6.10-stable review patch. If anyone has any objections, please let me know.
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From: Dexuan Cui decui@microsoft.com
commit 7f828d5fff7d24752e1ecf6bebb6617a81f97b93 upstream.
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: Roman Kisel romank@linux.microsoft.com Signed-off-by: Dexuan Cui decui@microsoft.com Reviewed-by: Michael Kelley mhklinux@outlook.com Link: https://lore.kernel.org/r/20240621061614.8339-1-decui@microsoft.com Signed-off-by: Wei Liu wei.liu@kernel.org Message-ID: 20240621061614.8339-1-decui@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/mshyperv.c | 16 +++++++++++++++- drivers/clocksource/hyperv_timer.c | 16 +++++++++++++++- 2 files changed, 30 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -449,9 +449,23 @@ static void __init ms_hyperv_init_platfo 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;
--- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c @@ -137,7 +137,21 @@ static int hv_stimer_init(unsigned int c 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;