[PATCH] whpx: i386: workaround for Windows 10 support

[Mohamed Mediouni <mohamed@unpredictable.fr>]

Windows Server 2022 and later support
WHvCapabilityCodeProcessorPerfmonFeatures and
WHvPartitionPropertyCodeSyntheticProcessorFeaturesBanks.

Windows 10 supports neither of those.

As the QEMU executable doesn't have a manifest, OS version
queries do not return the actual Windows version but 6.2.9200
which corresponds to Windows 8. Windows Server 2022 and Windows
11 still use the 10.0 number, with distinction being the build
number.

As such, use the absence of perf monitoring feature query as
a cutoff to detect if a legacy OS is present.

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
---
 target/i386/whpx/whpx-all.c | 43 ++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/target/i386/whpx/whpx-all.c b/target/i386/whpx/whpx-all.c
index 4d5d3dbd24..015c0f1dc9 100644
--- a/target/i386/whpx/whpx-all.c
+++ b/target/i386/whpx/whpx-all.c
@@ -1948,6 +1948,7 @@ int whpx_accel_init(AccelState *as, MachineState *ms)
     WHV_CAPABILITY_FEATURES features = {0};
     WHV_PROCESSOR_FEATURES_BANKS processor_features;
     WHV_PROCESSOR_PERFMON_FEATURES perfmon_features;
+    bool is_legacy_os = false;
 
     whpx = &whpx_global;
 
@@ -2096,21 +2097,29 @@ int whpx_accel_init(AccelState *as, MachineState *ms)
     hr = whp_dispatch.WHvGetCapability(
         WHvCapabilityCodeProcessorPerfmonFeatures, &perfmon_features,
         sizeof(WHV_PROCESSOR_PERFMON_FEATURES), &whpx_cap_size);
+    /*
+     * Relying on this is a crutch to maintain Windows 10 support.
+     *
+     * WHvCapabilityCodeProcessorPerfmonFeatures and
+     * WHvPartitionPropertyCodeSyntheticProcessorFeaturesBanks
+     * are implemented starting from Windows Server 2022 (build 20348).
+     */
     if (FAILED(hr)) {
-        error_report("WHPX: Failed to get performance monitoring features, hr=%08lx", hr);
-        ret = -ENOSPC;
-        goto error;
-    }
-
-    hr = whp_dispatch.WHvSetPartitionProperty(
-            whpx->partition,
-            WHvPartitionPropertyCodeProcessorPerfmonFeatures,
-            &perfmon_features,
-            sizeof(WHV_PROCESSOR_PERFMON_FEATURES));
-    if (FAILED(hr)) {
-        error_report("WHPX: Failed to set performance monitoring features, hr=%08lx", hr);
-        ret = -EINVAL;
-        goto error;
+        warn_report("WHPX: Failed to get performance "
+                    "monitoring features, hr=%08lx", hr);
+        is_legacy_os = true;
+    } else {
+        hr = whp_dispatch.WHvSetPartitionProperty(
+                whpx->partition,
+                WHvPartitionPropertyCodeProcessorPerfmonFeatures,
+                &perfmon_features,
+                sizeof(WHV_PROCESSOR_PERFMON_FEATURES));
+        if (FAILED(hr)) {
+            error_report("WHPX: Failed to set performance "
+                         "monitoring features, hr=%08lx", hr);
+            ret = -EINVAL;
+            goto error;
+        }
     }
 
     /* Enable synthetic processor features */
@@ -2138,7 +2147,7 @@ int whpx_accel_init(AccelState *as, MachineState *ms)
         synthetic_features.Bank0.DirectSyntheticTimers = 1;
     }
 
-    if (whpx->hyperv_enlightenments_allowed) {
+    if (!is_legacy_os && whpx->hyperv_enlightenments_allowed) {
         hr = whp_dispatch.WHvSetPartitionProperty(
                 whpx->partition,
                 WHvPartitionPropertyCodeSyntheticProcessorFeaturesBanks,
@@ -2149,6 +2158,10 @@ int whpx_accel_init(AccelState *as, MachineState *ms)
             ret = -EINVAL;
             goto error;
         }
+    } else if (is_legacy_os && whpx->hyperv_enlightenments_required) {
+        error_report("Hyper-V enlightenments not available on legacy Windows");
+        ret = -EINVAL;
+        goto error;
     }
 
     /* Register for MSR and CPUID exits */
-- 
2.50.1 (Apple Git-155)