[PULL,01/27] target/i386: remove PCOMMIT from TCG, deprecate property

Commit Message

Paolo Bonzini May 12, 2024, 10:49 a.m. UTC

The PCOMMIT instruction was never included in any physical processor.
TCG implements it as a no-op instruction, but its utility is debatable
to say the least.  Drop it from the decoder since it is only available
with "-cpu max", which does not guarantee migration compatibility
across versions, and deprecate the property just in case someone is
using it as "pcommit=off".

Reviewed-by: Richard Henderson <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 docs/about/deprecated.rst   |  8 ++++++++
 target/i386/cpu.h           |  2 --
 target/i386/cpu.c           |  2 +-
 target/i386/tcg/translate.c | 12 +-----------
 4 files changed, 10 insertions(+), 14 deletions(-)

Patch

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 5c3ca47801f..40585ca7d55 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -432,6 +432,14 @@  Backend ``memory`` (since 9.0)
 CPU device properties
 '''''''''''''''''''''
 
+``pcommit`` on x86 (since 9.1)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The PCOMMIT instruction was never included in any physical processor.
+It was implemented as a no-op instruction in TCG up to QEMU 9.0, but
+only with ``-cpu max`` (which does not guarantee migration compatibility
+across versions).
+
 ``pmu-num=n`` on RISC-V CPUs (since 8.2)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 1e0d2c915f5..ccccb62fc35 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -816,8 +816,6 @@  uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
 #define CPUID_7_0_EBX_SMAP              (1U << 20)
 /* AVX-512 Integer Fused Multiply Add */
 #define CPUID_7_0_EBX_AVX512IFMA        (1U << 21)
-/* Persistent Commit */
-#define CPUID_7_0_EBX_PCOMMIT           (1U << 22)
 /* Flush a Cache Line Optimized */
 #define CPUID_7_0_EBX_CLFLUSHOPT        (1U << 23)
 /* Cache Line Write Back */
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1058b6803fd..79372de8c5a 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -713,7 +713,7 @@  void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
 #endif
 #define TCG_7_0_EBX_FEATURES (CPUID_7_0_EBX_SMEP | CPUID_7_0_EBX_SMAP | \
           CPUID_7_0_EBX_BMI1 | CPUID_7_0_EBX_BMI2 | CPUID_7_0_EBX_ADX | \
-          CPUID_7_0_EBX_PCOMMIT | CPUID_7_0_EBX_CLFLUSHOPT |            \
+          CPUID_7_0_EBX_CLFLUSHOPT |            \
           CPUID_7_0_EBX_CLWB | CPUID_7_0_EBX_MPX | CPUID_7_0_EBX_FSGSBASE | \
           CPUID_7_0_EBX_ERMS | CPUID_7_0_EBX_AVX2 | CPUID_7_0_EBX_RDSEED | \
           CPUID_7_0_EBX_SHA_NI | CPUID_7_0_EBX_KERNEL_FEATURES)
diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c
index 3842b294842..7d9f6b5c55b 100644
--- a/target/i386/tcg/translate.c
+++ b/target/i386/tcg/translate.c
@@ -4487,17 +4487,7 @@  static void disas_insn_old(DisasContext *s, CPUState *cpu, int b)
             }
             goto unknown_op;
 
-        case 0xf8: /* sfence / pcommit */
-            if (prefixes & PREFIX_DATA) {
-                /* pcommit */
-                if (!(s->cpuid_7_0_ebx_features & CPUID_7_0_EBX_PCOMMIT)
-                    || (prefixes & PREFIX_LOCK)) {
-                    goto illegal_op;
-                }
-                break;
-            }
-            /* fallthru */
-        case 0xf9 ... 0xff: /* sfence */
+        case 0xf8 ... 0xff: /* sfence */
             if (!(s->cpuid_features & CPUID_SSE)
                 || (prefixes & PREFIX_LOCK)) {
                 goto illegal_op;