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Message-Id: <20250611151154.46362-7-yeoreum.yun@arm.com>
Date: Wed, 11 Jun 2025 16:11:54 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: catalin.marinas@....com,
will@...nel.org,
broonie@...nel.org,
maz@...nel.org,
oliver.upton@...ux.dev,
ardb@...nel.org,
frederic@...nel.org,
james.morse@....com,
joey.gouly@....com,
scott@...amperecomputing.com
Cc: linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org,
Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH v2 6/6] arm64/futex: support futex with FEAT_LSUI
Since Armv9.6, FEAT_LSUI supplies load/store unprevileged instructions
for kernel to access user memory without clearing PSTATE.PAN.
This patch makes futex use futex_atomic operations implemented with these
instruction when cpu supports FEAT_LSUI otherwise they work with
ldxr/stlxr with clearing PSTATE.PAN bit.
Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
arch/arm64/include/asm/futex.h | 99 +++++++++++-----------------------
1 file changed, 31 insertions(+), 68 deletions(-)
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index bc06691d2062..ed4586776655 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -9,71 +9,60 @@
#include <linux/uaccess.h>
#include <asm/errno.h>
+#include <asm/lsui.h>
-#define FUTEX_MAX_LOOPS 128 /* What's the largest number you can think of? */
-
-#define __futex_atomic_op(insn, ret, oldval, uaddr, tmp, oparg) \
-do { \
- unsigned int loops = FUTEX_MAX_LOOPS; \
- \
- uaccess_enable_privileged(); \
- asm volatile( \
-" prfm pstl1strm, %2\n" \
-"1: ldxr %w1, %2\n" \
- insn "\n" \
-"2: stlxr %w0, %w3, %2\n" \
-" cbz %w0, 3f\n" \
-" sub %w4, %w4, %w0\n" \
-" cbnz %w4, 1b\n" \
-" mov %w0, %w6\n" \
-"3:\n" \
-" dmb ish\n" \
- _ASM_EXTABLE_UACCESS_ERR(1b, 3b, %w0) \
- _ASM_EXTABLE_UACCESS_ERR(2b, 3b, %w0) \
- : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp), \
- "+r" (loops) \
- : "r" (oparg), "Ir" (-EAGAIN) \
- : "memory"); \
- uaccess_disable_privileged(); \
-} while (0)
+#define FUTEX_ATOMIC_OP(op) \
+static __always_inline int \
+__futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval) \
+{ \
+ return __lsui_ll_sc_u_body(futex_atomic_##op, oparg, uaddr, oval); \
+}
+
+FUTEX_ATOMIC_OP(add)
+FUTEX_ATOMIC_OP(or)
+FUTEX_ATOMIC_OP(and)
+FUTEX_ATOMIC_OP(eor)
+FUTEX_ATOMIC_OP(set)
+
+#undef FUTEX_ATOMIC_OP
+
+static __always_inline int
+__futex_cmpxchg(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval)
+{
+ return __lsui_ll_sc_u_body(futex_cmpxchg, uaddr, oldval, newval, oval);
+}
static inline int
arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *_uaddr)
{
- int oldval = 0, ret, tmp;
- u32 __user *uaddr = __uaccess_mask_ptr(_uaddr);
+ int ret;
+ u32 __user *uaddr;
if (!access_ok(_uaddr, sizeof(u32)))
return -EFAULT;
+ uaddr = __uaccess_mask_ptr(_uaddr);
+
switch (op) {
case FUTEX_OP_SET:
- __futex_atomic_op("mov %w3, %w5",
- ret, oldval, uaddr, tmp, oparg);
+ ret = __futex_atomic_set(oparg, uaddr, oval);
break;
case FUTEX_OP_ADD:
- __futex_atomic_op("add %w3, %w1, %w5",
- ret, oldval, uaddr, tmp, oparg);
+ ret = __futex_atomic_add(oparg, uaddr, oval);
break;
case FUTEX_OP_OR:
- __futex_atomic_op("orr %w3, %w1, %w5",
- ret, oldval, uaddr, tmp, oparg);
+ ret = __futex_atomic_or(oparg, uaddr, oval);
break;
case FUTEX_OP_ANDN:
- __futex_atomic_op("and %w3, %w1, %w5",
- ret, oldval, uaddr, tmp, ~oparg);
+ ret = __futex_atomic_and(~oparg, uaddr, oval);
break;
case FUTEX_OP_XOR:
- __futex_atomic_op("eor %w3, %w1, %w5",
- ret, oldval, uaddr, tmp, oparg);
+ ret = __futex_atomic_eor(oparg, uaddr, oval);
break;
default:
ret = -ENOSYS;
}
- if (!ret)
- *oval = oldval;
-
return ret;
}
@@ -81,40 +70,14 @@ static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *_uaddr,
u32 oldval, u32 newval)
{
- int ret = 0;
- unsigned int loops = FUTEX_MAX_LOOPS;
- u32 val, tmp;
u32 __user *uaddr;
if (!access_ok(_uaddr, sizeof(u32)))
return -EFAULT;
uaddr = __uaccess_mask_ptr(_uaddr);
- uaccess_enable_privileged();
- asm volatile("// futex_atomic_cmpxchg_inatomic\n"
-" prfm pstl1strm, %2\n"
-"1: ldxr %w1, %2\n"
-" sub %w3, %w1, %w5\n"
-" cbnz %w3, 4f\n"
-"2: stlxr %w3, %w6, %2\n"
-" cbz %w3, 3f\n"
-" sub %w4, %w4, %w3\n"
-" cbnz %w4, 1b\n"
-" mov %w0, %w7\n"
-"3:\n"
-" dmb ish\n"
-"4:\n"
- _ASM_EXTABLE_UACCESS_ERR(1b, 4b, %w0)
- _ASM_EXTABLE_UACCESS_ERR(2b, 4b, %w0)
- : "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp), "+r" (loops)
- : "r" (oldval), "r" (newval), "Ir" (-EAGAIN)
- : "memory");
- uaccess_disable_privileged();
-
- if (!ret)
- *uval = val;
- return ret;
+ return __futex_cmpxchg(uaddr, oldval, newval, uval);
}
#endif /* __ASM_FUTEX_H */
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
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