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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>,
	Suzuki K Pouloze <suzuki.poulose@arm.com>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry@arm.com>
Subject: [PATCH v3 2/2] KVM: arm64: Skip more of the SError vaxorcism
Date: Tue, 18 Jun 2019 16:18:09 +0100	[thread overview]
Message-ID: <20190618151809.259038-3-james.morse@arm.com> (raw)
In-Reply-To: <20190618151809.259038-1-james.morse@arm.com>

During __guest_exit() we need to consume any SError left pending by the
guest so it doesn't contaminate the host. With v8.2 we use the
ESB-instruction. For systems without v8.2, we use dsb+isb and unmask
SError. We do this on every guest exit.

Use the same dsb+isr_el1 trick, this lets us know if an SError is pending
after the dsb, allowing us to skip the isb and self-synchronising PSTATE
write if its not.

This means SError remains masked during KVM's world-switch, so any SError
that occurs during this time is reported by the host, instead of causing
a hyp-panic.

As we're benchmarking this code lets polish the layout. If you give gcc
likely()/unlikely() hints in an if() condition, it shuffles the generated
assembly so that the likely case is immediately after the branch. Lets
do the same here.

Signed-off-by: James Morse <james.morse@arm.com>

Changes since v2:
 * Added isb after the dsb to prevent an early read
---
 arch/arm64/kvm/hyp/entry.S | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 017ec4189a08..269e7b2da1fd 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -162,8 +162,16 @@ alternative_if ARM64_HAS_RAS_EXTN
 	orr	x0, x0, #(1<<ARM_EXIT_WITH_SERROR_BIT)
 1:	ret
 alternative_else
-	// If we have a pending asynchronous abort, now is the
-	// time to find out. From your VAXorcist book, page 666:
+	dsb	sy		// Synchronize against in-flight ld/st
+	isb			// Prevent an early read of side-effect free ISR
+	mrs	x2, isr_el1
+	tbnz	x2, #8, 2f	// ISR_EL1.A
+	ret
+	nop
+2:
+alternative_endif
+	// We know we have a pending asynchronous abort, now is the
+	// time to flush it out. From your VAXorcist book, page 666:
 	// "Threaten me not, oh Evil one!  For I speak with
 	// the power of DEC, and I command thee to show thyself!"
 	mrs	x2, elr_el2
@@ -171,9 +179,7 @@ alternative_else
 	mrs	x4, spsr_el2
 	mov	x5, x0
 
-	dsb	sy		// Synchronize against in-flight ld/st
 	msr	daifclr, #4	// Unmask aborts
-alternative_endif
 
 	// This is our single instruction exception window. A pending
 	// SError is guaranteed to occur at the earliest when we unmask
-- 
2.20.1


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      parent reply	other threads:[~2019-06-18 15:21 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-18 15:18 [PATCH v3 0/2] KVM: arm64: Skip more of the SError vaxorcism James Morse
2019-06-18 15:18 ` [PATCH v3 1/2] KVM: arm64: Re-mask SError after the one instruction window James Morse
2019-06-18 15:18 ` James Morse [this message]

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