From: "Xin Li (Intel)" <x...@zytor.com> 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) <x...@zytor.com> Link: https://lore.kernel.org/r/20250103084827.1820007-4-...@zytor.com Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> --- target/i386/cpu.h | 4 ++++ target/i386/cpu.c | 2 +- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/target/i386/cpu.h b/target/i386/cpu.h index 0ec1cbd9f43..545851cbde1 100644 --- a/target/i386/cpu.h +++ b/target/i386/cpu.h @@ -1001,6 +1001,9 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w); /* Linear Address Masking */ #define CPUID_7_1_EAX_LAM (1U << 26) +/* The immediate form of MSR access instructions */ +#define CPUID_7_1_ECX_MSR_IMM (1U << 5) + /* Support for VPDPB[SU,UU,SS]D[,S] */ #define CPUID_7_1_EDX_AVX_VNNI_INT8 (1U << 4) /* AVX NE CONVERT Instructions */ @@ -1024,6 +1027,7 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w); #define CPUID_7_2_EDX_DDPD_U (1U << 3) /* Indicate bit 10 of the IA32_SPEC_CTRL MSR is supported */ #define CPUID_7_2_EDX_BHI_CTRL (1U << 4) + /* Do not exhibit MXCSR Configuration Dependent Timing (MCDT) behavior */ #define CPUID_7_2_EDX_MCDT_NO (1U << 5) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index b05f465e2ef..40aefb38f6d 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -1155,7 +1155,7 @@ 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, -- 2.49.0
