Re: [PATCH 2/3] arm64: arch_timer: Allow an workaround descriptor to provide vdso_clock_mode

[Marc Zyngier]

On 2020-07-02 11:28, Mark Rutland wrote:
> On Wed, Jul 01, 2020 at 05:18:23PM +0100, Marc Zyngier wrote:
> > As we are about to disable the vdso for compat tasks in some 
> > circumstances,
> > let's allow a workaround descriptor to provide the vdso_clock_mode 
> > that
> > matches the platform.
> >
> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> > ---
> >  arch/arm64/include/asm/arch_timer.h  | 3 +++
> >  drivers/clocksource/arm_arch_timer.c | 3 +++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/arch_timer.h 
> > b/arch/arm64/include/asm/arch_timer.h
> > index 7ae54d7d333a..fb8dfcbf9c01 100644
> > --- a/arch/arm64/include/asm/arch_timer.h
> > +++ b/arch/arm64/include/asm/arch_timer.h
> > @@ -18,6 +18,8 @@
> >  #include <linux/smp.h>
> >  #include <linux/types.h>
> >
> > +#include <vdso/clocksource.h>
> > +
> >  #include <clocksource/arm_arch_timer.h>
> >
> >  #if IS_ENABLED(CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND)
> > @@ -58,6 +60,7 @@ struct arch_timer_erratum_workaround {
> >  	u64 (*read_cntvct_el0)(void);
> >  	int (*set_next_event_phys)(unsigned long, struct clock_event_device 
> > *);
> >  	int (*set_next_event_virt)(unsigned long, struct clock_event_device 
> > *);
> > +	enum vdso_clock_mode vdso_clock_mode;
> >  };
> >
> >  DECLARE_PER_CPU(const struct arch_timer_erratum_workaround *,
> > diff --git a/drivers/clocksource/arm_arch_timer.c 
> > b/drivers/clocksource/arm_arch_timer.c
> > index ecf7b7db2d05..f828835c568f 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -566,6 +566,9 @@ void arch_timer_enable_workaround(const struct 
> > arch_timer_erratum_workaround *wa
> >  	if (wa->read_cntvct_el0) {
> >  		clocksource_counter.vdso_clock_mode = VDSO_CLOCKMODE_NONE;
> >  		vdso_default = VDSO_CLOCKMODE_NONE;
> > +	} else {
> > +		clocksource_counter.vdso_clock_mode = wa->vdso_clock_mode;
> > +		vdso_default = wa->vdso_clock_mode;
> >  	}
>
> I fear that we're liable to forget to set vdso_clock_mode on new errata
> that don't need a read_cntvct_el0 hook, and if so we'll happen to set
> these to 0 (i.e. VDSO_CLOCKMODE_NONE).
>
> For now could we instead have a boolan disable_compat_vdso, with this
> being:
>
> | if (wa->read_cntvct_el0) {
> | 	clocksource_counter.vdso_clock_mode = VDSO_CLOCKMODE_NONE;
> | 	vdso_default = VDSO_CLOCKMODE_NONE;
> | } else if (wa->disable_compat_vdso) {
> | 	clocksource_counter.vdso_clock_mode = 
> VDSO_CLOCKMODE_ARCHTIMER_NOCOMPAT;
> | 	vdso_default = wa->vdso_clock_mode = 
> VDSO_CLOCKMODE_ARCHTIMER_NOCOMPAT;
> | }

Sure, that'd work too.

> Do we need to handle the comination of a workaround seeting NONE and 
> one
> setting ARCHTIMER_NOCOMPAT?

Not yet. Probably coming any time now. Which is why we may need to
look into per-CPU vdso data pages (Broonie has a series that could
be of some use, apparently).

Thanks,

        M.
--
Jazz is not dead. It just smells funny...