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From: James Morse <james.morse@arm.com>
To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Cc: Suzuki K Pouloze <suzuki.poulose@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Julien Thierry <julien.thierry@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	James Morse <james.morse@arm.com>
Subject: [PATCH v1 5/6] KVM: arm64: nop out dsb in __guest_enter() unless we have v8.2 RAS
Date: Tue,  4 Jun 2019 15:45:50 +0100	[thread overview]
Message-ID: <20190604144551.188107-6-james.morse@arm.com> (raw)
In-Reply-To: <20190604144551.188107-1-james.morse@arm.com>

Previously we added a dsb before reading isr_el1 to ensure that the
hosts write's have finished, before we read isr_el1 to see if any of
them caused an SError.

This only really matters if we have the v8.2 RAS extensions with its
poison tracking and containment reporting via SError's ESR value.
Before v8.2 it is very unlikely these systems will detect and report
errors in a way that we can handle.

Use alternatives to remove this barrier on systems without v8.2 RAS.

Signed-off-by: James Morse <james.morse@arm.com>
---
Tested on A57 with v5.2-rc1, do_hvc from [0]
v5.2-rc1            mean:4339 stddev:33
v5.2-rc1+patches1-5 mean:4405 stddev:31
with series 1.53% slower
[0]https://git.kernel.org/pub/scm/linux/kernel/git/maz/kvm-ws-tests.git/

 arch/arm64/kvm/hyp/entry.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index fa39899fe3d0..a5a4254314a1 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -17,6 +17,7 @@
 
 #include <linux/linkage.h>
 
+#include <asm/alternative.h>
 #include <asm/asm-offsets.h>
 #include <asm/assembler.h>
 #include <asm/fpsimdmacros.h>
@@ -65,8 +66,11 @@ ENTRY(__guest_enter)
 
 	// Now the host state is stored if we have a pending RAS SError it must
 	// affect the host. If any asyncronous exception is pending we defer
-	// the guest entry.
+	// the guest entry. The DSB isn't necessary before v8.2 as any SError
+	// would be fatal.
+alternative_if ARM64_HAS_RAS_EXTN
 	dsb	nshst
+alternative_else_nop_endif
 	mrs	x1, isr_el1
 	cbz	x1,  1f
 	mov	x0, #ARM_EXCEPTION_IRQ
-- 
2.20.1


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  parent reply	other threads:[~2019-06-04 14:54 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-04 14:45 [PATCH v1 0/6] KVM: arm64: Account host/guest SError more precisely (Neoverse-N1 #1349291) James Morse
2019-06-04 14:45 ` [PATCH v1 1/6] KVM: arm64: Abstract the size of the HYP vectors pre-amble James Morse
2019-06-05  8:58   ` Julien Thierry
2019-06-04 14:45 ` [PATCH v1 2/6] KVM: arm64: Consume pending SError as early as possible James Morse
2019-06-05  9:00   ` Julien Thierry
2019-06-05 11:03     ` James Morse
2019-06-04 14:45 ` [PATCH v1 3/6] KVM: arm64: Defer guest entry when an asynchronous exception is pending James Morse
2019-06-04 14:45 ` [PATCH v1 4/6] arm64: Update silicon-errata.txt for Neoverse-N1 #1349291 James Morse
2019-06-04 14:45 ` James Morse [this message]
2019-06-04 14:45 ` [PATCH v1 6/6] KVM: arm64: Skip more of the SError vaxorcism James Morse

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