In a TDX VM without paravisor, currently the default timer is the Hyper-V
timer, which depends on the slow VM Reference Counter MSR: the Hyper-V TSC
page is not enabled in such a VM because the VM uses Invariant TSC as a
better clocksource and it's challenging to mark the Hyper-V TSC page shared
in very early boot.
Lower the rating of the Hyper-V timer so the local APIC timer becomes the
the default timer in such a VM, and print a warning in case Invariant TSC
is unavailable in such a VM. This change should cause no perceivable
performance difference.
Cc: stable@xxxxxxxxxxxxxxx # 6.6+
Reviewed-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---
Changes in v2:
Improved the comments in ms_hyperv_init_platform() [Michael Kelley]
Added "print a warning in case Invariant TSC unavailable" in the changelog.
Added Roman's Reviewed-by.
arch/x86/kernel/cpu/mshyperv.c | 16 +++++++++++++++-
drivers/clocksource/hyperv_timer.c | 16 +++++++++++++++-
2 files changed, 30 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index e0fd57a8ba840..954b7cbfa2f02 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -449,9 +449,23 @@ static void __init ms_hyperv_init_platform(void)
ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
if (!ms_hyperv.paravisor_present) {
- /* To be supported: more work is required. */
+ /*
+ * Mark the Hyper-V TSC page feature as disabled
+ * in a TDX VM without paravisor so that the
+ * Invariant TSC, which is a better clocksource
+ * anyway, is used instead.
+ */
ms_hyperv.features &= ~HV_MSR_REFERENCE_TSC_AVAILABLE;
+ /*
+ * The Invariant TSC is expected to be available
+ * in a TDX VM without paravisor, but if not,
+ * print a warning message. The slower Hyper-V MSR-based
+ * Ref Counter should end up being the clocksource.
+ */
+ if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
+ pr_warn("Hyper-V: Invariant TSC is unavailable\n");
+
/* HV_MSR_CRASH_CTL is unsupported. */
ms_hyperv.misc_features &= ~HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE;
diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index b2a080647e413..99177835cadec 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -137,7 +137,21 @@ static int hv_stimer_init(unsigned int cpu)
ce->name = "Hyper-V clockevent";
ce->features = CLOCK_EVT_FEAT_ONESHOT;
ce->cpumask = cpumask_of(cpu);
- ce->rating = 1000;
+
+ /*
+ * Lower the rating of the Hyper-V timer in a TDX VM without paravisor,
+ * so the local APIC timer (lapic_clockevent) is the default timer in
+ * such a VM. The Hyper-V timer is not preferred in such a VM because
+ * it depends on the slow VM Reference Counter MSR (the Hyper-V TSC
+ * page is not enbled in such a VM because the VM uses Invariant TSC
+ * as a better clocksource and it's challenging to mark the Hyper-V
+ * TSC page shared in very early boot).
+ */
+ if (!ms_hyperv.paravisor_present && hv_isolation_type_tdx())
+ ce->rating = 90;
+ else
+ ce->rating = 1000;
+
ce->set_state_shutdown = hv_ce_shutdown;
ce->set_state_oneshot = hv_ce_set_oneshot;
ce->set_next_event = hv_ce_set_next_event;
--
2.25.1
