hypervisor: vmm: mshv: Enable SMT for guests with threads_per_core > 1

Set HV_PARTITION_CREATION_FLAG_SMT_ENABLED_GUEST when the guest
topology has more than one thread per core. This allows the
hypervisor to schedule guest VPs correctly on SMT-enabled hosts.

Without this flag, the hypervisor schedules guest VPs incorrectly,
causing SMT unusable.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

hypervisor/src/lib.rs

@@ -171,6 +171,7 @@ pub struct HypervisorVmConfig {
     #[cfg(feature = "sev_snp")]
     pub mem_size: u64,
     pub nested: bool,
+    pub smt_enabled: bool,
 }
 
 #[derive(Copy, Clone)]

hypervisor/src/mshv/mod.rs

@@ -307,6 +307,10 @@ impl hypervisor::Hypervisor for MshvHypervisor {
                         .__bindgen_anon_1
                         .set_nested_virt_support(1u64);
                 }
+
+                if _config.smt_enabled {
+                    create_args.pt_flags |= 1 << MSHV_PT_BIT_SMT_ENABLED_GUEST;
+                }
             }
             // Modified feature bit fields are written back to create_args
             for i in 0..create_args.pt_num_cpu_fbanks {

vmm/src/lib.rs

@@ -221,6 +221,11 @@ impl From<&VmConfig> for hypervisor::HypervisorVmConfig {
             #[cfg(feature = "sev_snp")]
             mem_size: _value.memory.total_size(),
             nested: _value.cpus.nested,
+            smt_enabled: _value
+                .cpus
+                .topology
+                .as_ref()
+                .is_some_and(|t| t.threads_per_core > 1),
         }
     }
 }