Commit 7f828d5f authored by Dexuan Cui's avatar Dexuan Cui Committed by Wei Liu
Browse files

clocksource: hyper-v: Use lapic timer in a TDX VM without paravisor 



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@vger.kernel.org # 6.6+
Reviewed-by: default avatarRoman Kisel <romank@linux.microsoft.com>
Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
Reviewed-by: default avatarMichael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20240621061614.8339-1-decui@microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
Message-ID: <20240621061614.8339-1-decui@microsoft.com>
parent 90ac806c

arch/x86/kernel/cpu/mshyperv.c

+15 −1
Original line number Diff line number Diff line
@@ -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;

drivers/clocksource/hyperv_timer.c

+15 −1
Original line number Diff line number Diff line
@@ -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);



	/*

	 * 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;