Expose portable CPUID configuration for x86 machines

hypervisor/x86.go

@@ -2,6 +2,7 @@ package hypervisor
 
 import (
 	"context"
+
 	"j5.nz/cc/hypervisor/x86state"
 )
 
@@ -33,6 +34,10 @@ const (
 // The PC interrupt controllers and interval timer are provided by the backend.
 // Firmware, disk and display device semantics belong to the caller.
 type X86 interface {
+	// SupportedCPUID returns an owned table of accelerator-supported leaves.
+	SupportedCPUID() ([]x86state.CPUIDEntry, error)
+	// SetCPUID installs the machine's feature policy before the first Run.
+	SetCPUID([]x86state.CPUIDEntry) error
 	MapRAM(base, size uint64) ([]byte, error)
 	MapRAMRegions(size uint64, regions []RAMRegion) ([]byte, error)
 	Registers() (x86state.Registers, error)

hypervisor/x86state/cpuid.go

@@ -0,0 +1,7 @@
+package x86state
+
+// CPUIDEntry describes one architectural CPUID leaf and subleaf.
+type CPUIDEntry struct {
+	Function, Index, Flags uint32
+	Eax, Ebx, Ecx, Edx     uint32
+}

internal/hv/kvm/cpuid_linux_amd64.go

@@ -0,0 +1,39 @@
+//go:build linux && amd64
+
+package kvm
+
+import (
+	"fmt"
+
+	"j5.nz/cc/hypervisor/x86state"
+)
+
+// SupportedCPUID returns an owned copy of the features the accelerator can run.
+func (v *VM) SupportedCPUID() ([]x86state.CPUIDEntry, error) {
+	entries, err := getSupportedCPUID(v.kvm.fd)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]x86state.CPUIDEntry, 0, entries.Nr)
+	for _, e := range cpuidEntries(entries) {
+		result = append(result, x86state.CPUIDEntry{Function: e.Function, Index: e.Index, Flags: e.Flags, Eax: e.Eax, Ebx: e.Ebx, Ecx: e.Ecx, Edx: e.Edx})
+	}
+	return result, nil
+}
+
+// SetCPUID configures the single CPU before its first execution. Feature and
+// topology policy belongs to the machine model, not this accelerator boundary.
+func (v *VM) SetCPUID(entries []x86state.CPUIDEntry) error {
+	if len(v.vcpus) != 1 || len(entries) == 0 || len(entries) > cpuidMaxEntries {
+		return fmt.Errorf("invalid single-CPU CPUID table")
+	}
+	table, err := getSupportedCPUID(v.kvm.fd)
+	if err != nil {
+		return err
+	}
+	table.Nr = uint32(len(entries))
+	for i, e := range entries {
+		cpuidStorage(table)[i] = kvmCPUIDEntry2{Function: e.Function, Index: e.Index, Flags: e.Flags, Eax: e.Eax, Ebx: e.Ebx, Ecx: e.Ecx, Edx: e.Edx}
+	}
+	return setVCPUID(v.vcpufd, table)
+}