[v2,3/5] target/i386: Add a couple of feature bits in 8000_0008_EBX

Commit Message

Babu Moger Jan. 6, 2023, 6:56 p.m. UTC

Add the following feature bits.

amd-psfd : Predictive Store Forwarding Disable:
           PSF is a hardware-based micro-architectural optimization
           designed to improve the performance of code execution by
           predicting address dependencies between loads and stores.
           While SSBD (Speculative Store Bypass Disable) disables both
           PSF and speculative store bypass, PSFD only disables PSF.
           PSFD may be desirable for the software which is concerned
           with the speculative behavior of PSF but desires a smaller
           performance impact than setting SSBD.
	   Depends on the following kernel commit:
           b73a54321ad8 ("KVM: x86: Expose Predictive Store Forwarding Disable")

stibp-always-on :
           Single Thread Indirect Branch Prediction mode has enhanced
           performance and may be left always on.

The documentation for the features are available in the links below.
a. Processor Programming Reference (PPR) for AMD Family 19h Model 01h,
   Revision B1 Processors
b. SECURITY ANALYSIS OF AMD PREDICTIVE STORE FORWARDING

Link: https://www.amd.com/system/files/documents/security-analysis-predictive-store-forwarding.pdf
Link: https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip
Signed-off-by: Babu Moger <[e-mail]>
---
 target/i386/cpu.c | 4 ++--
 target/i386/cpu.h | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

Patch

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2dffd12081..117130fba1 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -909,10 +909,10 @@  FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
             NULL, NULL, NULL, NULL,
             NULL, "wbnoinvd", NULL, NULL,
             "ibpb", NULL, "ibrs", "amd-stibp",
-            NULL, NULL, NULL, NULL,
+            NULL, "stibp-always-on", NULL, NULL,
             NULL, NULL, NULL, NULL,
             "amd-ssbd", "virt-ssbd", "amd-no-ssb", NULL,
-            NULL, NULL, NULL, NULL,
+            "amd-psfd", NULL, NULL, NULL,
         },
         .cpuid = { .eax = 0x80000008, .reg = R_EBX, },
         .tcg_features = 0,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index d4bc19577a..8c65c92131 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -918,8 +918,12 @@  uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
 #define CPUID_8000_0008_EBX_IBRS        (1U << 14)
 /* Single Thread Indirect Branch Predictors */
 #define CPUID_8000_0008_EBX_STIBP       (1U << 15)
+/* STIBP mode has enhanced performance and may be left always on */
+#define CPUID_8000_0008_EBX_STIBP_ALWAYS_ON    (1U << 17)
 /* Speculative Store Bypass Disable */
 #define CPUID_8000_0008_EBX_AMD_SSBD    (1U << 24)
+/* Predictive Store Forwarding Disable */
+#define CPUID_8000_0008_EBX_AMD_PSFD    (1U << 28)
 
 #define CPUID_XSAVE_XSAVEOPT   (1U << 0)
 #define CPUID_XSAVE_XSAVEC     (1U << 1)