[PATCH v1 2/6] KVM: arm64: Consume pending SError as early as possible

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 v1 2/6] KVM: arm64: Consume pending SError as early as possible
Date: Tue,  4 Jun 2019 15:45:47 +0100	[thread overview]
Message-ID: <20190604144551.188107-3-james.morse@arm.com> (raw)
In-Reply-To: <20190604144551.188107-1-james.morse@arm.com>

On systems with v8.2 we switch the 'vaxorcism' of guest SError with an
alternative sequence that uses the ESB-instruction, then reads DISR_EL1.
This saves the unmasking and re-masking of asynchronous exceptions.

We do this after we've saved the guest registers and restored the
host's. Any SError that becomes pending due to this will be accounted
to the guest, when it actually occurred during host-execution.

Move the ESB-instruction as early as possible. Any guest SError
will become pending due to this ESB-instruction and then consumed to
DISR_EL1 before the host touches anything.

This lets us account for host/guest SError precisely on the guest
exit exception boundary.

Signed-off-by: James Morse <james.morse@arm.com>
---
N.B. ESB-instruction is a nop on CPUs that don't support it.

 arch/arm64/include/asm/kvm_asm.h | 2 +-
 arch/arm64/kvm/hyp/entry.S       | 5 ++---
 arch/arm64/kvm/hyp/hyp-entry.S   | 2 ++
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 9170c43b332f..5c9548ae8fa7 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -45,7 +45,7 @@
  * Size of the HYP vectors preamble. kvm_patch_vector_branch() generates code
  * that jumps over this.
  */
-#define KVM_VECTOR_PREAMBLE	4
+#define KVM_VECTOR_PREAMBLE	8
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 93ba3d7ef027..7863ec5266e2 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -138,8 +138,8 @@ ENTRY(__guest_exit)
 
 alternative_if ARM64_HAS_RAS_EXTN
 	// If we have the RAS extensions we can consume a pending error
-	// without an unmask-SError and isb.
-	esb
+	// without an unmask-SError and isb. The ESB-instruction consumed any
+	// pending guest error when we took the exception from the guest.
 	mrs_s	x2, SYS_DISR_EL1
 	str	x2, [x1, #(VCPU_FAULT_DISR - VCPU_CONTEXT)]
 	cbz	x2, 1f
@@ -157,7 +157,6 @@ alternative_else
 	mov	x5, x0
 
 	dsb	sy		// Synchronize against in-flight ld/st
-	nop
 	msr	daifclr, #4	// Unmask aborts
 alternative_endif
 
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 914036e6b6d7..b8d37a987b34 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -230,6 +230,7 @@ ENDPROC(\label)
 .macro valid_vect target
 	.align 7
 661:
+	esb
 	stp	x0, x1, [sp, #-16]!
 662:
 	b	\target
@@ -320,6 +321,7 @@ ENTRY(__bp_harden_hyp_vecs_end)
 	.popsection
 
 ENTRY(__smccc_workaround_1_smc_start)
+	esb
 	sub	sp, sp, #(8 * 4)
 	stp	x2, x3, [sp, #(8 * 0)]
 	stp	x0, x1, [sp, #(8 * 2)]
-- 
2.20.1

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