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Subject[PATCH 17/18] arm64: alternatives: Remove READ_ONCE() usage during patch operation
Date
In preparation for patching the internals of READ_ONCE() itself, replace
its usage on the alternatives patching patch with a volatile variable
instead.

Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kernel/alternative.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index d1757ef1b1e7..87bca8d44084 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -21,7 +21,8 @@
#define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset)
#define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset)

-static int all_alternatives_applied;
+/* Volatile, as we may be patching the guts of READ_ONCE() */
+static volatile int all_alternatives_applied;

static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);

@@ -217,7 +218,7 @@ static int __apply_alternatives_multi_stop(void *unused)

/* We always have a CPU 0 at this point (__init) */
if (smp_processor_id()) {
- while (!READ_ONCE(all_alternatives_applied))
+ while (!all_alternatives_applied)
cpu_relax();
isb();
} else {
@@ -229,7 +230,7 @@ static int __apply_alternatives_multi_stop(void *unused)
BUG_ON(all_alternatives_applied);
__apply_alternatives(&region, false, remaining_capabilities);
/* Barriers provided by the cache flushing */
- WRITE_ONCE(all_alternatives_applied, 1);
+ all_alternatives_applied = 1;
}

return 0;
--
2.27.0.212.ge8ba1cc988-goog
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