KVM: Handle cpuid in the kernel instead of punting to userspace

KVM used to handle cpuid by letting userspace decide what values to
return to the guest.  We now handle cpuid completely in the kernel.  We
still let userspace decide which values the guest will see by having
userspace set up the value table beforehand (this is necessary to allow
management software to set the cpu features to the least common denominator,
so that live migration can work).

The motivation for the change is that kvm kernel code can be impacted by
cpuid features, for example the x86 emulator.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 69 insertions, 0 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index ff8bcfee76e..caec54fbf07 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -1504,6 +1504,43 @@ void save_msrs(struct vmx_msr_entry *e, int n)
 }
 EXPORT_SYMBOL_GPL(save_msrs);
 
+void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
+{
+	int i;
+	u32 function;
+	struct kvm_cpuid_entry *e, *best;
+
+	kvm_arch_ops->cache_regs(vcpu);
+	function = vcpu->regs[VCPU_REGS_RAX];
+	vcpu->regs[VCPU_REGS_RAX] = 0;
+	vcpu->regs[VCPU_REGS_RBX] = 0;
+	vcpu->regs[VCPU_REGS_RCX] = 0;
+	vcpu->regs[VCPU_REGS_RDX] = 0;
+	best = NULL;
+	for (i = 0; i < vcpu->cpuid_nent; ++i) {
+		e = &vcpu->cpuid_entries[i];
+		if (e->function == function) {
+			best = e;
+			break;
+		}
+		/*
+		 * Both basic or both extended?
+		 */
+		if (((e->function ^ function) & 0x80000000) == 0)
+			if (!best || e->function > best->function)
+				best = e;
+	}
+	if (best) {
+		vcpu->regs[VCPU_REGS_RAX] = best->eax;
+		vcpu->regs[VCPU_REGS_RBX] = best->ebx;
+		vcpu->regs[VCPU_REGS_RCX] = best->ecx;
+		vcpu->regs[VCPU_REGS_RDX] = best->edx;
+	}
+	kvm_arch_ops->decache_regs(vcpu);
+	kvm_arch_ops->skip_emulated_instruction(vcpu);
+}
+EXPORT_SYMBOL_GPL(kvm_emulate_cpuid);
+
 static void complete_pio(struct kvm_vcpu *vcpu)
 {
 	struct kvm_io *io = &vcpu->run->io;
@@ -2075,6 +2112,26 @@ out:
 	return r;
 }
 
+static int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
+				    struct kvm_cpuid *cpuid,
+				    struct kvm_cpuid_entry __user *entries)
+{
+	int r;
+
+	r = -E2BIG;
+	if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
+		goto out;
+	r = -EFAULT;
+	if (copy_from_user(&vcpu->cpuid_entries, entries,
+			   cpuid->nent * sizeof(struct kvm_cpuid_entry)))
+		goto out;
+	vcpu->cpuid_nent = cpuid->nent;
+	return 0;
+
+out:
+	return r;
+}
+
 static long kvm_vcpu_ioctl(struct file *filp,
 			   unsigned int ioctl, unsigned long arg)
 {
@@ -2181,6 +2238,18 @@ static long kvm_vcpu_ioctl(struct file *filp,
 	case KVM_SET_MSRS:
 		r = msr_io(vcpu, argp, do_set_msr, 0);
 		break;
+	case KVM_SET_CPUID: {
+		struct kvm_cpuid __user *cpuid_arg = argp;
+		struct kvm_cpuid cpuid;
+
+		r = -EFAULT;
+		if (copy_from_user(&cpuid, cpuid_arg, sizeof cpuid))
+			goto out;
+		r = kvm_vcpu_ioctl_set_cpuid(vcpu, &cpuid, cpuid_arg->entries);
+		if (r)
+			goto out;
+		break;
+	}
 	default:
 		;
 	}