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arm64: assembler: Switch ESB-instruction with a vanilla nop if !ARM64_HAS_RAS

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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>
This commit is contained in:
James Morse 2019-06-18 16:17:33 +01:00 committed by Marc Zyngier
parent 4b972a01a7
commit 2b68a2a963
1 changed files with 4 additions and 0 deletions
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4
arch/arm64/include/asm/assembler.h
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@ -96,7 +96,11 @@
* RAS Error Synchronization barrier
*/
.macro esb
#ifdef CONFIG_ARM64_RAS_EXTN
hint #16
#else
nop
#endif
.endm
/*