linux-kernel - [PATCH 4.2 037/134] arm64: KVM: Disable virtual timer even if the guest is not using it

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Date:	Sat, 26 Sep 2015 13:54:49 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>
Subject: [PATCH 4.2 037/134] arm64: KVM: Disable virtual timer even if the guest is not using it

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Zyngier <marc.zyngier@....com>

commit c4cbba9fa078f55d9f6d081dbb4aec7cf969e7c7 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.

Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm64/kvm/hyp.S |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -840,8 +840,6 @@
 	mrs	x3, cntv_ctl_el0
 	and	x3, x3, #3
 	str	w3, [x0, #VCPU_TIMER_CNTV_CTL]
-	bic	x3, x3, #1		// Clear Enable
-	msr	cntv_ctl_el0, x3
 
 	isb
 
@@ -849,6 +847,9 @@
 	str	x3, [x0, #VCPU_TIMER_CNTV_CVAL]
 
 1:
+	// Disable the virtual timer
+	msr	cntv_ctl_el0, xzr
+
 	// Allow physical timer/counter access for the host
 	mrs	x2, cnthctl_el2
 	orr	x2, x2, #3


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