From: James Morse james.morse@arm.com
[ Upstream commit 2b68a2a963a157f024c67c0697b16f5f792c8a35 ]
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.thierry@arm.com Signed-off-by: James Morse james.morse@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 570d195a184d..e3a15c751b13 100644 --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -96,7 +96,11 @@ * RAS Error Synchronization barrier */ .macro esb +#ifdef CONFIG_ARM64_RAS_EXTN hint #16 +#else + nop +#endif .endm
/*