[3.16.y-ckt stable] Patch "KVM: arm64: add workaround for Cortex-A57 erratum #852523" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    KVM: arm64: add workaround for Cortex-A57 erratum #852523

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.19.8-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 88645476818b8aab2403d70cee40f8dd259044c7 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon at arm.com>
Date: Mon, 14 Sep 2015 16:06:03 +0100
Subject: KVM: arm64: add workaround for Cortex-A57 erratum #852523

commit 43297dda0a51e4ffed0888ce727c218cfb7474b6 upstream.

When restoring the system register state for an AArch32 guest at EL2,
writes to DACR32_EL2 may not be correctly synchronised by Cortex-A57,
which can lead to the guest effectively running with junk in the DACR
and running into unexpected domain faults.

This patch works around the issue by re-ordering our restoration of the
AArch32 register aliases so that they happen before the AArch64 system
registers. Ensuring that the registers are restored in this order
guarantees that they will be correctly synchronised by the core.

Reviewed-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/kvm/hyp.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index c3ca89c..cbaa8bc 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -946,13 +946,15 @@ ENTRY(__kvm_vcpu_run)
 	// Guest context
 	add	x2, x0, #VCPU_CONTEXT

+	// We must restore the 32-bit state before the sysregs, thanks
+	// to Cortex-A57 erratum #852523.
+	restore_guest_32bit_state
 	bl __restore_sysregs
 	bl __restore_fpsimd

 	skip_debug_state x3, 1f
 	bl	__restore_debug
 1:
-	restore_guest_32bit_state
 	restore_guest_regs

 	// That's it, no more messing around.
--
1.9.1