From: Jim Mattson <jmattson@google.com>
Date: Wed, 25 Sep 2019 11:17:14 -0700
Subject: kvm: x86: Fix a spurious -E2BIG in __do_cpuid_func
Git-commit: a1a640b8c0cd8a2a7f84ab694f04bc64dc6988af
Patch-mainline: v5.4-rc2
References: bsc#1164345

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>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kvm/cpuid.c | 16 ++++++++++------
 1 file 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;
 		}