[PULL 17/30] i386: Support KVM_CAP_ENFORCE_PV_FEATURE_CPUID

[Paolo Bonzini]

From: Vitaly Kuznetsov <vkuznets@redhat.com>

By default, KVM allows the guest to use all currently supported PV features
even when they were not announced in guest visible CPUIDs. Introduce a new
"kvm-pv-enforce-cpuid" flag to limit the supported feature set to the
exposed features. The feature is supported by Linux >= 5.10 and is not
enabled by default in QEMU.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210902093530.345756-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/cpu.c     |  2 ++
 target/i386/cpu.h     |  3 +++
 target/i386/kvm/kvm.c | 10 ++++++++++
 3 files changed, 15 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index cacec605bf..598019de12 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6860,6 +6860,8 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("l3-cache", X86CPU, enable_l3_cache, true),
     DEFINE_PROP_BOOL("kvm-no-smi-migration", X86CPU, kvm_no_smi_migration,
                      false),
+    DEFINE_PROP_BOOL("kvm-pv-enforce-cpuid", X86CPU, kvm_pv_enforce_cpuid,
+                     false),
     DEFINE_PROP_BOOL("vmware-cpuid-freq", X86CPU, vmware_cpuid_freq, true),
     DEFINE_PROP_BOOL("tcg-cpuid", X86CPU, expose_tcg, true),
     DEFINE_PROP_BOOL("x-migrate-smi-count", X86CPU, migrate_smi_count,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 29552dc2a7..c990150373 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1802,6 +1802,9 @@ struct X86CPU {
     /* Stop SMI delivery for migration compatibility with old machines */
     bool kvm_no_smi_migration;
 
+    /* Forcefully disable KVM PV features not exposed in guest CPUIDs */
+    bool kvm_pv_enforce_cpuid;
+
     /* Number of physical address bits supported */
     uint32_t phys_bits;
 
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 7f1b060e6d..d6a70c27e5 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1629,6 +1629,16 @@ int kvm_arch_init_vcpu(CPUState *cs)
 
     cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
 
+    if (cpu->kvm_pv_enforce_cpuid) {
+        r = kvm_vcpu_enable_cap(cs, KVM_CAP_ENFORCE_PV_FEATURE_CPUID, 0, 1);
+        if (r < 0) {
+            fprintf(stderr,
+                    "failed to enable KVM_CAP_ENFORCE_PV_FEATURE_CPUID: %s",
+                    strerror(-r));
+            abort();
+        }
+    }
+
     for (i = 0; i <= limit; i++) {
         if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
             fprintf(stderr, "unsupported level value: 0x%x\n", limit);
-- 
2.31.1