From: Dexuan Cui <[email protected]> Sent: Thursday, June 20, 2024 11:16 PM > > 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: [email protected] # 6.6+ > Reviewed-by: Roman Kisel <[email protected]> > Signed-off-by: Dexuan Cui <[email protected]> > --- > > 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
Reviewed-by: Michael Kelley <[email protected]>
