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| 2 |
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| 3 | |
| 4 | * Definitions for the clocksource provided by the Hyper-V
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| 5 | * hypervisor to guest VMs, as described in the Hyper-V Top
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| 6 | * Level Functional Spec (TLFS).
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| 7 | *
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| 8 | * Copyright (C) 2019, Microsoft, Inc.
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| 9 | *
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| 10 | * Author: Michael Kelley <[email protected]>
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| 11 |
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| 12 |
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| 13 | #ifndef __CLKSOURCE_HYPERV_TIMER_H
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| 14 | #define __CLKSOURCE_HYPERV_TIMER_H
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| 15 |
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| 16 | #include <linux/clocksource.h>
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| 17 | #include <linux/math64.h>
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| 18 | #include <asm/mshyperv.h>
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| 19 |
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| 20 | #define HV_MAX_MAX_DELTA_TICKS 0xffffffff
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| 21 | #define HV_MIN_DELTA_TICKS 1
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| 22 |
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| 23 |
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| 24 | extern int hv_stimer_alloc(bool have_percpu_irqs);
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| 25 | extern int hv_stimer_cleanup(unsigned int cpu);
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| 26 | extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
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| 27 | extern void hv_stimer_legacy_cleanup(unsigned int cpu);
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| 28 | extern void hv_stimer_global_cleanup(void);
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| 29 | extern void hv_stimer0_isr(void);
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| 30 |
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| 31 | #ifdef CONFIG_HYPERV_TIMER
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| 32 | extern u64 (*hv_read_reference_counter)(void);
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| 33 | extern void hv_init_clocksource(void);
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| 34 |
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| 35 | extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
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| 36 |
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| 37 | static inline notrace u64
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| 38 | hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
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| 39 | {
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| 40 | u64 scale, offset;
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| 41 | u32 sequence;
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| 42 |
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| 43 | |
| 44 | * The protocol for reading Hyper-V TSC page is specified in Hypervisor
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| 45 | * Top-Level Functional Specification ver. 3.0 and above. To get the
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| 46 | * reference time we must do the following:
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| 47 | * - READ ReferenceTscSequence
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| 48 | * A special '0' value indicates the time source is unreliable and we
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| 49 | * need to use something else. The currently published specification
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| 50 | * versions (up to 4.0b) contain a mistake and wrongly claim '-1'
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| 51 | * instead of '0' as the special value, see commit c35b82ef0294.
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| 52 | * - ReferenceTime =
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| 53 | * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
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| 54 | * - READ ReferenceTscSequence again. In case its value has changed
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| 55 | * since our first reading we need to discard ReferenceTime and repeat
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| 56 | * the whole sequence as the hypervisor was updating the page in
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| 57 | * between.
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| 58 |
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| 59 | do {
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| 60 | sequence = READ_ONCE(tsc_pg->tsc_sequence);
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| 61 | if (!sequence)
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| 62 | return U64_MAX;
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| 63 | |
| 64 | * Make sure we read sequence before we read other values from
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| 65 | * TSC page.
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| 66 |
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| 67 | smp_rmb();
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| 68 |
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| 69 | scale = READ_ONCE(tsc_pg->tsc_scale);
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| 70 | offset = READ_ONCE(tsc_pg->tsc_offset);
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| 71 | *cur_tsc = hv_get_raw_timer();
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| 72 |
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| 73 | |
| 74 | * Make sure we read sequence after we read all other values
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| 75 | * from TSC page.
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| 76 |
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| 77 | smp_rmb();
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| 78 |
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| 79 | } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
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| 80 |
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| 81 | return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
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| 82 | }
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| 83 |
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| 84 | static inline notrace u64
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| 85 | hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
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| 86 | {
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| 87 | u64 cur_tsc;
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| 88 |
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| 89 | return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
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| 90 | }
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| 91 |
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| 92 | #else
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| 93 | static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
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| 94 | {
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| 95 | return NULL;
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| 96 | }
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| 97 |
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| 98 | static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
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| 99 | u64 *cur_tsc)
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| 100 | {
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| 101 | return U64_MAX;
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| 102 | }
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| 103 | #endif
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| 104 |
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| 105 | #endif
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