[3.16.y-ckt stable] Patch "arm: KVM: Disable virtual timer even if the guest is not using it" has been added to staging queue

[Luis Henriques]

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

    arm: KVM: Disable virtual timer even if the guest is not using it

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 3.16.7-ckt19.

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.
-Luis

------

>From 4c41a4b8b3da77d00251cede52f70b597e8e2c34 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier at arm.com>
Date: Wed, 16 Sep 2015 16:18:59 +0100
Subject: arm: KVM: Disable virtual timer even if the guest is not using it

commit 688bc577ac42ae3d07c889a1f0a72f0b23763d58 upstream.

When running a guest with the architected timer disabled (with QEMU and
the kernel_irqchip=off option, for example), it is important to make
sure the timer gets turned off. Otherwise, the guest may try to
enable it anyway, leading to a screaming HW interrupt.

The fix is to unconditionally turn off the virtual timer on guest
exit.

Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm/kvm/interrupts_head.S | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
index 2973b2d342fa..cb1d567ada5e 100644
--- a/arch/arm/kvm/interrupts_head.S
+++ b/arch/arm/kvm/interrupts_head.S
@@ -502,8 +502,7 @@ vcpu	.req	r0		@ vcpu pointer always in r0

 	mrc	p15, 0, r2, c14, c3, 1	@ CNTV_CTL
 	str	r2, [vcpu, #VCPU_TIMER_CNTV_CTL]
-	bic	r2, #1			@ Clear ENABLE
-	mcr	p15, 0, r2, c14, c3, 1	@ CNTV_CTL
+
 	isb

 	mrrc	p15, 3, r2, r3, c14	@ CNTV_CVAL
@@ -516,6 +515,9 @@ vcpu	.req	r0		@ vcpu pointer always in r0
 	mcrr	p15, 4, r2, r2, c14	@ CNTVOFF

 1:
+	mov	r2, #0			@ Clear ENABLE
+	mcr	p15, 0, r2, c14, c3, 1	@ CNTV_CTL
+
 #endif
 	@ Allow physical timer/counter access for the host
 	mrc	p15, 4, r2, c14, c1, 0	@ CNTHCTL