The ESB-instruction is a nop on CPUs that don't implement the RAS
extensions. This lets us use it in places like the vectors without
having to use alternatives.
If someone disables CONFIG_ARM64_RAS_EXTN, this instruction still has
its RAS extensions behaviour, but we no longer read DISR_EL1 as this
register does depend on alternatives.
This could go wrong if we want to synchronize an SError from a KVM
guest. On a CPU that has the RAS extensions, but the KConfig option
was disabled, we consume the pending SError with no chance of ever
reading it.
Hide the ESB-instruction behind the CONFIG_ARM64_RAS_EXTN option,
outputting a regular nop if the feature has been disabled.
Reported-by: Julien Thierry <julien.thie...@arm.com>
Signed-off-by: James Morse <james.mo...@arm.com>
---
New for v2. The esb where this would be a problem is added later in
this series, but there is no build-dependency.
---
arch/arm64/include/asm/assembler.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/arm64/include/asm/assembler.h
b/arch/arm64/include/asm/assembler.h
index 92b6b7cf67dd..2d2114b39846 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -107,7 +107,11 @@
* RAS Error Synchronization barrier
*/
.macro esb
+#ifdef CONFIG_ARM64_RAS_EXTN
hint #16
+#else
+ nop
+#endif
.endm
/*
--
2.20.1
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