[PATCH 3/4] target/i386: Add getting RAPSIZE for ERAPS enabled guests

[Ben Cheatham <Benjamin.Cheatham@amd.com>]

From: Amit Shah <amit.shah@amd.com>

Newer AMD CPUs have the ERAPS (Enhanced Return Address Predictor
Security) cpuid bit. When this bit is available, the size of the RSB is
indicated in EBX bits 16:23 of the same function. Allow the guest to use
these features when kvm is enabled and are available on the host.

NOTE: The commit description is from a patch made by Amit while the
actual changes are a subset of that patch, hence my Co-developed-by.
Amit, let me know if the attribution looks good to you.

Signed-off-by: Amit Shah <amit.shah@amd.com>
Co-developed-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
---
 target/i386/cpu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index a85cc67700fa..9342cc3ca4c6 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -9292,7 +9292,13 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
     case 0x80000021:
         *eax = *ebx = *ecx = *edx = 0;
         *eax = env->features[FEAT_8000_0021_EAX];
-        *ebx = env->features[FEAT_8000_0021_EBX];
+
+        if (kvm_enabled() && (*eax & CPUID_8000_0021_EAX_ERAPS)) {
+            *ebx |=
+              kvm_arch_get_supported_cpuid(cs->kvm_state, index, count, R_EBX) &
+              CPUID_8000_0021_EBX_RAPSIZE;
+        }
+
         *ecx = env->features[FEAT_8000_0021_ECX];
         break;
     case 0x80000022:
-- 
2.53.0