[PATCH v4 4/5] target/i386: Add feature that indicates WRMSR to BASE reg is non-serializing

[Babu Moger <babu.moger@xxxxxxx>]

Add the CPUID bit indicates that a WRMSR to MSR_FS_BASE, MSR_GS_BASE, or
MSR_KERNEL_GS_BASE is non-serializing.

CPUID_Fn80000021_EAX
Bit    Feature description
1      FsGsKernelGsBaseNonSerializing.
       WRMSR to FS_BASE, GS_BASE and KernelGSbase are non-serializing.

Link: https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/programmer-references/57238.zip
Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
 target/i386/cpu.c | 2 +-
 target/i386/cpu.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 4a4e9b81d8..107ecd2bde 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1235,7 +1235,7 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
     [FEAT_8000_0021_EAX] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
-            "no-nested-data-bp", NULL, "lfence-always-serializing", NULL,
+            "no-nested-data-bp", "fs-gs-base-ns", "lfence-always-serializing", NULL,
             NULL, NULL, "null-sel-clr-base", NULL,
             "auto-ibrs", NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index b65eedb617..12dafc9b32 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1032,6 +1032,8 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w);
 
 /* Processor ignores nested data breakpoints */
 #define CPUID_8000_0021_EAX_NO_NESTED_DATA_BP            (1U << 0)
+/* WRMSR to FS_BASE, GS_BASE, or KERNEL_GS_BASE is non-serializing */
+#define CPUID_8000_0021_EAX_FS_GS_BASE_NS                (1U << 1)
 /* LFENCE is always serializing */
 #define CPUID_8000_0021_EAX_LFENCE_ALWAYS_SERIALIZING    (1U << 2)
 /* Null Selector Clears Base */
-- 
2.34.1