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

Mark Rutland
2020-07-02T10:29:08Z

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@kernel.org>
> ---
> 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;
| }

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

Mark.