.000000] KHO: exec from: 6.19.0-rc4-next-20260107 (count 1) + +The metadata includes: + +``previous_release`` + The kernel version string (from ``uname -r``) of the kernel that + initiated the kexec. + +``kexec_count`` + The number of kexec boots since the last cold boot. On cold boot, + this counter starts at 0 and increments with each kexec. This helps + identify issues that only manifest after multiple consecutive kexec + reboots. + +Use Cases +--------- + +This metadata is particularly useful for debugging kexec transition bugs, +where a buggy kernel kexecs into a new kernel and the bug manifests only +in the second kernel. Examples of such bugs include: + +- Memory corruption from the previous kernel affecting the new kernel +- Incorrect hardware state left by the previous kernel +- Firmware/ACPI state issues that only appear in kexec scenarios + +At scale, correlating crashes to the previous kernel version enables +faster root cause analysis when issues only occur in specific kernel +transition scenarios. + debugfs Interfaces ================== -- 2.47.3