Maybe no contract ... but a bunch of places (many of them in Intel specific code) that check for it
Interestingly, quite a few of them are actually checking for HYPERVISOR not because of missing hypervisor features, but rather because hypervisors don't have to work around certain errata. :)
Full analysis after my sig, but tl;dr: the only case of using HYPERVISOR before using MSRs are in arch/x86/events/intel/cstate.c and arch/x86/events/intel/uncore.c. There are some workarounds in drivers/gpu that might fall into a similar bucket. But as far as MSRs go, the way to go overwhelmingly seems to be {rd,wr}msrl_safe.
Thanks, Paolo On 10/11/20 00:36, Luck, Tony wrote:
arch/x86/events/core.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
Print a slightly less frightening warning.
arch/x86/events/intel/core.c: if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
Working around KVM's ignore_msrs=1 option (and quite ugly; shows that the option shouldn't be enabled by default).
arch/x86/events/intel/core.c: int assume = 3 * !boot_cpu_has(X86_FEATURE_HYPERVISOR);
Seems unnecessary.
arch/x86/events/intel/cstate.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) arch/x86/events/intel/uncore.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
Too complicated. :)
arch/x86/kernel/apic/apic.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
Hypervisors don't have errata.
arch/x86/kernel/cpu/bugs.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
arch/x86/kernel/cpu/bugs.c: else if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
arch/x86/kernel/cpu/bugs.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
arch/x86/kernel/cpu/bugs.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
arch/x86/kernel/cpu/intel.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
Print different vulnerability status in sysfs.
arch/x86/kernel/cpu/mshyperv.c: if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
arch/x86/kernel/cpu/vmware.c: * If !boot_cpu_has(X86_FEATURE_HYPERVISOR), vmware_hypercall_mode
arch/x86/kernel/cpu/vmware.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
arch/x86/kernel/jailhouse.c: !boot_cpu_has(X86_FEATURE_HYPERVISOR))
arch/x86/kernel/kvm.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
arch/x86/kernel/paravirt.c: if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
Obviously needed before using paravirt features of the hypervisor.
arch/x86/kernel/tsc.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR) ||
Disables ART in VMs. Probably the idea is that ART does not have an offset field similar to the TSC's, but it's not necessary. Looking at the hypervisor-provided CPUID should be enough.
arch/x86/mm/init_64.c: if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
Tweaks hotplug heuristics, no MSRs involved.
drivers/acpi/processor_idle.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
Avoids pointless hypervisor exit on idle (i.e. just an optimization).
drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h: return boot_cpu_has(X86_FEATURE_HYPERVISOR);
Work around SR-IOV bugs.
drivers/gpu/drm/i915/i915_memcpy.c: !boot_cpu_has(X86_FEATURE_HYPERVISOR))
Work around KVM deficiency.
drivers/gpu/drm/radeon/radeon_device.c: return boot_cpu_has(X86_FEATURE_HYPERVISOR);
Work around SR-IOV bugs.
drivers/visorbus/visorchipset.c: if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
Needed before using paravirt features of the hypervisor.
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