[PATCH v2 01/20] arm64: percpu: Fix this_cpu_write() casting

[Mark Rutland <mark.rutland@arm.com>]

The arm64 implementation of this_cpu_write() casts 'val' to unsigned
long. This is necessary to handle cases where 'val' is a pointer type,
and to avoid spurious compiler warnings for the (unreachable!) cases
where the pointer type would be cast to a smaller integer type.

Unfortunately, the cast is applied to 'val' rather than '(val)', which
won't always generate the expected value when 'val' is an expression.

For example, for this_cpu_write(pcp, zero - 1), where 'pcp' is a u64 and
'zero' is a u32:

* 'zero'                      ===> (u32) 0x00000000
* 'zero - 1'                  ===> (u32) 0xffffffff
* '(unsigned long)zero - 1'   ===> (u64) 0xffffffffffffffff
* '(unsigned long)(zero - 1)' ===> (u64) 0x00000000ffffffff

Fix this by adding brackets around 'val'

The bug described above can be seen from the disassembly of the
following test code:

| void this_cpu_write_zero_minus_1(u64 __percpu *pcp)
| {
| 	u32 zero = 0;
| 	this_cpu_write(*pcp, zero - 1);
| }
|
| void this_cpu_write_zero_minus_1_brackets(u64 __percpu *pcp)
| {
| 	u32 zero = 0;
| 	this_cpu_write(*pcp, (zero - 1));
| }

Generated code before this patch:

| <this_cpu_write_zero_minus_1>:
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mrs     x1, sp_el0
|        mov     x29, sp
|        ldr     w2, [x1, #8]
|        add     w2, w2, #0x1
|        str     w2, [x1, #8]
|        mov     x3, #0xffffffffffffffff
|        mrs     x2, tpidr_el1
|        str     x3, [x0, x2]
|        ldr     x0, [x1, #8]
|        add     x0, x0, x3
|        str     w0, [x1, #8]
|        cbz     x0, 1f
|        ldr     x0, [x1, #8]
|        cbnz    x0, 2f
| 1:     bl      preempt_schedule_notrace
| 2:     ldp     x29, x30, [sp], #16
|        autiasp
|        ret
|
| <this_cpu_write_zero_minus_1_brackets>:
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mrs     x1, sp_el0
|        mov     x29, sp
|        ldr     w2, [x1, #8]
|        add     w2, w2, #0x1
|        str     w2, [x1, #8]
|        mov     x3, #0xffffffff
|        mrs     x2, tpidr_el1
|        str     x3, [x0, x2]
|        ldr     x0, [x1, #8]
|        sub     x0, x0, #0x1
|        str     w0, [x1, #8]
|        cbz     x0, 1f
|        ldr     x0, [x1, #8]
|        cbnz    x0, 2f
| 1:     bl      preempt_schedule_notrace
| 2:     ldp     x29, x30, [sp], #16
|        autiasp
|        ret

Generated code after this patch:

| <this_cpu_write_zero_minus_1>:
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mrs     x1, sp_el0
|        mov     x29, sp
|        ldr     w2, [x1, #8]
|        add     w2, w2, #0x1
|        str     w2, [x1, #8]
|        mov     x3, #0xffffffff
|        mrs     x2, tpidr_el1
|        str     x3, [x0, x2]
|        ldr     x0, [x1, #8]
|        sub     x0, x0, #0x1
|        str     w0, [x1, #8]
|        cbz     x0, 1f
|        ldr     x0, [x1, #8]
|        cbnz    x0, 2f
| 1:     bl      preempt_schedule_notrace
| 2:     ldp     x29, x30, [sp], #16
|        autiasp
|        ret
|
| <this_cpu_write_zero_minus_1_brackets>:
|        b       this_cpu_write_zero_minus_1

Fixes: 959bf2fd03b5 ("arm64: percpu: Rewrite per-cpu ops to allow use of LSE atomics")
Reported-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Jinjie Ruan <ruanjinjie@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: stable@vger.kernel.org
---
 arch/arm64/include/asm/percpu.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
index b57b2bb009677..63bbfd4944a37 100644
--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -179,13 +179,13 @@ PERCPU_RET_OP(add, add, ldadd)
 	_pcp_protect_return(__percpu_read_64, pcp)
 
 #define this_cpu_write_1(pcp, val)	\
-	_pcp_protect(__percpu_write_8, pcp, (unsigned long)val)
+	_pcp_protect(__percpu_write_8, pcp, (unsigned long)(val))
 #define this_cpu_write_2(pcp, val)	\
-	_pcp_protect(__percpu_write_16, pcp, (unsigned long)val)
+	_pcp_protect(__percpu_write_16, pcp, (unsigned long)(val))
 #define this_cpu_write_4(pcp, val)	\
-	_pcp_protect(__percpu_write_32, pcp, (unsigned long)val)
+	_pcp_protect(__percpu_write_32, pcp, (unsigned long)(val))
 #define this_cpu_write_8(pcp, val)	\
-	_pcp_protect(__percpu_write_64, pcp, (unsigned long)val)
+	_pcp_protect(__percpu_write_64, pcp, (unsigned long)(val))
 
 #define this_cpu_add_1(pcp, val)	\
 	_pcp_protect(__percpu_add_case_8, pcp, val)
-- 
2.30.2