On 1/31/25 20:17, Sean Christopherson wrote:
> Add a "tsc_properties" set of flags and use it to annotate whether the
> TSC operates at a known and/or reliable frequency when registering a
> paravirtual TSC calibration routine. Currently, each PV flow manually
> sets the associated feature flags, but often in haphazard fashion that
> makes it difficult for unfamiliar readers to see the properties of the
> TSC when running under a particular hypervisor.
>
> The other, bigger issue with manually setting the feature flags is that
> it decouples the flags from the calibration routine. E.g. in theory, PV
> code could mark the TSC as having a known frequency, but then have its
> PV calibration discarded in favor of a method that doesn't use that known
> frequency. Passing the TSC properties along with the calibration routine
> will allow adding sanity checks to guard against replacing a "better"
> calibration routine with a "worse" routine.
>
> As a bonus, the flags also give developers working on new PV code a heads
> up that they should at least mark the TSC as having a known frequency.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/coco/sev/core.c | 6 ++----
> arch/x86/coco/tdx/tdx.c | 7 ++-----
> arch/x86/include/asm/tsc.h | 8 +++++++-
> arch/x86/kernel/cpu/acrn.c | 4 ++--
> arch/x86/kernel/cpu/mshyperv.c | 10 +++++++---
> arch/x86/kernel/cpu/vmware.c | 7 ++++---
> arch/x86/kernel/jailhouse.c | 4 ++--
> arch/x86/kernel/kvmclock.c | 4 ++--
> arch/x86/kernel/tsc.c | 8 +++++++-
> arch/x86/xen/time.c | 4 ++--
> 10 files changed, 37 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
> index d6f079a75f05..6e4a2053857c 100644
> --- a/arch/x86/kernel/cpu/vmware.c
> +++ b/arch/x86/kernel/cpu/vmware.c
> @@ -385,10 +385,10 @@ static void __init vmware_paravirt_ops_setup(void)
> */
> static void __init vmware_set_capabilities(void)
> {
> + /* TSC is non-stop and reliable even if the frequency isn't known. */
> setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC);
> setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
Should this line be deleted, too, or does the VMware flow require this
to be done separate from the tsc_register_calibration_routines() call?
Thanks,
Tom
> - if (vmware_tsc_khz)
> - setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> +
> if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL)
> setup_force_cpu_cap(X86_FEATURE_VMCALL);
> else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL)
> @@ -417,7 +417,8 @@ static void __init vmware_platform_setup(void)
>
> vmware_tsc_khz = tsc_khz;
> tsc_register_calibration_routines(vmware_get_tsc_khz,
> - vmware_get_tsc_khz);
> + vmware_get_tsc_khz,
> + TSC_FREQ_KNOWN_AND_RELIABLE);
>
> #ifdef CONFIG_X86_LOCAL_APIC
> /* Skip lapic calibration since we know the bus frequency. */
