1 /* SPDX-License-Identifier: GPL-2.0 */ 2 3 /* 4 * Definitions for the clocksource provided by the Hyper-V 5 * hypervisor to guest VMs, as described in the Hyper-V Top 6 * Level Functional Spec (TLFS). 7 * 8 * Copyright (C) 2019, Microsoft, Inc. 9 * 10 * Author: Michael Kelley <mikelley@microsoft.com> 11 */ 12 13 #ifndef __CLKSOURCE_HYPERV_TIMER_H 14 #define __CLKSOURCE_HYPERV_TIMER_H 15 16 #include <linux/clocksource.h> 17 #include <linux/math64.h> 18 #include <asm/mshyperv.h> 19 20 #define HV_MAX_MAX_DELTA_TICKS 0xffffffff 21 #define HV_MIN_DELTA_TICKS 1 22 23 /* Routines called by the VMbus driver */ 24 extern int hv_stimer_alloc(int sint); 25 extern void hv_stimer_free(void); 26 extern void hv_stimer_init(unsigned int cpu); 27 extern void hv_stimer_cleanup(unsigned int cpu); 28 extern void hv_stimer_global_cleanup(void); 29 extern void hv_stimer0_isr(void); 30 31 #if IS_ENABLED(CONFIG_HYPERV) 32 extern struct clocksource *hyperv_cs; 33 extern void hv_init_clocksource(void); 34 #endif /* CONFIG_HYPERV */ 35 36 #ifdef CONFIG_HYPERV_TSCPAGE 37 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void); 38 39 static inline notrace u64 40 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc) 41 { 42 u64 scale, offset; 43 u32 sequence; 44 45 /* 46 * The protocol for reading Hyper-V TSC page is specified in Hypervisor 47 * Top-Level Functional Specification ver. 3.0 and above. To get the 48 * reference time we must do the following: 49 * - READ ReferenceTscSequence 50 * A special '0' value indicates the time source is unreliable and we 51 * need to use something else. The currently published specification 52 * versions (up to 4.0b) contain a mistake and wrongly claim '-1' 53 * instead of '0' as the special value, see commit c35b82ef0294. 54 * - ReferenceTime = 55 * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset 56 * - READ ReferenceTscSequence again. In case its value has changed 57 * since our first reading we need to discard ReferenceTime and repeat 58 * the whole sequence as the hypervisor was updating the page in 59 * between. 60 */ 61 do { 62 sequence = READ_ONCE(tsc_pg->tsc_sequence); 63 if (!sequence) 64 return U64_MAX; 65 /* 66 * Make sure we read sequence before we read other values from 67 * TSC page. 68 */ 69 smp_rmb(); 70 71 scale = READ_ONCE(tsc_pg->tsc_scale); 72 offset = READ_ONCE(tsc_pg->tsc_offset); 73 *cur_tsc = hv_get_raw_timer(); 74 75 /* 76 * Make sure we read sequence after we read all other values 77 * from TSC page. 78 */ 79 smp_rmb(); 80 81 } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence); 82 83 return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset; 84 } 85 86 static inline notrace u64 87 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg) 88 { 89 u64 cur_tsc; 90 91 return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc); 92 } 93 94 #else /* CONFIG_HYPERV_TSC_PAGE */ 95 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void) 96 { 97 return NULL; 98 } 99 100 static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, 101 u64 *cur_tsc) 102 { 103 return U64_MAX; 104 } 105 #endif /* CONFIG_HYPERV_TSCPAGE */ 106 107 #endif 108