From: Sang-Heon Jeon Date: Sun, 3 May 2026 08:42:25 +0000 (+0900) Subject: mm/hugetlb_cma: restrict hugetlb_cma parameter to gigantic-page alignment X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fb95c50921f0a65ef9fd734ae712e416db949d91;p=thirdparty%2Flinux.git mm/hugetlb_cma: restrict hugetlb_cma parameter to gigantic-page alignment Existing hugetlb_cma parameter handling logic rejects sizes smaller than one gigantic page, but rounds up larger sizes that are not a multiple of it. The two behaviors are inconsistent and neither is documented. To remove existing inconsistent and undefined behavior, restrict hugetlb_cma parameter to only accept multiples of the gigantic page size. After this restriction, the redundant round_up() in the allocation loop can be removed. The new restriction is also documented in kernel-parameters.txt. Also, including other minor changes for readability improvement with no functional change. Link: https://lore.kernel.org/20260503084225.415980-1-ekffu200098@gmail.com Signed-off-by: Sang-Heon Jeon Suggested-by: Muchun Song Acked-by: Muchun Song Acked-by: Oscar Salvador Cc: David Hildenbrand Signed-off-by: Andrew Morton --- diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 4d0f545fb3ec..23be2f64439c 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2100,6 +2100,10 @@ Kernel parameters Format: nn[KMGTPE] or (node format) :nn[KMGTPE][,:nn[KMGTPE]] + The size must be a multiple of the gigantic page size. + When using node format, this applies to each per-node size. + Missaligned values are dropped with a warning. + Reserve a CMA area of given size and allocate gigantic hugepages using the CMA allocator. If enabled, the boot-time allocation of gigantic hugepages is skipped. diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c index 7693ccefd0c6..39344d6c78d8 100644 --- a/mm/hugetlb_cma.c +++ b/mm/hugetlb_cma.c @@ -142,7 +142,7 @@ unsigned int __weak arch_hugetlb_cma_order(void) void __init hugetlb_cma_reserve(void) { - unsigned long size, reserved, per_node, order; + unsigned long size, reserved, per_node, order, gigantic_page_size; bool node_specific_cma_alloc = false; int nid; @@ -162,37 +162,36 @@ void __init hugetlb_cma_reserve(void) * breaking this assumption. */ VM_WARN_ON(order <= MAX_PAGE_ORDER); + gigantic_page_size = PAGE_SIZE << order; hugetlb_bootmem_set_nodes(); for (nid = 0; nid < MAX_NUMNODES; nid++) { - if (hugetlb_cma_size_in_node[nid] == 0) + size = hugetlb_cma_size_in_node[nid]; + if (size == 0) continue; if (!node_isset(nid, hugetlb_bootmem_nodes)) { pr_warn("hugetlb_cma: invalid node %d specified\n", nid); - hugetlb_cma_size -= hugetlb_cma_size_in_node[nid]; - hugetlb_cma_size_in_node[nid] = 0; - continue; - } - - if (hugetlb_cma_size_in_node[nid] < (PAGE_SIZE << order)) { - pr_warn("hugetlb_cma: cma area of node %d should be at least %lu MiB\n", - nid, (PAGE_SIZE << order) / SZ_1M); - hugetlb_cma_size -= hugetlb_cma_size_in_node[nid]; - hugetlb_cma_size_in_node[nid] = 0; + } else if (!IS_ALIGNED(size, gigantic_page_size)) { + pr_warn("hugetlb_cma: cma area of node %d must be a multiple of %lu MiB\n", + nid, gigantic_page_size / SZ_1M); } else { node_specific_cma_alloc = true; + continue; } + + hugetlb_cma_size -= size; + hugetlb_cma_size_in_node[nid] = 0; } /* Validate the CMA size again in case some invalid nodes specified. */ if (!hugetlb_cma_size) return; - if (hugetlb_cma_size < (PAGE_SIZE << order)) { - pr_warn("hugetlb_cma: cma area should be at least %lu MiB\n", - (PAGE_SIZE << order) / SZ_1M); + if (!IS_ALIGNED(hugetlb_cma_size, gigantic_page_size)) { + pr_warn("hugetlb_cma: cma area must be a multiple of %lu MiB\n", + gigantic_page_size / SZ_1M); hugetlb_cma_size = 0; return; } @@ -204,7 +203,7 @@ void __init hugetlb_cma_reserve(void) */ per_node = DIV_ROUND_UP(hugetlb_cma_size, nodes_weight(hugetlb_bootmem_nodes)); - per_node = round_up(per_node, PAGE_SIZE << order); + per_node = round_up(per_node, gigantic_page_size); pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n", hugetlb_cma_size / SZ_1M, per_node / SZ_1M); } @@ -223,15 +222,13 @@ void __init hugetlb_cma_reserve(void) size = min(per_node, hugetlb_cma_size - reserved); } - size = round_up(size, PAGE_SIZE << order); - snprintf(name, sizeof(name), "hugetlb%d", nid); /* * Note that 'order per bit' is based on smallest size that * may be returned to CMA allocator in the case of * huge page demotion. */ - res = cma_declare_contiguous_multi(size, PAGE_SIZE << order, + res = cma_declare_contiguous_multi(size, gigantic_page_size, HUGETLB_PAGE_ORDER, name, &hugetlb_cma[nid], nid); if (res) {