i386/kvm: handle Xen HVM cpuid leaves

Introduce support for emulating CPUID for Xen HVM guests. It doesn't make
sense to advertise the KVM leaves to a Xen guest, so do Xen unconditionally
when the xen-version machine property is set.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
[dwmw2: Obtain xen_version from KVM property, make it automatic]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

target/i386/cpu.c

@@ -7200,6 +7200,7 @@ static Property x86_cpu_properties[] = {
      * own cache information (see x86_cpu_load_def()).
      */
     DEFINE_PROP_BOOL("legacy-cache", X86CPU, legacy_cache, true),
+    DEFINE_PROP_BOOL("xen-vapic", X86CPU, xen_vapic, false),
 
     /*
      * From "Requirements for Implementing the Microsoft

target/i386/cpu.h

@@ -1975,6 +1975,8 @@ struct ArchCPU {
     int32_t thread_id;
 
     int32_t hv_max_vps;
+
+    bool xen_vapic;
 };
 
 

target/i386/kvm/kvm.c

@@ -22,6 +22,7 @@
 
 #include <linux/kvm.h>
 #include "standard-headers/asm-x86/kvm_para.h"
+#include "hw/xen/interface/arch-x86/cpuid.h"
 
 #include "cpu.h"
 #include "host-cpu.h"
@@ -1819,7 +1820,77 @@ int kvm_arch_init_vcpu(CPUState *cs)
         has_msr_hv_hypercall = true;
     }
 
-    if (cpu->expose_kvm) {
+    if (cs->kvm_state->xen_version) {
+#ifdef CONFIG_XEN_EMU
+        struct kvm_cpuid_entry2 *xen_max_leaf;
+
+        memcpy(signature, "XenVMMXenVMM", 12);
+
+        xen_max_leaf = c = &cpuid_data.entries[cpuid_i++];
+        c->function = kvm_base + XEN_CPUID_SIGNATURE;
+        c->eax = kvm_base + XEN_CPUID_TIME;
+        c->ebx = signature[0];
+        c->ecx = signature[1];
+        c->edx = signature[2];
+
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = kvm_base + XEN_CPUID_VENDOR;
+        c->eax = cs->kvm_state->xen_version;
+        c->ebx = 0;
+        c->ecx = 0;
+        c->edx = 0;
+
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = kvm_base + XEN_CPUID_HVM_MSR;
+        /* Number of hypercall-transfer pages */
+        c->eax = 1;
+        /* Hypercall MSR base address */
+        if (hyperv_enabled(cpu)) {
+            c->ebx = XEN_HYPERCALL_MSR_HYPERV;
+            kvm_xen_init(cs->kvm_state, c->ebx);
+        } else {
+            c->ebx = XEN_HYPERCALL_MSR;
+        }
+        c->ecx = 0;
+        c->edx = 0;
+
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = kvm_base + XEN_CPUID_TIME;
+        c->eax = ((!!tsc_is_stable_and_known(env) << 1) |
+            (!!(env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_RDTSCP) << 2));
+        /* default=0 (emulate if necessary) */
+        c->ebx = 0;
+        /* guest tsc frequency */
+        c->ecx = env->user_tsc_khz;
+        /* guest tsc incarnation (migration count) */
+        c->edx = 0;
+
+        c = &cpuid_data.entries[cpuid_i++];
+        c->function = kvm_base + XEN_CPUID_HVM;
+        xen_max_leaf->eax = kvm_base + XEN_CPUID_HVM;
+        if (cs->kvm_state->xen_version >= XEN_VERSION(4, 5)) {
+            c->function = kvm_base + XEN_CPUID_HVM;
+
+            if (cpu->xen_vapic) {
+                c->eax |= XEN_HVM_CPUID_APIC_ACCESS_VIRT;
+                c->eax |= XEN_HVM_CPUID_X2APIC_VIRT;
+            }
+
+            c->eax |= XEN_HVM_CPUID_IOMMU_MAPPINGS;
+
+            if (cs->kvm_state->xen_version >= XEN_VERSION(4, 6)) {
+                c->eax |= XEN_HVM_CPUID_VCPU_ID_PRESENT;
+                c->ebx = cs->cpu_index;
+            }
+        }
+
+        kvm_base += 0x100;
+#else /* CONFIG_XEN_EMU */
+        /* This should never happen as kvm_arch_init() would have died first. */
+        fprintf(stderr, "Cannot enable Xen CPUID without Xen support\n");
+        abort();
+#endif
+    } else if (cpu->expose_kvm) {
         memcpy(signature, "KVMKVMKVM\0\0\0", 12);
         c = &cpuid_data.entries[cpuid_i++];
         c->function = KVM_CPUID_SIGNATURE | kvm_base;
@@ -2539,7 +2610,9 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
             error_report("kvm: Xen support only available in PC machine");
             return -ENOTSUP;
         }
-        ret = kvm_xen_init(s);
+        /* hyperv_enabled() doesn't work yet. */
+        uint32_t msr = XEN_HYPERCALL_MSR;
+        ret = kvm_xen_init(s, msr);
         if (ret < 0) {
             return ret;
         }

target/i386/kvm/xen-emu.c

@@ -15,12 +15,12 @@
 #include "kvm/kvm_i386.h"
 #include "xen-emu.h"
 
-int kvm_xen_init(KVMState *s)
+int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
 {
     const int required_caps = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
         KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL | KVM_XEN_HVM_CONFIG_SHARED_INFO;
     struct kvm_xen_hvm_config cfg = {
-        .msr = XEN_HYPERCALL_MSR,
+        .msr = hypercall_msr,
         .flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL,
     };
     int xen_caps, ret;

target/i386/kvm/xen-emu.h

@@ -12,8 +12,17 @@
 #ifndef QEMU_I386_KVM_XEN_EMU_H
 #define QEMU_I386_KVM_XEN_EMU_H
 
-#define XEN_HYPERCALL_MSR 0x40000000
+#define XEN_HYPERCALL_MSR               0x40000000
+#define XEN_HYPERCALL_MSR_HYPERV        0x40000200
 
-int kvm_xen_init(KVMState *s);
+#define XEN_CPUID_SIGNATURE        0
+#define XEN_CPUID_VENDOR           1
+#define XEN_CPUID_HVM_MSR          2
+#define XEN_CPUID_TIME             3
+#define XEN_CPUID_HVM              4
+
+#define XEN_VERSION(maj, min) ((maj) << 16 | (min))
+
+int kvm_xen_init(KVMState *s, uint32_t hypercall_msr);
 
 #endif /* QEMU_I386_KVM_XEN_EMU_H */