diff mbox series

[v1,3/3] target/i386: Add the immediate form MSR access instruction support

Message ID 20250103084827.1820007-4-xin@zytor.com (mailing list archive)
State New
Headers show
Series target/i386: Add the immediate form MSR access instruction support | expand

Commit Message

Xin Li (Intel) Jan. 3, 2025, 8:48 a.m. UTC 
The immediate form of MSR access instructions are primarily motivated by
performance, not code size: by having the MSR number in an immediate, it
is available *much* earlier in the pipeline, which allows the hardware
much more leeway about how a particular MSR is handled.

Signed-off-by: Xin Li (Intel) <xin@zytor.com>
---
 target/i386/cpu.c | 2 +-
 target/i386/cpu.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2fb05879c3..83fb059d09 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1138,7 +1138,7 @@  FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
             NULL, NULL, NULL, NULL,
-            NULL, NULL, NULL, NULL,
+            NULL, "msr-imm", NULL, NULL,
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index d23fa96549..df27c359d3 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -987,6 +987,9 @@  uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w);
 /* Non-Serializing Write to Model Specific Register (WRMSRNS) */
 #define CPUID_7_1_EAX_WRMSRNS           (1U << 19)
 
+/* The immediate form of MSR access instructions */
+#define CPUID_7_1_ECX_MSR_IMM           (1U << 5)
+
 /* Do not exhibit MXCSR Configuration Dependent Timing (MCDT) behavior */
 #define CPUID_7_2_EDX_MCDT_NO           (1U << 5)