include/clocksource/hyperv_timer.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002
0003 /*
0004  * Definitions for the clocksource provided by the Hyper-V
0005  * hypervisor to guest VMs, as described in the Hyper-V Top
0006  * Level Functional Spec (TLFS).
0007  *
0008  * Copyright (C) 2019, Microsoft, Inc.
0009  *
0010  * Author:  Michael Kelley <mikelley@microsoft.com>
0011  */
0012
0013 #ifndef __CLKSOURCE_HYPERV_TIMER_H
0014 #define __CLKSOURCE_HYPERV_TIMER_H
0015
0016 #include <linux/clocksource.h>
0017 #include <linux/math64.h>
0018 #include <asm/mshyperv.h>
0019
0020 #define HV_MAX_MAX_DELTA_TICKS 0xffffffff
0021 #define HV_MIN_DELTA_TICKS 1
0022
0023 #ifdef CONFIG_HYPERV_TIMER
0024
0025 /* Routines called by the VMbus driver */
0026 extern int hv_stimer_alloc(bool have_percpu_irqs);
0027 extern int hv_stimer_cleanup(unsigned int cpu);
0028 extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
0029 extern void hv_stimer_legacy_cleanup(unsigned int cpu);
0030 extern void hv_stimer_global_cleanup(void);
0031 extern void hv_stimer0_isr(void);
0032
0033 extern void hv_init_clocksource(void);
0034
0035 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
0036
0037 static inline notrace u64
0038 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
0039 {
0040     u64 scale, offset;
0041     u32 sequence;
0042
0043     /*
0044      * The protocol for reading Hyper-V TSC page is specified in Hypervisor
0045      * Top-Level Functional Specification ver. 3.0 and above. To get the
0046      * reference time we must do the following:
0047      * - READ ReferenceTscSequence
0048      *   A special '0' value indicates the time source is unreliable and we
0049      *   need to use something else. The currently published specification
0050      *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
0051      *   instead of '0' as the special value, see commit c35b82ef0294.
0052      * - ReferenceTime =
0053      *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
0054      * - READ ReferenceTscSequence again. In case its value has changed
0055      *   since our first reading we need to discard ReferenceTime and repeat
0056      *   the whole sequence as the hypervisor was updating the page in
0057      *   between.
0058      */
0059     do {
0060         sequence = READ_ONCE(tsc_pg->tsc_sequence);
0061         if (!sequence)
0062             return U64_MAX;
0063         /*
0064          * Make sure we read sequence before we read other values from
0065          * TSC page.
0066          */
0067         smp_rmb();
0068
0069         scale = READ_ONCE(tsc_pg->tsc_scale);
0070         offset = READ_ONCE(tsc_pg->tsc_offset);
0071         *cur_tsc = hv_get_raw_timer();
0072
0073         /*
0074          * Make sure we read sequence after we read all other values
0075          * from TSC page.
0076          */
0077         smp_rmb();
0078
0079     } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
0080
0081     return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
0082 }
0083
0084 static inline notrace u64
0085 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
0086 {
0087     u64 cur_tsc;
0088
0089     return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
0090 }
0091
0092 #else /* CONFIG_HYPERV_TIMER */
0093 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
0094 {
0095     return NULL;
0096 }
0097
0098 static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
0099                        u64 *cur_tsc)
0100 {
0101     return U64_MAX;
0102 }
0103
0104 static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
0105 static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
0106 static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
0107 static inline void hv_stimer_global_cleanup(void) {}
0108 static inline void hv_stimer0_isr(void) {}
0109
0110 #endif /* CONFIG_HYPERV_TIMER */
0111
0112 #endif