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bpf, riscv: Make arena support depend on ZACAS

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The arena range tree allocates its nodes with kmalloc_nolock() since
commit f8c67d8550 ("bpf: Use kmalloc_nolock() in range tree").
kmalloc_nolock() requires slab caches with cmpxchg128 support
(__CMPXCHG_DOUBLE); on riscv cmpxchg128 is provided by the ZACAS
extension. On systems without ZACAS every arena map creation fails
with a misleading -ENOMEM.

Report the missing support instead: make bpf_jit_supports_arena()
return system_has_cmpxchg128() where it is defined, so arena map
creation fails with -EOPNOTSUPP on systems without ZACAS. The macro
is only defined when both CONFIG_RISCV_ISA_ZACAS and
CONFIG_TOOLCHAIN_HAS_ZACAS are enabled, so guard it with #ifdef the
same way mm/slab.h consumes it, and reject arena otherwise. This
matches how arena BPF_CMPXCHG instructions are already gated on ZACAS
in bpf_jit_supports_insn().

Fixes: f8c67d8550 ("bpf: Use kmalloc_nolock() in range tree")
Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
Acked-by: Pu Lehui <pulehui@huawei.com>
Acked-by: Björn Töpel <bjorn@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/bpf/20260902061451.1416-1-cp0613@linux.alibaba.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
This commit is contained in:
Chen Pei 2026-09-02 14:14:51 +08:00 committed by Kumar Kartikeya Dwivedi
parent fd5348b434
commit 536b523b40
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1 changed files with 9 additions and 1 deletions
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10
arch/riscv/net/bpf_jit_comp64.c
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@ -2128,7 +2128,15 @@ bool bpf_jit_supports_ptr_xchg(void)
bool bpf_jit_supports_arena(void)
{
return true;
/*
* The arena range tree uses kmalloc_nolock(), which needs
* cmpxchg128, provided by ZACAS on riscv.
*/
#ifdef system_has_cmpxchg128
return system_has_cmpxchg128();
#else
return false;
#endif
}
bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)