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bpf: Fix softlockup in arena_map_free on 64k page kernel

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On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y,
arena_htab tests cause a segmentation fault and soft lockup.
The same failure is not observed with 4k pages on aarch64.

It turns out arena_map_free() is calling
apply_to_existing_page_range() with the address returned by
bpf_arena_get_kern_vm_start().  If this address is not page-aligned
the code ends up calling apply_to_pte_range() with that unaligned
address causing soft lockup.

Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the
division by 2 in bpf_arena_get_kern_vm_start() returns
a page-aligned value.

Fixes: 317460317a ("bpf: Introduce bpf_arena.")
Reported-by: Colm Harrington <colm.harrington@oracle.com>
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/r/20250205170059.427458-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alan Maguire 2025-02-05 17:00:59 +00:00 • committed by Alexei Starovoitov
parent 5da7e15fb5
commit 517e8a7835
1 changed files with 1 additions and 1 deletions
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2
kernel/bpf/arena.c
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@ -39,7 +39,7 @@
*/
/* number of bytes addressable by LDX/STX insn with 16-bit 'off' field */
#define GUARD_SZ (1ull << sizeof_field(struct bpf_insn, off) * 8)
#define GUARD_SZ round_up(1ull << sizeof_field(struct bpf_insn, off) * 8, PAGE_SIZE << 1)
#define KERN_VM_SZ (SZ_4G + GUARD_SZ)
struct bpf_arena {