From ef5e724b25c9f90b7683bb2d45833ebac0989dcb Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 28 Jul 2015 19:07:28 +0100 Subject: [PATCH] arm64: alternative: put secondary CPUs into polling loop during patch When patching the kernel text with alternatives, we may end up patching parts of the stop_machine state machine (e.g. atomic_dec_and_test in ack_state) and consequently corrupt the instruction stream of any secondary CPUs. This patch passes the cpu_online_mask to stop_machine, forcing all of the CPUs into our own callback which can place the secondary cores into a dumb (but safe!) polling loop whilst the patching is carried out. Signed-off-by: Will Deacon --- arch/arm64/include/asm/alternative.h | 3 ++- arch/arm64/kernel/alternative.c | 29 +++++++++++++++++++++++----- 2 files changed, 26 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index b474e9106bc2..d56ec0715157 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -3,6 +3,7 @@ #ifndef __ASSEMBLY__ +#include #include #include #include @@ -16,7 +17,7 @@ struct alt_instr { u8 alt_len; /* size of new instruction(s), <= orig_len */ }; -void apply_alternatives_all(void); +void __init apply_alternatives_all(void); void apply_alternatives(void *start, size_t length); void free_alternatives_memory(void); diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index 221b98312f0c..fa1d575ab2c2 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -85,7 +85,7 @@ static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr) return insn; } -static int __apply_alternatives(void *alt_region) +static void __apply_alternatives(void *alt_region) { struct alt_instr *alt; struct alt_region *region = alt_region; @@ -114,19 +114,38 @@ static int __apply_alternatives(void *alt_region) flush_icache_range((uintptr_t)origptr, (uintptr_t)(origptr + nr_inst)); } - - return 0; } -void apply_alternatives_all(void) +/* + * We might be patching the stop_machine state machine, so implement a + * really simple polling protocol here. + */ +static int __apply_alternatives_multi_stop(void *unused) { + static int patched = 0; struct alt_region region = { .begin = __alt_instructions, .end = __alt_instructions_end, }; + /* We always have a CPU 0 at this point (__init) */ + if (smp_processor_id()) { + while (!READ_ONCE(patched)) + cpu_relax(); + } else { + BUG_ON(patched); + __apply_alternatives(®ion); + /* Barriers provided by the cache flushing */ + WRITE_ONCE(patched, 1); + } + + return 0; +} + +void __init apply_alternatives_all(void) +{ /* better not try code patching on a live SMP system */ - stop_machine(__apply_alternatives, ®ion, NULL); + stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask); } void apply_alternatives(void *start, size_t length) -- 2.39.5