[Qemu-devel] [PATCH] expose paravirt feature list to cpuid

[Qemu-devel] [PATCH] expose paravirt feature list to cpuid

[Glauber Costa]

Expose the paravirt features provided by the host to the guest.
The features exposed uses qemu just as a medium, since they only
depend on a negotiation between the host and guest directly.

As a direct result, we're now able to run the kvm pvclock in qemu
based kvm guests.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 kvm.h             |    1 +
 target-i386/kvm.c |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/kvm.h b/kvm.h
index efce145..db58baa 100644
--- a/kvm.h
+++ b/kvm.h
@@ -17,6 +17,7 @@
 #include "config.h"
 
 #ifdef CONFIG_KVM
+#include <linux/kvm_para.h>
 extern int kvm_allowed;
 
 #define kvm_enabled() (kvm_allowed)
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 2412ae4..3c62df5 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -33,6 +33,35 @@
     do { } while (0)
 #endif
 
+struct kvm_para_features {
+    int cap;
+    int feature;
+} para_features[] = {
+#ifdef KVM_CAP_CLOCKSOURCE
+	{ KVM_CAP_CLOCKSOURCE, KVM_FEATURE_CLOCKSOURCE },
+#endif
+#ifdef KVM_CAP_NOP_IO_DELAY
+	{ KVM_CAP_NOP_IO_DELAY, KVM_FEATURE_NOP_IO_DELAY },
+#endif
+#ifdef KVM_CAP_PV_MMU
+	{ KVM_CAP_PV_MMU, KVM_FEATURE_MMU_OP },
+#endif
+#ifdef KVM_CAP_CR3_CACHE
+	{ KVM_CAP_CR3_CACHE, KVM_FEATURE_CR3_CACHE },
+#endif
+};
+
+static int get_para_features(CPUState *env)
+{
+    int i, features = 0;
+
+    for (i = 0; i < ARRAY_SIZE(para_features); i++) {
+        if (kvm_ioctl(env->kvm_state, KVM_CHECK_EXTENSION, para_features[i].cap))
+            features |= (1 << para_features[i].feature);
+    }
+
+    return features;
+}
 int kvm_arch_init_vcpu(CPUState *env)
 {
     struct {
@@ -41,8 +70,29 @@ int kvm_arch_init_vcpu(CPUState *env)
     } __attribute__((packed)) cpuid_data;
     uint32_t limit, i, cpuid_i;
     uint32_t eax, ebx, ecx, edx;
+#ifdef KVM_CPUID_SIGNATURE
+    struct kvm_cpuid_entry *pv_ent;
+    uint32_t signature[3];
+#endif
 
     cpuid_i = 0;
+#ifdef KVM_CPUID_SIGNATURE
+    /* Paravirtualization CPUIDs */
+    memcpy(signature, "KVMKVMKVM\0\0\0", 12);
+    pv_ent = &cpuid_data.entries[cpuid_i++];
+    memset(pv_ent, 0, sizeof(*pv_ent));
+    pv_ent->function = KVM_CPUID_SIGNATURE;
+    pv_ent->eax = 0;
+    pv_ent->ebx = signature[0];
+    pv_ent->ecx = signature[1];
+    pv_ent->edx = signature[2];
+
+    pv_ent = &cpuid_data.entries[cpuid_i++];
+    memset(pv_ent, 0, sizeof(*pv_ent));
+    pv_ent->function = KVM_CPUID_FEATURES;
+    pv_ent->eax = get_para_features(env);
+#endif
+
 
     cpu_x86_cpuid(env, 0, &eax, &ebx, &ecx, &edx);
     limit = eax;
-- 
1.5.6.5

Re: [Qemu-devel] [PATCH] expose paravirt feature list to cpuid

[Paul Brook]

> +#ifdef KVM_CPUID_SIGNATURE
> +    /* Paravirtualization CPUIDs */
> +    memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> +    pv_ent->ebx = signature[0];
> +    pv_ent->ecx = signature[1];
> +    pv_ent->edx = signature[2];

This is broken on big-endian hosts.

I realise this code is currently only enabled for x86 hosts, however there's a 
good chance we'll want to implement something similar for normal qemu. At 
minimum it needs a comment saying that it's potentially broken.

Paul