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

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Michael Kelley <mikelley@microsoft.com>  # Hyper-V
Link: https://lore.kernel.org/r/20230519102715.775630881@infradead.org
This commit is contained in:
Peter Zijlstra 2023-05-19 12:21:07 +02:00
parent 77750f78b0
commit 9397fa2ea3
4 changed files with 29 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

10
arch/x86/include/asm/vdso/gettimeofday.h
View file

@ -238,10 +238,12 @@ static u64 vread_pvclock(void)
#ifdef CONFIG_HYPERV_TIMER #ifdef CONFIG_HYPERV_TIMER
static u64 vread_hvclock(void) static u64 vread_hvclock(void)
{ {
u64 ret = hv_read_tsc_page(&hvclock_page); u64 tsc, time;
if (likely(ret != U64_MAX))
ret &= S64_MAX; if (hv_read_tsc_page_tsc(&hvclock_page, &tsc, &time))
return ret; return time & S64_MAX;
return U64_MAX;
} }
#endif #endif

7
arch/x86/kvm/x86.c
View file

@ -2799,14 +2799,13 @@ static u64 read_tsc(void)
static inline u64 vgettsc(struct pvclock_clock *clock, u64 *tsc_timestamp, static inline u64 vgettsc(struct pvclock_clock *clock, u64 *tsc_timestamp,
int *mode) int *mode)
{ {
long v;
u64 tsc_pg_val; u64 tsc_pg_val;
long v;
switch (clock->vclock_mode) { switch (clock->vclock_mode) {
case VDSO_CLOCKMODE_HVCLOCK: case VDSO_CLOCKMODE_HVCLOCK:
tsc_pg_val = hv_read_tsc_page_tsc(hv_get_tsc_page(), if (hv_read_tsc_page_tsc(hv_get_tsc_page(),
tsc_timestamp); tsc_timestamp, &tsc_pg_val)) {
if (tsc_pg_val != U64_MAX) {
/* TSC page valid */ /* TSC page valid */
*mode = VDSO_CLOCKMODE_HVCLOCK; *mode = VDSO_CLOCKMODE_HVCLOCK;
v = (tsc_pg_val - clock->cycle_last) & v = (tsc_pg_val - clock->cycle_last) &

16
drivers/clocksource/hyperv_timer.c
View file

@ -393,14 +393,20 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
} }
EXPORT_SYMBOL_GPL(hv_get_tsc_page); 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) static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)

24
include/clocksource/hyperv_timer.h
View file

@ -38,8 +38,9 @@ extern void hv_remap_tsc_clocksource(void);
extern unsigned long hv_get_tsc_pfn(void); extern unsigned long hv_get_tsc_pfn(void);
extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void); extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
static inline notrace u64 static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc) hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
u64 *cur_tsc, u64 *time)
{ {
u64 scale, offset; u64 scale, offset;
u32 sequence; u32 sequence;
@ -63,7 +64,7 @@ hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
do { do {
sequence = READ_ONCE(tsc_pg->tsc_sequence); sequence = READ_ONCE(tsc_pg->tsc_sequence);
if (!sequence) if (!sequence)
return U64_MAX; return false;
/* /*
* Make sure we read sequence before we read other values from * Make sure we read sequence before we read other values from
* TSC page. * 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); } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset; *time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
} return true;
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);
} }
#else /* CONFIG_HYPERV_TIMER */ #else /* CONFIG_HYPERV_TIMER */
@ -104,10 +98,10 @@ static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
return NULL; return NULL;
} }
static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, static __always_inline bool
u64 *cur_tsc) 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; } static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }