From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793791351; b=1VVLCddYlzzJrzCrvPExHhdY/FGoPP3C5QEkSPufVJrE/NSi8Tp7eM+yW9FCr4c++ZHd JlIpmnG2suw33T/oW9mrYEk+Pv1OPwF6ydjnf3jd0mkQk+vDmI7hMXEeq+83pn/E0QIE1 UWrgvNijXShmMzaoe/XSy+fG+dAZJpnbdgUlQBwWl+M8u0eV9tfrdv7uFO9aIZPc2mhxs wZsiM7hcRyRB0PPNscDLO0OnMUpBlN3CGi38mFeEcR51B/FObqZHVGdGgiId1eqePkSQT BrEmnvCabg9IO14X7zBrYkNMYUbephAxmTArmrg6IG8J8hn5J7szMEBoP/phk6kPU4A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793791351; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=PhlIWW6g3N+AFu1LsfAztQ3Wt3gvl8nW98AXZASgM/A=; b=ehO4OGuetP5NxGnS1z0oPGvGCe8zdsH16STFI+WUOwxMiMcX5FBS/GgPthTcwN2kNXvI FlIXmnsJKBv2AqaRNB7OZ6+9gD8FzOpsdzpFmaiBpYAaB3AenQ8A1M31ofeFjz59/OYxM 2cuXdpt3ZqnDPArAGNV7Rx13411jqjbDp55RvGeVfvhKjeA1Ea9qNRtqx5JVwQ0/FtNOt 8MmUEAKTEw5c9ZQ+kDBEs81lUv5MwBj5UdmV2LRI/HoNt4PLpffyVYEF+6f4Qjc8ZHNGA ejmEYkBAbddEf4vAn+eCyuA7mzBELOQVMEKaaQnAUKod8Af6oGpAtfyiFgXFPNGiZLQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PzQFw0Fc; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0DA43606A326 for ; Wed, 4 Nov 2026 11:22:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PzQFw0Fc Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC30B1F00A16; Wed, 4 Nov 2026 11:22:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793791350; bh=PhlIWW6g3N+AFu1LsfAztQ3Wt3gvl8nW98AXZASgM/A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=PzQFw0FctCGUG1qHhQ27pa7aqyd7BxJUFvbnrW/uv19RT1NEp+QBsPx9tWUT0MRKZ EP/IgnjNU2qQXaN6ydBSAjnVmbibh1JigkN4pF0k4b4TVFlN6vXgsHaMIv4OLWjbtW 9JZAxCVdX8vntYR8F2GsWdf0v+5nIZntQeHoeycoXS6Lh2ud8VSmqn3XOp3F5vl6Gk 1UEiBKOXa+yKIeI0dmRVCCjCuoSXB1eQLxtei9hnz4GTO95SjGcSospGRBVSQlJ3qW ekL/wjVM9kPF4GBBy0057j6cy9SYv1Kl52peqE0i5VtsYdAP5nRfejwHQD75bTPkD2 5zQx0FPWv/hpg== Date: Wed, 4 Nov 2026 13:22:22 +0200 From: Mike Rapoport To: Pasha Tatashin Cc: Pratyush Yadav , Alexander Graf , Andrew Morton , Chen Pei , George Guo , Kexin Liu , Sourabh Jain , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/2] kho: skip zero-sized lowmem and global bootmem areas Message-ID: References: <20261103-kho-bootmem-sizing-v1-0-45aa74098f34@kernel.org> <20261103-kho-bootmem-sizing-v1-1-45aa74098f34@kernel.org> 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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Nov 03, 2026 at 02:48:36PM -0500, Pasha Tatashin wrote: > On 11-03 13:49, Mike Rapoport (Microsoft) wrote: > > The lowmem and the global bootmem areas can have zero size, for example > > when none or all of the memory is below ARCH_LOW_ADDRESS_LIMIT, or when > > either of those areas is explicitly set to zero with kho_bootmem=. > > > > For a zero-sized allocation memblock returns an address without reserving > > anything, and that empty area is recorded in kho_bootmem. If there is no > > memory below ARCH_LOW_ADDRESS_LIMIT, allocation of the empty lowmem area > > fails and KHO gets disabled. > > > > Extract a helper that checks for zero size and allocates memory from > > memblock, and use it to skip empty areas the same way as empty per-node > > areas are skipped. > > > > Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers") > > Reported-by: Chen Pei > > Closes: https://lore.kernel.org/all/20261026131851.9942-1-cp0613@linux.alibaba.com > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > kernel/liveupdate/kexec_handover.c | 61 ++++++++++++++++++-------------------- > > 1 file changed, 29 insertions(+), 32 deletions(-) > > > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > > index 6f1f55fe31819..f268c57413a7e 100644 > > --- a/kernel/liveupdate/kexec_handover.c > > +++ b/kernel/liveupdate/kexec_handover.c > > @@ -820,6 +820,27 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size) > > return false; > > } > > > > +static int __init kho_reserve_bootmem_area(int *idx, phys_addr_t size, > > + phys_addr_t end, int nid) > > +{ > > + phys_addr_t addr; > > + int i = *idx; > > + > > + if (!size) > > + return 0; > > + > > + addr = memblock_alloc_range_nid(size, BOOTMEM_ALIGNMENT_BYTES, 0, end, > > + nid, true); > > + if (!addr) > > + return -ENOMEM; > > + > > + kho_bootmem[i].addr = addr; > > + kho_bootmem[i].size = size; > > + *idx = i + 1; > > + > > + return 0; > > +} > > + > > /** > > * kho_reserve_bootmem - Reserve a contiguous chunk of memory for kexec > > * > > @@ -832,7 +853,7 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size) > > static void __init kho_reserve_bootmem(void) > > { > > int nid, i = 0, max_nr_bootmem; > > - phys_addr_t addr, size; > > + phys_addr_t size; > > > > if (!kho_enable) > > return; > > @@ -852,56 +873,32 @@ static void __init kho_reserve_bootmem(void) > > * reserve bootmem area in low memory for lowmem allocations in the > > * next kernel > > */ > > - size = bootmem_size_lowmem; > > - addr = memblock_phys_alloc_range(size, BOOTMEM_ALIGNMENT_BYTES, 0, > > - ARCH_LOW_ADDRESS_LIMIT); > > - if (!addr) { > > + if (kho_reserve_bootmem_area(&i, bootmem_size_lowmem, > > + ARCH_LOW_ADDRESS_LIMIT, NUMA_NO_NODE)) { > > pr_err("Failed to reserve lowmem bootmem\n"); > > You are adding a helper that returns an error code and then ignoring it > at all call sites. Even though it can only return -ENOMEM right now, > dropping the return value is not good practice. I don't think error code is important here. Even if some theoretical future update will change kho_reserve_bootmem_area() to return anything but -ENOMEM I don't see why the error code should be printed at all. And anyway, that would be the part of that change. -- Sincerely yours, Mike.