Subject: [PATCH] clocksource: arch_timer: Only use the virtual counter (CNTVCT) on arm64

From: [email-masked] (Mark Rutland)
Date: Mon, 15 Dec 2014 10:58:35 +0000

Hi Daniel,

On Wed, Dec 10, 2014 at 11:04:38AM +0000, Daniel Lezcano wrote:
> On 12/10/2014 12:02 PM, Catalin Marinas wrote:
> > 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 <[email-masked]>
> > Tested-by: Yingjoe Chen <[email-masked]>
> > Cc: Daniel Lezcano <[email-masked]>
> > ---
> >
> > Daniel,
> >
> > Do you plan to take this patch and push into mainline (ideally before -rc1)?
> > Otherwise we can push it via the arm64 tree.
> 
> I will take care of it.
> 
> Thanks !
> 
>    -- Daniel

What's the state of this patch?

It doesn't seem to be in linux-next (next-20141215), which is failing to
boot for me due to hitting the BUG in the arm64 arch_counter_get_cntpct.

Thanks,
Mark.

> 
> >
> > Thanks,
> >
> > Catalin
> >
> >
> >   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 6a79fc4f900c..095c1774592c 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -462,7 +462,7 @@ 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;
> >
> 
> 
> -- 
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