[Qemu-devel] [PATCH v4 1/2] x86/cpu: Add support for UMONITOR/UMWAIT/TPAUSE

[Tao Xu]

UMONITOR, UMWAIT and TPAUSE are a set of user wait instructions.
This patch adds support for user wait instructions in KVM. Availability
of the user wait instructions is indicated by the presence of the CPUID
feature flag WAITPKG CPUID.0x07.0x0:ECX[5]. User wait instructions may
be executed at any privilege level, and use IA32_UMWAIT_CONTROL MSR to
set the maximum time.

The patch enable the umonitor, umwait and tpause features in KVM.
Because umwait and tpause can put a (psysical) CPU into a power saving
state, by default we dont't expose it to kvm and enable it only when
guest CPUID has it. And use QEMU command-line "-overcommit cpu-pm=on"
(enable_cpu_pm is enabled), a VM can use UMONITOR, UMWAIT and TPAUSE
instructions. If the instruction causes a delay, the amount of time
delayed is called here the physical delay. The physical delay is first
computed by determining the virtual delay (the time to delay relative to
the VM’s timestamp counter). Otherwise, UMONITOR, UMWAIT and TPAUSE cause
an invalid-opcode exception(#UD).

The release document ref below link:
https://software.intel.com/sites/default/files/\
managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf

Co-developed-by: Jingqi Liu <address@hidden>
Signed-off-by: Jingqi Liu <address@hidden>
Signed-off-by: Tao Xu <address@hidden>
---

No changes in v4.
---
 target/i386/cpu.c | 3 ++-
 target/i386/cpu.h | 1 +
 target/i386/kvm.c | 4 ++++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 805ce95247..9546a40d8a 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1061,7 +1061,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = 
{
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
             NULL, "avx512vbmi", "umip", "pku",
-            NULL /* ospke */, NULL, "avx512vbmi2", NULL,
+            NULL /* ospke */, "waitpkg", "avx512vbmi2", NULL,
             "gfni", "vaes", "vpclmulqdq", "avx512vnni",
             "avx512bitalg", NULL, "avx512-vpopcntdq", NULL,
             "la57", NULL, NULL, NULL,
@@ -5193,6 +5193,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
**errp)
             host_cpuid(5, 0, &cpu->mwait.eax, &cpu->mwait.ebx,
                        &cpu->mwait.ecx, &cpu->mwait.edx);
             env->features[FEAT_1_ECX] |= CPUID_EXT_MONITOR;
+            env->features[FEAT_7_0_ECX] |= CPUID_7_0_ECX_WAITPKG;
         }
     }
 
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 05393cf9d1..19caf82729 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -672,6 +672,7 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define CPUID_7_0_ECX_UMIP     (1U << 2)
 #define CPUID_7_0_ECX_PKU      (1U << 3)
 #define CPUID_7_0_ECX_OSPKE    (1U << 4)
+#define CPUID_7_0_ECX_WAITPKG  (1U << 5) /* UMONITOR/UMWAIT/TPAUSE 
Instructions */
 #define CPUID_7_0_ECX_VBMI2    (1U << 6) /* Additional VBMI Instrs */
 #define CPUID_7_0_ECX_GFNI     (1U << 8)
 #define CPUID_7_0_ECX_VAES     (1U << 9)
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index ec7870c6af..f8daa13f10 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -390,6 +390,10 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, 
uint32_t function,
         if (host_tsx_blacklisted()) {
             ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE);
         }
+    } else if (function == 7 && index == 0 && reg == R_ECX) {
+        if (enable_cpu_pm) {
+            ret |= CPUID_7_0_ECX_WAITPKG;
+        }
     } else if (function == 7 && index == 0 && reg == R_EDX) {
         /*
          * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts.
-- 
2.20.1