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authorLinus Torvalds <torvalds@linux-foundation.org>2022-04-22 11:41:38 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-04-24 10:05:38 -0700
commit9becb688913023124464c5463b4389b3b293f0e7 (patch)
tree667bbb7b930d8b35dad9c68d8ad186a3100eaecc
parentf2edd118d02dd11449b126f786f09749ca152ba5 (diff)
kvmalloc: use vmalloc_huge for vmalloc allocations
Since commit 559089e0a93d ("vmalloc: replace VM_NO_HUGE_VMAP with VM_ALLOW_HUGE_VMAP"), the use of hugepage mappings for vmalloc is an opt-in strategy, because it caused a number of problems that weren't noticed until x86 enabled it too. One of the issues was fixed by Nick Piggin in commit 3b8000ae185c ("mm/vmalloc: huge vmalloc backing pages should be split rather than compound"), but I'm still worried about page protection issues, and VM_FLUSH_RESET_PERMS in particular. However, like the hash table allocation case (commit f2edd118d02d: "page_alloc: use vmalloc_huge for large system hash"), the use of kvmalloc() should be safe from any such games, since the returned pointer might be a SLUB allocation, and as such no user should reasonably be using it in any odd ways. We also know that the allocations are fairly large, since it falls back to the vmalloc case only when a kmalloc() fails. So using a hugepage mapping seems both safe and relevant. This patch does show a weakness in the opt-in strategy: since the opt-in flag is in the 'vm_flags', not the usual gfp_t allocation flags, very few of the usual interfaces actually expose it. That's not much of an issue in this case that already used one of the fairly specialized low-level vmalloc interfaces for the allocation, but for a lot of other vmalloc() users that might want to opt in, it's going to be very inconvenient. We'll either have to fix any compatibility problems, or expose it in the gfp flags (__GFP_COMP would have made a lot of sense) to allow normal vmalloc() users to use hugepage mappings. That said, the cases that really matter were probably already taken care of by the hash tabel allocation. Link: https://lore.kernel.org/all/20220415164413.2727220-1-song@kernel.org/ Link: https://lore.kernel.org/all/CAHk-=whao=iosX1s5Z4SF-ZGa-ebAukJoAdUJFk5SPwnofV+Vg@mail.gmail.com/ Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Paul Menzel <pmenzel@molgen.mpg.de> Cc: Song Liu <songliubraving@fb.com> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/util.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/mm/util.c b/mm/util.c
index 54e5e761a9a9..3492a9e81aa3 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -592,8 +592,15 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
return NULL;
}
- return __vmalloc_node(size, 1, flags, node,
- __builtin_return_address(0));
+ /*
+ * kvmalloc() can always use VM_ALLOW_HUGE_VMAP,
+ * since the callers already cannot assume anything
+ * about the resulting pointer, and cannot play
+ * protection games.
+ */
+ return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
+ flags, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
+ node, __builtin_return_address(0));
}
EXPORT_SYMBOL(kvmalloc_node);