Commit 9397fa2e authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

clocksource: hyper-v: Adjust hv_read_tsc_page_tsc() to avoid special casing U64_MAX 



Currently hv_read_tsc_page_tsc() (ab)uses the (valid) time value of
U64_MAX as an error return. This breaks the clean wrap-around of the
clock.

Modify the function signature to return a boolean state and provide
another u64 pointer to store the actual time on success. This obviates
the need to steal one time value and restores the full counter width.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Tested-by: Michael Kelley <mikelley@microsoft.com>  # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.775630881@infradead.org
parent 77750f78

arch/x86/include/asm/vdso/gettimeofday.h

+6 −4
Original line number Diff line number Diff line
@@ -238,10 +238,12 @@ static u64 vread_pvclock(void) 
#ifdef CONFIG_HYPERV_TIMER

static u64 vread_hvclock(void)

{

	u64 ret = hv_read_tsc_page(&hvclock_page);

	if (likely(ret != U64_MAX))

		ret &= S64_MAX;

	return ret;

	u64 tsc, time;



	if (hv_read_tsc_page_tsc(&hvclock_page, &tsc, &time))

		return time & S64_MAX;



	return U64_MAX;

}

#endif

arch/x86/kvm/x86.c

+3 −4
Original line number Diff line number Diff line
@@ -2799,14 +2799,13 @@ static u64 read_tsc(void) 
static inline u64 vgettsc(struct pvclock_clock *clock, u64 *tsc_timestamp,

			  int *mode)

{

	long v;

	u64 tsc_pg_val;

	long v;



	switch (clock->vclock_mode) {

	case VDSO_CLOCKMODE_HVCLOCK:

		tsc_pg_val = hv_read_tsc_page_tsc(hv_get_tsc_page(),

						  tsc_timestamp);

		if (tsc_pg_val != U64_MAX) {

		if (hv_read_tsc_page_tsc(hv_get_tsc_page(),

					 tsc_timestamp, &tsc_pg_val)) {

			/* TSC page valid */

			*mode = VDSO_CLOCKMODE_HVCLOCK;

			v = (tsc_pg_val - clock->cycle_last) &

drivers/clocksource/hyperv_timer.c

+11 −5
Original line number Diff line number Diff line
@@ -393,14 +393,20 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) 
}

EXPORT_SYMBOL_GPL(hv_get_tsc_page);



static u64 notrace read_hv_clock_tsc(void)

static notrace u64 read_hv_clock_tsc(void)

{

	u64 current_tick = hv_read_tsc_page(hv_get_tsc_page());

	u64 cur_tsc, time;



	if (current_tick == U64_MAX)

		current_tick = hv_get_register(HV_REGISTER_TIME_REF_COUNT);

	/*

	 * The Hyper-V Top-Level Function Spec (TLFS), section Timers,

	 * subsection Refererence Counter, guarantees that the TSC and MSR

	 * times are in sync and monotonic. Therefore we can fall back

	 * to the MSR in case the TSC page indicates unavailability.

	 */

	if (!hv_read_tsc_page_tsc(tsc_page, &cur_tsc, &time))

		time = hv_get_register(HV_REGISTER_TIME_REF_COUNT);



	return current_tick;

	return time;

}



static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)

include/clocksource/hyperv_timer.h

+9 −15
Original line number Diff line number Diff line
@@ -38,8 +38,9 @@ extern void hv_remap_tsc_clocksource(void); 
extern unsigned long hv_get_tsc_pfn(void);

extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);



static inline notrace u64

hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)

static __always_inline bool

hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,

		     u64 *cur_tsc, u64 *time)

{

	u64 scale, offset;

	u32 sequence;
@@ -63,7 +64,7 @@ hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc) 
	do {

		sequence = READ_ONCE(tsc_pg->tsc_sequence);

		if (!sequence)

			return U64_MAX;

			return false;

		/*

		 * Make sure we read sequence before we read other values from

		 * TSC page.
@@ -82,15 +83,8 @@ hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc) 


	} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);



	return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;

}



static inline notrace u64

hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)

{

	u64 cur_tsc;



	return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);

	*time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;

	return true;

}



#else /* CONFIG_HYPERV_TIMER */
@@ -104,10 +98,10 @@ static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void) 
	return NULL;

}



static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,

				       u64 *cur_tsc)

static __always_inline bool

hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)

{

	return U64_MAX;

	return false;

}



static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }