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arm64: alternative: put secondary CPUs into polling loop during patch

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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 <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2015-07-28 19:07:28 +01:00
parent 6c020ea8dc
commit ef5e724b25
2 changed files with 26 additions and 6 deletions
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3
arch/arm64/include/asm/alternative.h
View File

@ -3,6 +3,7 @@
#ifndef __ASSEMBLY__
#include <linux/init.h>
#include <linux/kconfig.h>
#include <linux/types.h>
#include <linux/stddef.h>
@ -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);

29
arch/arm64/kernel/alternative.c
View File

@ -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(&region);
/* 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, &region, NULL);
stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
}
void apply_alternatives(void *start, size_t length)