From a00189cf7278582e559b189967d0f262077a824b Mon Sep 17 00:00:00 2001
From: Anatol Belski <anbelski@linux.microsoft.com>
Date: Mon, 19 Jan 2026 19:15:12 +0100
Subject: [PATCH] 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      | 1 +
 hypervisor/src/mshv/mod.rs | 4 ++++
 vmm/src/lib.rs             | 5 +++++
 3 files changed, 10 insertions(+)

diff --git a/hypervisor/src/lib.rs b/hypervisor/src/lib.rs
index 77e1f9a43..7f8084d06 100644
--- a/hypervisor/src/lib.rs
+++ b/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)]
diff --git a/hypervisor/src/mshv/mod.rs b/hypervisor/src/mshv/mod.rs
index 0c8d2632c..b36b306a9 100644
--- a/hypervisor/src/mshv/mod.rs
+++ b/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 {
diff --git a/vmm/src/lib.rs b/vmm/src/lib.rs
index 6917e005e..41a2c3383 100644
--- a/vmm/src/lib.rs
+++ b/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),
         }
     }
 }