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authorMaxime Ripard <mripard@kernel.org>2023-07-11 09:23:20 +0200
committerMaxime Ripard <mripard@kernel.org>2023-07-11 09:23:20 +0200
commit2f98e686ef59b5d19af5847d755798e2031bee3a (patch)
tree7b47919242853d088decf898ca79d6cda0d49381 /drivers/clocksource/hyperv_timer.c
parenta2848d08742c8e8494675892c02c0d22acbe3cf8 (diff)
parent06c2afb862f9da8dc5efa4b6076a0e48c3fbaaa5 (diff)
downloadlwn-2f98e686ef59b5d19af5847d755798e2031bee3a.tar.gz
lwn-2f98e686ef59b5d19af5847d755798e2031bee3a.zip
Merge v6.5-rc1 into drm-misc-fixes
Boris needs 6.5-rc1 in drm-misc-fixes to prevent a conflict. Signed-off-by: Maxime Ripard <mripard@kernel.org>
Diffstat (limited to 'drivers/clocksource/hyperv_timer.c')
-rw-r--r--drivers/clocksource/hyperv_timer.c96
1 files changed, 49 insertions, 47 deletions
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index bcd9042a0c9f..e56307a81f4d 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -365,6 +365,20 @@ void hv_stimer_global_cleanup(void)
}
EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
+static __always_inline u64 read_hv_clock_msr(void)
+{
+ /*
+ * Read the partition counter to get the current tick count. This count
+ * is set to 0 when the partition is created and is incremented in 100
+ * nanosecond units.
+ *
+ * Use hv_raw_get_register() because this function is used from
+ * noinstr. Notable; while HV_REGISTER_TIME_REF_COUNT is a synthetic
+ * register it doesn't need the GHCB path.
+ */
+ return hv_raw_get_register(HV_REGISTER_TIME_REF_COUNT);
+}
+
/*
* Code and definitions for the Hyper-V clocksources. Two
* clocksources are defined: one that reads the Hyper-V defined MSR, and
@@ -393,14 +407,20 @@ 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 __always_inline 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 = read_hv_clock_msr();
- return current_tick;
+ return time;
}
static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)
@@ -408,7 +428,7 @@ static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)
return read_hv_clock_tsc();
}
-static u64 notrace read_hv_sched_clock_tsc(void)
+static u64 noinstr read_hv_sched_clock_tsc(void)
{
return (read_hv_clock_tsc() - hv_sched_clock_offset) *
(NSEC_PER_SEC / HV_CLOCK_HZ);
@@ -460,30 +480,14 @@ static struct clocksource hyperv_cs_tsc = {
#endif
};
-static u64 notrace read_hv_clock_msr(void)
-{
- /*
- * Read the partition counter to get the current tick count. This count
- * is set to 0 when the partition is created and is incremented in
- * 100 nanosecond units.
- */
- return hv_get_register(HV_REGISTER_TIME_REF_COUNT);
-}
-
static u64 notrace read_hv_clock_msr_cs(struct clocksource *arg)
{
return read_hv_clock_msr();
}
-static u64 notrace read_hv_sched_clock_msr(void)
-{
- return (read_hv_clock_msr() - hv_sched_clock_offset) *
- (NSEC_PER_SEC / HV_CLOCK_HZ);
-}
-
static struct clocksource hyperv_cs_msr = {
.name = "hyperv_clocksource_msr",
- .rating = 500,
+ .rating = 495,
.read = read_hv_clock_msr_cs,
.mask = CLOCKSOURCE_MASK(64),
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
@@ -513,7 +517,7 @@ static __always_inline void hv_setup_sched_clock(void *sched_clock)
static __always_inline void hv_setup_sched_clock(void *sched_clock) {}
#endif /* CONFIG_GENERIC_SCHED_CLOCK */
-static bool __init hv_init_tsc_clocksource(void)
+static void __init hv_init_tsc_clocksource(void)
{
union hv_reference_tsc_msr tsc_msr;
@@ -524,17 +528,14 @@ static bool __init hv_init_tsc_clocksource(void)
* Hyper-V Reference TSC rating, causing the generic TSC to be used.
* TSC_INVARIANT is not offered on ARM64, so the Hyper-V Reference
* TSC will be preferred over the virtualized ARM64 arch counter.
- * While the Hyper-V MSR clocksource won't be used since the
- * Reference TSC clocksource is present, change its rating as
- * well for consistency.
*/
if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
hyperv_cs_tsc.rating = 250;
- hyperv_cs_msr.rating = 250;
+ hyperv_cs_msr.rating = 245;
}
if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
- return false;
+ return;
hv_read_reference_counter = read_hv_clock_tsc;
@@ -565,33 +566,34 @@ static bool __init hv_init_tsc_clocksource(void)
clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
- hv_sched_clock_offset = hv_read_reference_counter();
- hv_setup_sched_clock(read_hv_sched_clock_tsc);
-
- return true;
+ /*
+ * If TSC is invariant, then let it stay as the sched clock since it
+ * will be faster than reading the TSC page. But if not invariant, use
+ * the TSC page so that live migrations across hosts with different
+ * frequencies is handled correctly.
+ */
+ if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT)) {
+ hv_sched_clock_offset = hv_read_reference_counter();
+ hv_setup_sched_clock(read_hv_sched_clock_tsc);
+ }
}
void __init hv_init_clocksource(void)
{
/*
- * Try to set up the TSC page clocksource. If it succeeds, we're
- * done. Otherwise, set up the MSR clocksource. At least one of
- * these will always be available except on very old versions of
- * Hyper-V on x86. In that case we won't have a Hyper-V
+ * Try to set up the TSC page clocksource, then the MSR clocksource.
+ * At least one of these will always be available except on very old
+ * versions of Hyper-V on x86. In that case we won't have a Hyper-V
* clocksource, but Linux will still run with a clocksource based
* on the emulated PIT or LAPIC timer.
+ *
+ * Never use the MSR clocksource as sched clock. It's too slow.
+ * Better to use the native sched clock as the fallback.
*/
- if (hv_init_tsc_clocksource())
- return;
-
- if (!(ms_hyperv.features & HV_MSR_TIME_REF_COUNT_AVAILABLE))
- return;
-
- hv_read_reference_counter = read_hv_clock_msr;
- clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
+ hv_init_tsc_clocksource();
- hv_sched_clock_offset = hv_read_reference_counter();
- hv_setup_sched_clock(read_hv_sched_clock_msr);
+ if (ms_hyperv.features & HV_MSR_TIME_REF_COUNT_AVAILABLE)
+ clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);
}
void __init hv_remap_tsc_clocksource(void)