linux-kernel - [PATCH 3.16.y-ckt 122/135] clocksource: arch_timer: Only use the virtual counter (CNTVCT) on arm64

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Date:	Fri,  6 Feb 2015 12:01:40 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Mark Rutland <mark.rutland@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 122/135] clocksource: arch_timer: Only use the virtual counter (CNTVCT) on arm64

3.16.7-ckt6 -stable review patch.  If anyone has any objections, please let me know.

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

From: Catalin Marinas <catalin.marinas@....com>

commit d6ad36913083d683aad4e02e53580c995f1a6ede upstream.

Commit 0b46b8a718c6 (clocksource: arch_timer: Fix code to use physical
timers when requested) introduces the use of physical counters in the
ARM architected timer driver. However, he arm64 kernel uses CNTVCT in
VDSO. When booting in EL2, the kernel switches to the physical timers to
make things easier for KVM but it continues to use the virtual counter
both in user and kernel. While in such scenario CNTVCT == CNTPCT (since
CNTVOFF is initialised by the kernel to 0), we want to spot firmware
bugs corrupting CNTVOFF early (which would affect CNTVCT).

Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Tested-by: Yingjoe Chen <yingjoe.chen@...iatek.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/clocksource/arm_arch_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 506949d2e922..499cb1de5e99 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -430,7 +430,7 @@ static void __init arch_counter_register(unsigned type)
 
 	/* Register the CP15 based counter if we have one */
 	if (type & ARCH_CP15_TIMER) {
-		if (arch_timer_use_virtual)
+		if (IS_ENABLED(CONFIG_ARM64) || arch_timer_use_virtual)
 			arch_timer_read_counter = arch_counter_get_cntvct;
 		else
 			arch_timer_read_counter = arch_counter_get_cntpct;
-- 
2.1.4

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