kvm: x86: Fix a spurious -E2BIG in __do_cpuid_func

Don't return -E2BIG from __do_cpuid_func when processing function 0BH
or 1FH and the last interesting subleaf occupies the last allocated
entry in the result array.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Fixes: 831bf664e9c1fc ("KVM: Refactor and simplify kvm_dev_ioctl_get_supported_cpuid")
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 63316036f85a..6bf4a261b308 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -618,16 +618,20 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
          */
         case 0x1f:
         case 0xb: {
-                int i, level_type;
+                int i;
 
-                /* read more entries until level_type is zero */
-                for (i = 1; ; ++i) {
+                /*
+                 * We filled in entry[0] for CPUID(EAX=<function>,
+                 * ECX=00H) above.  If its level type (ECX[15:8]) is
+                 * zero, then the leaf is unimplemented, and we're
+                 * done.  Otherwise, continue to populate entries
+                 * until the level type (ECX[15:8]) of the previously
+                 * added entry is zero.
+                 */
+                for (i = 1; entry[i - 1].ecx & 0xff00; ++i) {
                         if (*nent >= maxnent)
                                 goto out;
 
-                        level_type = entry[i - 1].ecx & 0xff00;
-                        if (!level_type)
-                                break;
                         do_host_cpuid(&entry[i], function, i);
                         ++*nent;
                 }