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authorWill Deacon <will.deacon@arm.com>2016-07-04 17:44:48 +0100
committerWill Deacon <will.deacon@arm.com>2016-10-19 15:37:29 +0100
commit1e6e57d9b34a9075d5f9e2048ea7b09756590d11 (patch)
treeb5708d14f64b03758cb18b795ef18077fdac9b55 /arch/arm64
parent1c5b51dfb7b4564008e0cadec5381a69e88b0d21 (diff)
arm64: percpu: rewrite ll/sc loops in assembly
Writing the outer loop of an LL/SC sequence using do {...} while constructs potentially allows the compiler to hoist memory accesses between the STXR and the branch back to the LDXR. On CPUs that do not guarantee forward progress of LL/SC loops when faced with memory accesses to the same ERG (up to 2k) between the failed STXR and the branch back, we may end up livelocking. This patch avoids this issue in our percpu atomics by rewriting the outer loop as part of the LL/SC inline assembly block. Cc: <stable@vger.kernel.org> Fixes: f97fc810798c ("arm64: percpu: Implement this_cpu operations") Reviewed-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/include/asm/percpu.h120
1 files changed, 56 insertions, 64 deletions
diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
index 2fee2f59288c..5394c8405e66 100644
--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -44,48 +44,44 @@ static inline unsigned long __percpu_##op(void *ptr, \
\
switch (size) { \
case 1: \
- do { \
- asm ("//__per_cpu_" #op "_1\n" \
- "ldxrb %w[ret], %[ptr]\n" \
+ asm ("//__per_cpu_" #op "_1\n" \
+ "1: ldxrb %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
- "stxrb %w[loop], %w[ret], %[ptr]\n" \
- : [loop] "=&r" (loop), [ret] "=&r" (ret), \
- [ptr] "+Q"(*(u8 *)ptr) \
- : [val] "Ir" (val)); \
- } while (loop); \
+ " stxrb %w[loop], %w[ret], %[ptr]\n" \
+ " cbnz %w[loop], 1b" \
+ : [loop] "=&r" (loop), [ret] "=&r" (ret), \
+ [ptr] "+Q"(*(u8 *)ptr) \
+ : [val] "Ir" (val)); \
break; \
case 2: \
- do { \
- asm ("//__per_cpu_" #op "_2\n" \
- "ldxrh %w[ret], %[ptr]\n" \
+ asm ("//__per_cpu_" #op "_2\n" \
+ "1: ldxrh %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
- "stxrh %w[loop], %w[ret], %[ptr]\n" \
- : [loop] "=&r" (loop), [ret] "=&r" (ret), \
- [ptr] "+Q"(*(u16 *)ptr) \
- : [val] "Ir" (val)); \
- } while (loop); \
+ " stxrh %w[loop], %w[ret], %[ptr]\n" \
+ " cbnz %w[loop], 1b" \
+ : [loop] "=&r" (loop), [ret] "=&r" (ret), \
+ [ptr] "+Q"(*(u16 *)ptr) \
+ : [val] "Ir" (val)); \
break; \
case 4: \
- do { \
- asm ("//__per_cpu_" #op "_4\n" \
- "ldxr %w[ret], %[ptr]\n" \
+ asm ("//__per_cpu_" #op "_4\n" \
+ "1: ldxr %w[ret], %[ptr]\n" \
#asm_op " %w[ret], %w[ret], %w[val]\n" \
- "stxr %w[loop], %w[ret], %[ptr]\n" \
- : [loop] "=&r" (loop), [ret] "=&r" (ret), \
