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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Exq5Sp7z; 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 8FE80606A31D; Fri, 30 Oct 2026 08:58:12 +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=Exq5Sp7z Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0AABA1F00A1B; Fri, 30 Oct 2026 08:58:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793350692; bh=r280hiRf1n6xtUd8PrDvA2MR0wI6dZTEfLDR+8JhqFg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Exq5Sp7zAbqNuqGv6NplKuvdr/nF4Y3VmHgtgpTLaZbU9Jx+zMmy9hxCvaaN31rRH OXAH49p1efwmh9zrCzsYf1pFWirOHcKauQ7DZ6dnzldnZcaI9rAnWgsVclPTmFxOIu wqwyFVvJv6NJhGAUPUhuQGODdeljpPlxdAz0GS6+RF7DFvAR8XjS0lo7BevGFn6/wJ mz7quZWteNXZVRLTrgNo935jT8qWHudzcdV+n3P8+A+zxNy3fWJsf+evbdLNaUs2HL QSaYI8xsJc88Guj1G+FbrjZM0Ugyi4eqJFZMlH5Wi31jHqemR78BtdXpdRcXqF0es3 ai1bGZuOgGUDg== Message-ID: <6086c386-3903-476f-ba55-bd6c21072f72@kernel.org> Date: Fri, 30 Oct 2026 09:58:05 +0100 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] mm/hugetlb_vmemmap: Fix usemap overrun on nodes with multiple ranges To: Tim Chen , Andrew Morton , Muchun Song , Oscar Salvador Cc: Frank van der Linden , Mike Rapoport , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Mohini Narkhede , Pooja Jain , Doug Nelson References: <20261029212137.3141875-1-tim.c.chen@linux.intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/29/26 22:21, Tim Chen wrote: > sparse_init_nid() allocates one usemap slot (struct mem_section_usage) > per present section in [pnum_begin, pnum_end), and > sparse_init_early_section() hands them out in order, with a BUG_ON() when > they run out. hugetlb_vmemmap_init_early(nid) however initializes the > sections of every bootmem gigantic page on the node, including pages > outside the range being initialized. If a node's memory is split into > more than one range, sparse_init() calls sparse_init_nid() once per range, > and this takes more slots than were allocated. The same happens if a > gigantic page straddles a node boundary. > > For example, with this SRAT layout every node has a small range below 4G > and a large range above 4G: > > Node 0 PXM 0 [mem 0x00000000-0x2fffffff] 768 MB (low) > Node 0 PXM 0 [mem 0x100000000-0x80cfffffff] (high) > Node 1 PXM 1 [mem 0x30000000-0x5fffffff] 768 MB (low) > ... > > In 128 MB memory sections (x86_64 SECTION_SIZE_BITS = 27), node 0's low > range is sections 0x00-0x05 (6 present sections) and its high range is > sections 0x20-0x1019. The low ranges of the other nodes are 4 or 6 > sections, all smaller than the 8 sections of a 1G page. > > Node 0's first range has 6 sections, so 6 slots. With "hugepagesz=1G > hugepages=400", hugetlb_vmemmap_init_early(0) then initializes node 0's > 1G page at 0x67c0000000 (sections 0xcf8-0xcff, in its high range), and > the 7th section hits the BUG_ON() (seen on v7.2.6): > > kernel BUG at mm/sparse.c:268! > RIP: 0010:sparse_init_early_section+0x9f/0xb0 > RAX: 0000000000200000 RBX: 0000000000000cfe RCX: 0000000000000020 > RDX: 0000000000000cfe RSI: ffd7e1d09fc00000 RDI: ff252cb28ffb3f50 > R10: ff252cb28ffb3d40 R13: 0000000000000d00 > Call Trace: > hugetlb_vmemmap_init_early+0xe1/0x140 > sparse_init_nid+0x56/0x370 > sparse_init+0x192/0x2b0 > free_area_init+0x7f/0x690 > start_kernel+0x64/0x540 > > Here RDX is the section number, and R10/RDI are 6 slots apart: the start > of the usemap buffer and its current position, which is the end. > > Pass the section range to hugetlb_vmemmap_init_early() and only pre-HVO a > page whose sections are all present and within it. Ranges are disjoint, > so each page is handled once, in its own range. > > Skipped pages are not marked HUGE_BOOTMEM_HVO. Their sections get a > regular memmap from sparse_init_nid(), and the pages are optimized later > by hugetlb_vmemmap_optimize_bootmem_folios(). > > Fixes: b1222550fbf7 ("mm/hugetlb: do pre-HVO for bootmem allocated pages") > Cc: stable@vger.kernel.org > Reported-by: Mohini Narkhede > Tested-by: Pooja Jain > Signed-off-by: Tim Chen > --- > include/linux/mmzone.h | 9 ++++++--- > mm/hugetlb_vmemmap.c | 38 ++++++++++++++++++++++++++++++++++---- > mm/hugetlb_vmemmap.h | 7 +++++-- > mm/sparse-vmemmap.c | 16 +++++++++------- > mm/sparse.c | 2 +- > 5 files changed, 55 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 94f9c3ff54160..da17dae8b057b 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -2167,13 +2167,16 @@ static inline int preinited_vmemmap_section(const struct mem_section *section) > (section->section_mem_map & SECTION_IS_VMEMMAP_PREINIT)); > } > > -void sparse_vmemmap_init_nid_early(int nid); > +void sparse_vmemmap_init_nid_early(int nid, unsigned long pnum_begin, > + unsigned long pnum_end); > #else > static inline int preinited_vmemmap_section(const struct mem_section *section) > { > return 0; > } > -static inline void sparse_vmemmap_init_nid_early(int nid) > +static inline void sparse_vmemmap_init_nid_early(int nid, > + unsigned long pnum_begin, > + unsigned long pnum_end) Two tab indent please in all cases here that you are touching, thanks. -- Cheers, David