KVM: x86: export paravirtual cpuid flags in KVM_GET_SUPPORTED_CPUID

Right now, we were using individual KVM_CAP entities to communicate
userspace about which cpuids we support. This is suboptimal, since it
generates a delay between the feature arriving in the host, and
being available at the guest.

A much better mechanism is to list para features in KVM_GET_SUPPORTED_CPUID.
This makes userspace automatically aware of what we provide. And if we
ever add a new cpuid bit in the future, we have to do that again,
which create some complexity and delay in feature adoption.

Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 73d342c69ed4..419c4512e270 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1972,6 +1972,23 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
                 }
                 break;
         }
+        case KVM_CPUID_SIGNATURE: {
+                char signature[12] = "KVMKVMKVM\0\0";
+                u32 *sigptr = (u32 *)signature;
+                entry->eax = 0;
+                entry->ebx = sigptr[0];
+                entry->ecx = sigptr[1];
+                entry->edx = sigptr[2];
+                break;
+        }
+        case KVM_CPUID_FEATURES:
+                entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
+                             (1 << KVM_FEATURE_NOP_IO_DELAY) |
+                             (1 << KVM_FEATURE_CLOCKSOURCE2);
+                entry->ebx = 0;
+                entry->ecx = 0;
+                entry->edx = 0;
+                break;
         case 0x80000000:
                 entry->eax = min(entry->eax, 0x8000001a);
                 break;
@@ -2018,6 +2035,23 @@ static int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
         for (func = 0x80000001; func <= limit && nent < cpuid->nent; ++func)
                 do_cpuid_ent(&cpuid_entries[nent], func, 0,
                              &nent, cpuid->nent);
+
+
+
+        r = -E2BIG;
+        if (nent >= cpuid->nent)
+                goto out_free;
+
+        do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_SIGNATURE, 0, &nent,
+                     cpuid->nent);
+
+        r = -E2BIG;
+        if (nent >= cpuid->nent)
+                goto out_free;
+
+        do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_FEATURES, 0, &nent,
+                     cpuid->nent);
+
         r = -E2BIG;
         if (nent >= cpuid->nent)
                 goto out_free;