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target/i386: Add the immediate form MSR access instruction support

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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>
Link: https://lore.kernel.org/r/20250103084827.1820007-4-xin@zytor.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Xin Li (Intel) 2025-01-03 00:48:27 -08:00 • committed by Paolo Bonzini
parent 99216748fd
commit 91084f3b44
2 changed files with 5 additions and 1 deletions
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2
target/i386/cpu.c
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@ -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,

4
target/i386/cpu.h
View file

@ -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)