- [ptr] "+Q"(*(u32 *)ptr) \
- : [val] "Ir" (val)); \
- } while (loop); \
+ " stxr %w[loop], %w[ret], %[ptr]\n" \
+ " cbnz %w[loop], 1b" \
+ : [loop] "=&r" (loop), [ret] "=&r" (ret), \
+ [ptr] "+Q"(*(u32 *)ptr) \
+ : [val] "Ir" (val)); \
break; \
case 8: \
- do { \
- asm ("//__per_cpu_" #op "_8\n" \
- "ldxr %[ret], %[ptr]\n" \
+ asm ("//__per_cpu_" #op "_8\n" \
+ "1: ldxr %[ret], %[ptr]\n" \
#asm_op " %[ret], %[ret], %[val]\n" \
- "stxr %w[loop], %[ret], %[ptr]\n" \
- : [loop] "=&r" (loop), [ret] "=&r" (ret), \
- [ptr] "+Q"(*(u64 *)ptr) \
- : [val] "Ir" (val)); \
- } while (loop); \
+ " stxr %w[loop], %[ret], %[ptr]\n" \
+ " cbnz %w[loop], 1b" \
+ : [loop] "=&r" (loop), [ret] "=&r" (ret), \
+ [ptr] "+Q"(*(u64 *)ptr) \
+ : [val] "Ir" (val)); \
break; \
default: \
BUILD_BUG(); \
@@ -150,44 +146,40 @@ static inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
switch (size) {
case 1:
- do {
- asm ("//__percpu_xchg_1\n"
- "ldxrb %w[ret], %[ptr]\n"
- "stxrb %w[loop], %w[val], %[ptr]\n"
- : [loop] "=&r"(loop), [ret] "=&r"(ret),
- [ptr] "+Q"(*(u8 *)ptr)
- : [val] "r" (val));
- } while (loop);
+ asm ("//__percpu_xchg_1\n"
+ "1: ldxrb %w[ret], %[ptr]\n"
+ " stxrb %w[loop], %w[val], %[ptr]\n"
+ " cbnz %w[loop], 1b"
+ : [loop] "=&r"(loop), [ret] "=&r"(ret),
+ [ptr] "+Q"(*(u8 *)ptr)
+ : [val] "r" (val));
break;
case 2:
- do {
- asm ("//__percpu_xchg_2\n"
- "ldxrh %w[ret], %[ptr]\n"
- "stxrh %w[loop], %w[val], %[ptr]\n"
- : [loop] "=&r"(loop), [ret] "=&r"(ret),
- [ptr] "+Q"(*(u16 *)ptr)
- : [val] "r" (val));
- } while (loop);
+ asm ("//__percpu_xchg_2\n"
+ "1: ldxrh %w[ret], %[ptr]\n"
+ " stxrh %w[loop], %w[val], %[ptr]\n"
+ " cbnz %w[loop], 1b"
+ : [loop] "=&r"(loop), [ret] "=&r"(ret),
+ [ptr] "+Q"(*(u16 *)ptr)
+ : [val] "r" (val));
break;
case 4:
- do {
- asm ("//__percpu_xchg_4\n"
- "ldxr %w[ret], %[ptr]\n"
- "stxr %w[loop], %w[val], %[ptr]\n"
- : [loop] "=&r"(loop), [ret] "=&r"(ret),
- [ptr] "+Q"(*(u32 *)ptr)
- : [val] "r" (val));
- } while (loop);
+ asm ("//__percpu_xchg_4\n"
+ "1: ldxr %w[ret], %[ptr]\n"
+ " stxr %w[loop], %w[val], %[ptr]\n"
+ " cbnz %w[loop], 1b"
+ : [loop] "=&r"(loop), [ret] "=&r"(ret),
+ [ptr] "+Q"(*(u32 *)ptr)
+ : [val] "r" (val));
break;
case 8:
- do {
- asm ("//__percpu_xchg_8\n"
- "ldxr %[ret], %[ptr]\n"
- "stxr %w[loop], %[val], %[ptr]\n"
- : [loop] "=&r"(loop), [ret] "=&r"(ret),
- [ptr] "+Q"(*(u64 *)ptr)
- : [val] "r" (val));
- } while (loop);
+ asm ("//__percpu_xchg_8\n"
+ "1: ldxr %[ret], %[ptr]\n"
+ " stxr %w[loop], %[val], %[ptr]\n"
+ " cbnz %w[loop], 1b"
+ : [loop] "=&r"(loop), [ret] "=&r"(ret),
+ [ptr] "+Q"(*(u64 *)ptr)
+ : [val] "r" (val));
break;
default:
BUILD_BUG();