diff mbox series

[v2,1/6] arm64: assember: Switch ESB-instruction with a vanilla nop if !ARM64_HAS_RAS

Message ID 20190610162427.115910-2-james.morse@arm.com (mailing list archive)
State New, archived
Headers show
Series KVM: arm64: Account host/guest SError more precisely (Neoverse-N1 #1349291) | expand

Commit Message

James Morse June 10, 2019, 4:24 p.m. UTC 
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>
---
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 mbox series

Patch

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
 
 /*