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From: James Morse <james.morse@arm.com>
To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Cc: Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>
Subject: [PATCH v2 1/6] arm64: assember: Switch ESB-instruction with a vanilla nop if !ARM64_HAS_RAS
Date: Mon, 10 Jun 2019 17:24:22 +0100
Message-ID: <20190610162427.115910-2-james.morse@arm.com> (raw)
In-Reply-To: <20190610162427.115910-1-james.morse@arm.com>

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 --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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Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 16:24 [PATCH v2 0/6] KVM: arm64: Account host/guest SError more precisely (Neoverse-N1 #1349291) James Morse
2019-06-10 16:24 ` James Morse [this message]
2019-06-10 16:24 ` [PATCH v2 2/6] KVM: arm64: Abstract the size of the HYP vectors pre-amble James Morse
2019-06-10 16:24 ` [PATCH v2 3/6] KVM: arm64: Make indirect vectors preamble behaviour symmetric James Morse
2019-06-10 16:24 ` [PATCH v2 4/6] KVM: arm64: Consume pending SError as early as possible James Morse
2019-06-10 16:24 ` [PATCH v2 5/6] KVM: arm64: Defer guest entry when an asynchronous exception is pending James Morse
2019-06-10 17:01   ` Marc Zyngier
2019-06-10 16:24 ` [PATCH v2 6/6] arm64: Update silicon-errata.txt for Neoverse-N1 #1349291 James Morse

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