From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 1B1AF606B730 for ; Thu, 12 Nov 2026 08:49:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=3TPvLBuf; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=blR2ZZkc 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-Unsubscribe-Post:List-Owner; bh=OGChezwGEAs5VmxdKN/i88B/dah14lbYLutkEhF0lOY=; b=3TPvLBufgoTAntdjzhlUVmwMPn oQ6Xa0C781gb7X36JvgktD2Ax229fmXTr3jzldPN/op7xy0safgCebbrNGhl5a3LrjrMaIq3c9iiC VUq/d0vds6c8CvudlWnu4k0YhEBdg8VRcnndXQIbAwrHAmOeJNe7rHVVMxaEOwNgdDC3JIc4kQZHl v4Bbu5C28ljFTBHz174YthesftkjVsK8n6TcyHykaDtOUXazkvCMn9KZ5kOuqC8FbpnG4JXh7mCIQ Vj/Gw6+pQq6qt8xJ9KCqDROIUbPd7RAAx9nEf9tTQ8/Yo3HnEWKmT0ja5OjYt4zWjZ6mE8qA6H4+T l2z31CdQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRQVI-00000009Ef6-2iDl; Thu, 12 Nov 2026 08:49:56 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xRQVG-00000009Ee2-02u1 for kexec@lists.infradead.org; Thu, 12 Nov 2026 08:49:54 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id AE97D43645; Thu, 12 Nov 2026 08:49:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA7AE1F00A05; Thu, 12 Nov 2026 08:49:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794473393; bh=OGChezwGEAs5VmxdKN/i88B/dah14lbYLutkEhF0lOY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=blR2ZZkcc/vDDO96F1pNxo2m29Sm1eEE58wpJKJVkHYo/oXT8bnVVxwZZly5gZt9q WjKhsecawJUo7hwiLqoB1tVNvATaSKrnCQij9ms9i4j046DyigYLVgzKpPVW/Tm32u DFsGgSAhvGZFpD7jZe6hMTEs8q6xFGpoAsvodr12hfkgt1d+rnYLrT4Zo91RMnmygO 0yruuXkzYrHRiuER+joOHfZNGA23QqvNVf/8ozCvJuVQ3b+UfYkf9kKtv/5ozkNjEA SJWrIn3UVe4emvFMOq5MsjJhsAU82JyD7Ikm8arKDsaA71v1lyHUIdzvm0qEtUhFC4 NtcmR0wFZxi0g== Date: Thu, 12 Nov 2026 10:49:46 +0200 From: Mike Rapoport To: Mukesh Pilaniya Cc: Pasha Tatashin , 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 v2 1/3] kho: walk bootmem areas in address order Message-ID: References: <20261104-kho-bootmem-sizing-v2-0-b0d1a834780f@kernel.org> <20261104-kho-bootmem-sizing-v2-1-b0d1a834780f@kernel.org> <990cc079-70ab-4fcf-9974-679aaf07849e@redhat.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <990cc079-70ab-4fcf-9974-679aaf07849e@redhat.com> X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Nov 12, 2026 at 12:02:05PM +0530, Mukesh Pilaniya wrote: > Hi Mike, > > On 04/11/26 10:20 pm, Mike Rapoport (Microsoft) wrote: > > kexec_add_buffer() users may depend on the order in which memory holes are > > searched. For instance, arm64 places the kernel bottom-up and then > > requires the DTB to be above the kernel. > > > > kho_walk_bootmem() walks the bootmem areas in the order they were > > reserved, so if the kernel lands in a small area at the top of the memory > > there is no room left for the DTB and kexec fails. For example, on an > > arm64 VM with 2G of RAM and kho_bootmem=8M,64M,64M, the lowmem area is > > reserved first at the top of the memory, the kernel image takes most of > > it and kexec fails with > > > > kexec_file(Image): Could not find any suitable kernel location! > > > > Sort the bootmem areas by address and walk them in ascending order, or in > > descending order for top-down searches, like kexec_walk_resources() does. > > > > Fixes: 3bdecc3c93f9 ("kexec: add KHO support to kexec file loads") > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > kernel/liveupdate/kexec_handover.c | 57 ++++++++++++++++++++++++++++++-------- > > 1 file changed, 46 insertions(+), 11 deletions(-) > > > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > > index 6f1f55fe31819..2ac5d94f33fd4 100644 > > --- a/kernel/liveupdate/kexec_handover.c > > +++ b/kernel/liveupdate/kexec_handover.c > > @@ -26,6 +26,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > > > @@ -820,6 +821,14 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size) > > return false; > > } > > > > +static int __init kho_bootmem_cmp(const void *_a, const void *_b) > > +{ > > + const struct kho_bootmem *a = _a; > > + const struct kho_bootmem *b = _b; > > + > > + return cmp_int(a->addr, b->addr); > > +} > > + > > /** > > * kho_reserve_bootmem - Reserve a contiguous chunk of memory for kexec > > * > > @@ -904,6 +913,9 @@ static void __init kho_reserve_bootmem(void) > > */ > > kho_bootmem_cnt = i; > > > > + sort(kho_bootmem, kho_bootmem_cnt, sizeof(*kho_bootmem), > > + kho_bootmem_cmp, NULL); > This only covers the case where this kernel allocated the areas itself. > On a KHO boot the array comes from the previous kernel. A kernel with > this series that is handed over from one without it therefore keeps > walking the areas in reservation order for every following > kexec_file_load, and the arm64 failure you describe comes back until the > next cold boot and vise versa because the ABI string is still > "kho-v4". If we were able to kexec from a kernel with no reservation ordering, the issue is not there, isn't it? And after a cycle of KHO boots to newer kernels we anyway can get to the point when bootmem is not large enough. > > +static int kho_bootmem_walk_top_down(struct kexec_buf *kbuf, > > + int (*func)(struct resource *, void *)) > > { > > int ret = 0; > > - int i; > > > > - for (i = 0; i < kho_bootmem_cnt; i++) { > > - struct resource res = { > > - .start = kho_bootmem[i].addr, > > - .end = kho_bootmem[i].addr + kho_bootmem[i].size - 1, > > - }; > > + for (int i = kho_bootmem_cnt - 1; i >= 0; i--) { > > kho_bootmem_cnt is unsigned, but the reverse loops in > kho_reserve_bootmem() and kho_bootmem_walk_top_down() start an int > counter at kho_bootmem_cnt - 1, which for a zero count is UINT_MAX > converted to int. That conversion is implementation-defined; with the > current compilers it yields -1 and the loop body is skipped. We never get here with kho_bootmem_cnt == 0. > How about using this one. > for (unsigned int i = kho_bootmem_cnt; i-- > 0;) > > Reviewed-by: Mukesh Pilaniya Thanks! > -- > Regards, > Mukesh Pilaniya > -- Sincerely yours, Mike.