[PATCH v3 18/19] arm64: alternatives: Remove READ_ONCE() usage during patch operation

[Will Deacon]

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 <w...@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;
-- 
2.27.0.383.g050319c2ae-goog

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