Re: [PATCH v3 04/12] KVM: arm64: selftests: Add basic support for arch_timers

[Andrew Jones]

On Wed, Sep 01, 2021 at 09:14:04PM +0000, Raghavendra Rao Ananta wrote:
> Add a minimalistic library support to access the virtual timers,
> that can be used for simple timing functionalities, such as
> introducing delays in the guest.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> ---
>  .../kvm/include/aarch64/arch_timer.h          | 142 ++++++++++++++++++
>  1 file changed, 142 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/include/aarch64/arch_timer.h
> 
> diff --git a/tools/testing/selftests/kvm/include/aarch64/arch_timer.h b/tools/testing/selftests/kvm/include/aarch64/arch_timer.h
> new file mode 100644
> index 000000000000..9df5b63abc47
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/include/aarch64/arch_timer.h
> @@ -0,0 +1,142 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * ARM Generic Timer specific interface
> + */
> +
> +#ifndef SELFTEST_KVM_ARCH_TIMER_H
> +#define SELFTEST_KVM_ARCH_TIMER_H
> +
> +#include "processor.h"
> +
> +enum arch_timer {
> +	VIRTUAL,
> +	PHYSICAL,
> +};
> +
> +#define CTL_ENABLE	(1 << 0)
> +#define CTL_IMASK	(1 << 1)
> +#define CTL_ISTATUS	(1 << 2)
> +
> +#define msec_to_cycles(msec)	\
> +	(timer_get_cntfrq() * (uint64_t)(msec) / 1000)
> +
> +#define usec_to_cycles(usec)	\
> +	(timer_get_cntfrq() * (uint64_t)(usec) / 1000000)
> +
> +#define cycles_to_usec(cycles) \
> +	((uint64_t)(cycles) * 1000000 / timer_get_cntfrq())
> +
> +static inline uint32_t timer_get_cntfrq(void)
> +{
> +	return read_sysreg(cntfrq_el0);
> +}
> +
> +static inline uint64_t timer_get_cntct(enum arch_timer timer)
> +{
> +	isb();
> +
> +	switch (timer) {
> +	case VIRTUAL:
> +		return read_sysreg(cntvct_el0);
> +	case PHYSICAL:
> +		return read_sysreg(cntpct_el0);
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	/* We should not reach here */
> +	return 0;
> +}
> +
> +static inline void timer_set_cval(enum arch_timer timer, uint64_t cval)
> +{
> +	switch (timer) {
> +	case VIRTUAL:
> +		write_sysreg(cntv_cval_el0, cval);
> +		break;
> +	case PHYSICAL:
> +		write_sysreg(cntp_cval_el0, cval);

Huh, looks like we managed to merge a backwards write_sysreg into kvm
selftests. write_sysreg in the kernel and kvm-unit-tests is (value, reg).
We should post a patch fixing that before adding more calls to it.

> +		break;
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	isb();
> +}
> +
> +static inline uint64_t timer_get_cval(enum arch_timer timer)
> +{
> +	switch (timer) {
> +	case VIRTUAL:
> +		return read_sysreg(cntv_cval_el0);
> +	case PHYSICAL:
> +		return read_sysreg(cntp_cval_el0);
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	/* We should not reach here */
> +	return 0;
> +}
> +
> +static inline void timer_set_tval(enum arch_timer timer, uint32_t tval)
> +{
> +	switch (timer) {
> +	case VIRTUAL:
> +		write_sysreg(cntv_tval_el0, tval);
> +		break;
> +	case PHYSICAL:
> +		write_sysreg(cntp_tval_el0, tval);
> +		break;
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	isb();
> +}
> +
> +static inline void timer_set_ctl(enum arch_timer timer, uint32_t ctl)
> +{
> +	switch (timer) {
> +	case VIRTUAL:
> +		write_sysreg(cntv_ctl_el0, ctl);
> +		break;
> +	case PHYSICAL:
> +		write_sysreg(cntp_ctl_el0, ctl);
> +		break;
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	isb();
> +}
> +
> +static inline uint32_t timer_get_ctl(enum arch_timer timer)
> +{
> +	switch (timer) {
> +	case VIRTUAL:
> +		return read_sysreg(cntv_ctl_el0);
> +	case PHYSICAL:
> +		return read_sysreg(cntp_ctl_el0);
> +	default:
> +		GUEST_ASSERT_1(0, timer);
> +	}
> +
> +	/* We should not reach here */
> +	return 0;
> +}

I'll have to look at the test code that uses the above functions, but I
wonder if it wouldn't be better to define two test functions, one for
vtimer and one for ptimer where the sysreg accesses are direct, rather
than all these switched wrappers.

> +
> +static inline void timer_set_next_cval_ms(enum arch_timer timer, uint32_t msec)
> +{
> +	uint64_t now_ct = timer_get_cntct(timer);
> +	uint64_t next_ct = now_ct + msec_to_cycles(msec);
> +
> +	timer_set_cval(timer, next_ct);
> +}
> +
> +static inline void timer_set_next_tval_ms(enum arch_timer timer, uint32_t msec)
> +{
> +	timer_set_tval(timer, msec_to_cycles(msec));
> +}

I'll also look at how these wrappers are used, since open coding them may
be OK.

Thanks,
drew

> +
> +#endif /* SELFTEST_KVM_ARCH_TIMER_H */
> -- 
> 2.33.0.153.gba50c8fa24-goog
> 
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