[PATCH 1/4] target/i386: add support for FRED in CPUID enumeration

[Xin Li <xin3.li@intel.com>]

FRED, i.e., the Intel flexible return and event delivery architecture,
defines simple new transitions that change privilege level (ring
transitions).

In addition to these transitions, the FRED architecture defines a new
instruction (LKGS) for managing the state of the GS segment register.
The LKGS instruction can be used by 64-bit operating systems that do
not use the new FRED transitions.

The CPUID feature flag CPUID.(EAX=7,ECX=1):EAX[17] enumerates FRED, and
the CPUID feature flag CPUID.(EAX=7,ECX=1):EAX[18] enumerates LKGS.

Add CPUID definitions for FRED/LKGS, and expose them to KVM guests only.

Because FRED relies on LKGS, add it to feature dependency map.

Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 target/i386/cpu.c | 6 +++++-
 target/i386/cpu.h | 4 ++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 00f913b638..3dba6b46d9 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -963,7 +963,7 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
             "avx-vnni", "avx512-bf16", NULL, "cmpccxadd",
             NULL, NULL, "fzrm", "fsrs",
             "fsrc", NULL, NULL, NULL,
-            NULL, NULL, NULL, NULL,
+            NULL, "fred", "lkgs", NULL,
             NULL, "amx-fp16", NULL, "avx-ifma",
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
@@ -1549,6 +1549,10 @@ static FeatureDep feature_dependencies[] = {
         .from = { FEAT_VMX_SECONDARY_CTLS,  VMX_SECONDARY_EXEC_ENABLE_USER_WAIT_PAUSE },
         .to = { FEAT_7_0_ECX,               CPUID_7_0_ECX_WAITPKG },
     },
+    {
+        .from = { FEAT_7_1_EAX,             CPUID_7_1_EAX_LKGS },
+        .to = { FEAT_7_1_EAX,               CPUID_7_1_EAX_FRED },
+    },
 };
 
 typedef struct X86RegisterInfo32 {
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index a6000e93bd..064decbc85 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -932,6 +932,10 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
 #define CPUID_7_1_EDX_AVX_NE_CONVERT    (1U << 5)
 /* PREFETCHIT0/1 Instructions */
 #define CPUID_7_1_EDX_PREFETCHITI       (1U << 14)
+/* Flexible return and event delivery (FRED) */
+#define CPUID_7_1_EAX_FRED              (1U << 17)
+/* Load into IA32_KERNEL_GS_BASE (LKGS) */
+#define CPUID_7_1_EAX_LKGS              (1U << 18)
 
 /* Do not exhibit MXCSR Configuration Dependent Timing (MCDT) behavior */
 #define CPUID_7_2_EDX_MCDT_NO           (1U << 5)
-- 
2.34.1