From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=148.163.156.1 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792558760; b=tVZt3vUaZ8aXDlcl13+pP56LPphA0ThGcPoVvC4ZZXeQnJkieK8ul8eyIJgvsLonwr3t GpUuuND5vGIW9tvy627eeFmZC2JQRdXru9WlnK9A7rir2TrATFS4PiHDxnGRNy4/T+24v bhJHfsrsWBhlApmZz+L842kPZRkRNc3qndwr/uuPFqZnw08QRUXMep7ZDWazbcKwctTJb guewc75rvA9mecT+dRIOjTU+sc2Yn8+7rePimp8G6YADQN+Z6ecN/K5BuA7OdVSB8+F+z x/UwmCkBJlMD8t9pFVcSkGUXBCxX2T6KsuhEl5QqKsl5Eu/6cMsmRWm1uvCuB5w3oTQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792558760; h=DMARC-Filter:Received:DKIM-Signature:Received:Received:Received: Received:Received:Received:Received:Message-ID:Date:MIME-Version: User-Agent:Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding:X-TM-AS-GCONF: X-Proofpoint-Reinject:X-Proofpoint-GUID:X-Proofpoint-Spam-Info: X-Proofpoint-Spam-Details-Enc:X-Proofpoint-ORIG-GUID: X-Authority-Analysis:X-Proofpoint-Virus-Version: X-Proofpoint-Spam-Details; bh=sfAFk4B+vei+3elSopsi8ObDtXDl01aMMTMLoHAY6zY=; b=wm8VmwopeoRldBMMu7JHHL6/zbs+0drBR5BsvnOWes9LvXdqMT/FHa2aPYxo6Te9x5XH TO9E6bKqxnAQSVvJOIWEAzfs3dBv24YvB9RG8RBfV/s4mnx9P/AJ0jHARVF0pQu4RqhDu qnP1Uhyp3k4iVDPhdIGu5N+5ObVY9B3LUwMOq5QNfjCrWmACdHUyoyHTAZjko+BvdCqJd ch4yIvAXEzMPTYlIcrUs/uQhHtCJCqAYdCupZEuI+cNipezwizvaTicN9Malidw/8yE2m w82dgWM9KTCkIR4rO1zpK9/3/Pbl9vvQGwNwjtL/Ef03Sx27Xn/yHnch26v6D+0DkWQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=cRHqsxcP; arc=none smtp.remote-ip=148.163.156.1 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A5D22606A31D for ; Wed, 21 Oct 2026 04:59:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org A5D22606A31D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=cRHqsxcP Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 69L2F1BR064986; Wed, 21 Oct 2026 04:59:01 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=sfAFk4 B+vei+3elSopsi8ObDtXDl01aMMTMLoHAY6zY=; b=cRHqsxcP5dhOrCbCl2Ls33 kA18CiwiE9c+4Fmw2XGI8JFKQduEVtf3JqDeSmZvgvMzehEvCM/LR8wRBrdUHJX+ K2EeFDwgTJTPu0slwpOcM1RMPFr1caS0wq2x8AWE4+5/24TBN7H4EjUHMVXFv6NK 9i/5Xxzoz8ucvJCStx+OTxFo+E0C97GoA1x9uAailgfQNufnIzT5RjqXNoYu6MU2 MIM7W506wPnLEnzfU4qBYSvRZ85XEKU48P5ogUtump2Et/KF430Zo2n821boCdeS aCaKtaQvZuWnCOsclQXWlUxbnrpS+DwiNUru9CdJf34cikehX0wrZYvlUapT5KPA == Received: from ppma13.dal12v.mail.ibm.com (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4hdw58q106-1 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 21 Oct 2026 04:59:00 +0000 (GMT) Received: from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1]) by ppma13.dal12v.mail.ibm.com (8.18.1.11/8.18.1.11) with ESMTP id 69L2JqUJ1230282; Wed, 21 Oct 2026 04:59:00 GMT Received: from smtprelay05.fra02v.mail.ibm.com ([9.218.2.225]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4hefss1dnj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 21 Oct 2026 04:59:00 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 69L4wuS045941058 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 21 Oct 2026 04:58:56 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3A99D20085; Wed, 21 Oct 2026 04:58:56 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B316220082; Wed, 21 Oct 2026 04:58:52 +0000 (GMT) Received: from [9.123.14.142] (unknown [9.123.14.142]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 