queue-7.2/bpf-riscv-make-arena-support-depend-on-zacas.patch

From 536b523b407397c8d3967c020ce7aad70a0ea030 Mon Sep 17 00:00:00 2001
From: Chen Pei <cp0613@linux.alibaba.com>
Date: Wed, 2 Sep 2026 14:14:51 +0800
Subject: bpf, riscv: Make arena support depend on ZACAS
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From: Chen Pei <cp0613@linux.alibaba.com>

commit 536b523b407397c8d3967c020ce7aad70a0ea030 upstream.

The arena range tree allocates its nodes with kmalloc_nolock() since
commit f8c67d8550ee ("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: f8c67d8550ee ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/riscv/net/bpf_jit_comp64.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -2114,7 +2114,15 @@ 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)