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f8d0186a26
Adds three recommendation bits to CPUID 0x40000004.EAX so Windows /
Hyper-V-aware guests use the corresponding paravirtualized hypercalls
instead of falling back to architectural primitives. The hypercalls
themselves are emulated unconditionally by KVM and surfaced via the
corresponding KVM_CAP_HYPERV_* info caps; no userspace cap negotiation
is needed because KVM advertises support to the guest at hypercall
issue time:
KVM_CAP_HYPERV_TLBFLUSH advertises HvFlush{VirtualAddressSpace,Ex,
List,ListEx} (api.rst 8.18, info-only cap).
KVM_CAP_HYPERV_SEND_IPI advertises HvCallSendSyntheticClusterIpi{,Ex}
(api.rst 8.20, also info-only).
Leaf 0x40000004.EAX (HV_CPUID_ENLIGHTMENT_INFO):
bit 1 LocalTlbFlushRecommended
bit 2 RemoteTlbFlushRecommended
Recommend HvFlushVirtualAddressSpace / List in place of
architectural INVPCID / INVLPG broadcasts. Remote shoot-down
via hypercall lets the host skip vCPUs that are not currently
scheduled, instead of waiting for an IPI ack.
bit 10 ClusterIpiRecommended
Recommend HvCallSendSyntheticClusterIpi over per-target APIC
ICR writes. A single hypercall can target up to 64 vCPUs (or
all of them via the Ex variant) versus one VM exit per APIC
access on the architectural path.
These bits depend on AccessVpIndex (0x40000003.EAX bit 6), which is
advertised by the partition-privileges change.
Sources:
Microsoft Hypervisor Top-Level Functional Specification 7.4.5
qemu/qemu docs/system/i386/hyperv.rst (hv-tlbflush, hv-ipi)
Linux Documentation/virt/kvm/api.rst 8.18, 8.20
Signed-off-by: CMGS <ilskdw@gmail.com>