21 Oct 2026 04:58:52 +0000 (GMT) Message-ID: <3d342c03-f12f-462d-b3c6-510f155ff267@linux.ibm.com> Date: Wed, 21 Oct 2026 10:31:27 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] kho: check scratch vs CMA alignment at runtime To: Pratyush Yadav Cc: kexec@lists.infradead.org, Aditya Gupta , Alexander Graf , Andrew Morton , Baoquan He , "Christophe Leroy (CS GROUP)" , Hari Bathini , Madhavan Srinivasan , Mahesh Salgaonkar , Michael Ellerman , Mike Rapoport , Nicholas Piggin , Pasha Tatashin , "Ritesh Harjani (IBM)" , Shivang Upadhyay , Shrikanth Hegde , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <20260928083226.107807-1-sourabhjain@linux.ibm.com> <20260928083226.107807-2-sourabhjain@linux.ibm.com> <2vxzfqybj8it.fsf@kernel.org> Content-Language: en-US From: Sourabh Jain In-Reply-To: <2vxzfqybj8it.fsf@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: aN4T9DGkggG4gTSFxpsFy0li-llBHITp X-Proofpoint-Spam-Info: AW1haW4tMjYxMDIxMDAxOCBTYWx0ZWRfX4/ekYuLP0jTS gfp9csY5GMnBqfzt50/Jn0pvXDa/D3GQiPkoyfw9lrPWTCQCTznGBLoDZKAB8z7LbHQzxOdf0UD ZdXJvkKI5gb/WQKn38y5OeTcQRu3DsA= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDIxMDAxOCBTYWx0ZWRfX5YLm0P8pI1zz RNMCP7xdAfJDzf6yT+bJ8sqjcs6HWse3K0afsDQVQAkCCAvwv+Ixqc95IjdBlLrlD7y6H8va/jH EisrwZ+tOCB4MBQribT3Ihbg3mfRHwdKCFc4X8bZwSgvKkAxo/gEtxwmmIhnoPQSQg1+pVLg0ge p1i2cfPBHjvApCj/NXfv5/7HddSbCpoeznez/Ffmy/F1xZn8B6uSluPEFydSDLHSYrLRPQU0/9P a9ZDMYfTb62gPBJIi07HTVB+rtfBKVgLQl4xRdx43mjuqqgztl9Ff3tv9QDfRV669HE2KalqMSO y0tc7po+mOHLZux8FuHF/c6SVgufpcer4Aciw5qLNWozZvW9686//g1I+1QpSm9zIE/7/pow6tW uLrfiLZXzIQIqoV3YSpb2C6i08R/VV2pmlEKHzsXGELNEkR51PlQdVXmfujpRXg7RIDVYiYMi1J D+UmGl+6+95y29KzsYA== X-Proofpoint-ORIG-GUID: 3_2FMnQbRqIzSRLEGfDujs0GFUx0wl7r X-Authority-Analysis: v=2.4 cv=Ob4NnRTY c=1 sm=1 tr=0 ts=6ad84695 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=vggBfdFIAAAA:8 a=Z4Rwk6OoAAAA:8 a=VwQbUJbxAAAA:8 a=pGLkceISAAAA:8 a=7ipKWUHlAAAA:8 a=voM4FWlXAAAA:8 a=rxpbpe3YEeMVxz9nh0AA:9 a=QEXdDO2ut3YA:10 a=HkZW87K1Qel5hWWM3VKY:22 a=gpc5p9EgBqZVLdJeV_V1:22 a=IC2XNlieTeVoXbcui8wp:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-21_01,2026-10-19_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 adultscore=0 phishscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 clxscore=1015 impostorscore=0 priorityscore=1501 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610190000 definitions=main-2610210018 On 12/10/26 20:00, Pratyush Yadav wrote: > On Mon, Sep 28 2026, Sourabh Jain wrote: > >> KHO requires the scratch alignment to be at least CMA_MIN_ALIGNMENT_BYTES, >> and this is currently enforced with a static_assert(). >> >> That assertion breaks the build on powerpc once CONFIG_KEXEC_HANDOVER is >> enabled together with CONFIG_TRANSPARENT_HUGEPAGE or CONFIG_HUGETLB_PAGE: >> >> kernel/liveupdate/kexec_handover.c:49:39: error: expression in static assertion is not constant >> 49 | static_assert(SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES); >> ./include/linux/build_bug.h:80:56: note: in definition of macro '__static_assert' >> 80 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg) >> | ^~~~ >> kernel/liveupdate/kexec_handover.c:49:1: note: in expansion of macro 'static_assert' >> 49 | static_assert(SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES); >> >> CMA_MIN_ALIGNMENT_BYTES depends on pageblock_order, which is not a >> compile-time constant with certain configs, such as >> CONFIG_HUGETLB_PAGE_SIZE_VARIABLE on powerpc. The next patch in this >> series enables KHO on powerpc, so the alignment must be checked at >> runtime instead. >> >> Replace the static_assert() with a runtime check at the start of >> kho_reserve_scratch(), before any scratch memory is reserved. If the >> scratch alignment is smaller than the CMA minimum alignment, warn once >> and disable KHO rather than continue with a misaligned reservation. >> >> Cc: Aditya Gupta >> Cc: Alexander Graf >> Cc: Andrew Morton >> Cc: Baoquan He >> Cc: Christophe Leroy (CS GROUP) >> Cc: Hari Bathini >> Cc: Madhavan Srinivasan >> Cc: Mahesh Salgaonkar >> Cc: Michael Ellerman >> Cc: Mike Rapoport >> Cc: Nicholas Piggin >> Cc: Pasha Tatashin >> Cc: Pratyush Yadav >> Cc: Ritesh Harjani (IBM) >> Cc: Shivang Upadhyay >> Cc: Shrikanth Hegde >> Cc: linux-kernel@vger.kernel.org >> Cc: linuxppc-dev@lists.ozlabs.org >> Signed-off-by: Sourabh Jain >> --- >> kernel/liveupdate/kexec_handover.c | 23 +++++++++++++++-------- >> 1 file changed, 15 insertions(+), 8 deletions(-) >> >> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c >> index 7c4d86daf86d..dc76dd6b74da 100644 >> --- a/kernel/liveupdate/kexec_handover.c >> +++ b/kernel/liveupdate/kexec_handover.c >> @@ -39,15 +39,7 @@ >> #include "../kexec_internal.h" >> #include "kexec_handover_internal.h" >> >> -/* >> - * This is the minimal alignment required by deferred struct page init. >> - * deferred_init_memmap_chunk frees memory to the buddy allocator, which looks >> - * at the neighboring pages (up to MAX_PAGE_ORDER) to merge them. >> - * If KHO scratch is not aligned to that value, buddy can access uninitialized >> - * struct pages, which can cause a crash. >> - */ >> #define SCRATCH_ALIGNMENT_BYTES (PAGE_SIZE * MAX_ORDER_NR_PAGES) >> -static_assert(SCRATCH_ALIGNMENT_BYTES >= CMA_MIN_ALIGNMENT_BYTES); >> >> /* The magic token for preserved pages */ >> #define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */ >> @@ -836,6 +828,21 @@ static void __init kho_reserve_scratch(void) >> if (!kho_enable) >> return; >> >> + /* >> + * This is the minimal alignment required by deferred struct page init. >> + * deferred_init_memmap_chunk frees memory to the buddy allocator, which looks >> + * at the neighboring pages (up to MAX_PAGE_ORDER) to merge them. >> + * If KHO scratch is not aligned to that value, buddy can access uninitialized >> + * struct pages, which can cause a crash. >> + */ >> + if (WARN_ON_ONCE(SCRATCH_ALIGNMENT_BYTES < CMA_MIN_ALIGNMENT_BYTES)) { > Nit: do we need both the WARN_ON_ONCE() and the pr_err()? Can't we drop > the WARN and keep the pr_err only? Yes pr_err is good enough. I will remove WARN_ON_ONCE()... > > LGTM otherwise. Thanks for the review. - Sourabh Jain > >> + pr_err("scratch alignment %lu < CMA minimum %lu, disabling\n", >> + (unsigned long)SCRATCH_ALIGNMENT_BYTES, >> + (unsigned long)CMA_MIN_ALIGNMENT_BYTES); >> + kho_enable = false; >> + return; >> + } >> + >> scratch_size_update(); >> >> /* FIXME: deal with node hot-plug/remove */