KVM: Split cpuid register access from computation

Introduce kvm_cpuid() to perform the leaf limit check and calculate
register values, and let kvm_emulate_cpuid() just handle reading and
writing the registers from/to the vcpu.  This allows us to reuse
kvm_cpuid() in a context where directly reading and writing registers
is not desired.

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

1 files changed, 22 insertions, 18 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 61ccbdf3d0ac..197afd53e3a4 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -640,33 +640,37 @@ static struct kvm_cpuid_entry2* check_cpuid_limit(struct kvm_vcpu *vcpu,
         return kvm_find_cpuid_entry(vcpu, maxlevel->eax, index);
 }
 
-void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
+void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
 {
-        u32 function, index;
+        u32 function = *eax, index = *ecx;
         struct kvm_cpuid_entry2 *best;
 
-        function = kvm_register_read(vcpu, VCPU_REGS_RAX);
-        index = kvm_register_read(vcpu, VCPU_REGS_RCX);
-        kvm_register_write(vcpu, VCPU_REGS_RAX, 0);
-        kvm_register_write(vcpu, VCPU_REGS_RBX, 0);
-        kvm_register_write(vcpu, VCPU_REGS_RCX, 0);
-        kvm_register_write(vcpu, VCPU_REGS_RDX, 0);
         best = kvm_find_cpuid_entry(vcpu, function, index);
 
         if (!best)
                 best = check_cpuid_limit(vcpu, function, index);
 
         if (best) {
-                kvm_register_write(vcpu, VCPU_REGS_RAX, best->eax);
-                kvm_register_write(vcpu, VCPU_REGS_RBX, best->ebx);
-                kvm_register_write(vcpu, VCPU_REGS_RCX, best->ecx);
-                kvm_register_write(vcpu, VCPU_REGS_RDX, best->edx);
-        }
+                *eax = best->eax;
+                *ebx = best->ebx;
+                *ecx = best->ecx;
+                *edx = best->edx;
+        } else
+                *eax = *ebx = *ecx = *edx = 0;
+}
+
+void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
+{
+        u32 function, eax, ebx, ecx, edx;
+
+        function = eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
+        ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
+        kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);
+        kvm_register_write(vcpu, VCPU_REGS_RAX, eax);
+        kvm_register_write(vcpu, VCPU_REGS_RBX, ebx);
+        kvm_register_write(vcpu, VCPU_REGS_RCX, ecx);
+        kvm_register_write(vcpu, VCPU_REGS_RDX, edx);
         kvm_x86_ops->skip_emulated_instruction(vcpu);
-        trace_kvm_cpuid(function,
-                        kvm_register_read(vcpu, VCPU_REGS_RAX),
-                        kvm_register_read(vcpu, VCPU_REGS_RBX),
-                        kvm_register_read(vcpu, VCPU_REGS_RCX),
-                        kvm_register_read(vcpu, VCPU_REGS_RDX));
+        trace_kvm_cpuid(function, eax, ebx, ecx, edx);
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_cpuid);