mshv-ioctls: check capability before using extended property

Signed-off-by: Muminul Islam <muislam@microsoft.com>

Author: russell-islam

mshv-ioctls/src/ioctls/system.rs

@@ -199,27 +199,39 @@ impl Mshv {
             feature_bits.set_synthetic_cluster_ipi(1);
             feature_bits.set_direct_synthetic_timers(1);
             feature_bits.set_access_vp_regs(1);
-            #[cfg(not(target_arch = "aarch64"))]
-            feature_bits.set_flush_guest_physical_address_space(1);
+
+            let vmm_caps = self.get_vmm_caps().unwrap();
+
+            if vmm_caps
+                .__bindgen_anon_1
+                .__bindgen_anon_1
+                .assignable_synthetic_proc_features()
+                == 1
+            {
+                #[cfg(not(target_arch = "aarch64"))]
+                feature_bits.set_flush_guest_physical_address_space(1);
+                // Intersect our default mask with the hypervisor-advertised set of
+                // assignable synthetic features. The property is in the extended range
+                // (0x00090xxx) and must be fetched via HVCALL_GET_PARTITION_PROPERTY_EX.
+                // The payload follows the banked property shape used by
+                // `hv_partition_property_vmm_capabilities`: u16 bank_count, three u16
+                // reserved words, then `bank_count` u64 masks. We use bank 0.
+                let assignable_ex = self
+                    .get_host_partition_property_ex(
+                        hv_partition_property_code_HV_PARTITION_PROPERTY_ASSIGNABLE_SYNTHETIC_PROC_FEATURES,
+                    )
+                    .unwrap();
+                // SAFETY: `hv_partition_property_ex` is a union whose `buffer` variant
+                // covers the full 4072-byte payload; reading the first bank u64 at
+                // offset 8 is within bounds.
+                let assignable_features: u64 =
+                    std::ptr::read_unaligned(assignable_ex.buffer.as_ptr().add(8) as *const u64);
+                // SAFETY: access union fields
+                features.as_uint64[0] & assignable_features
+            } else {
+                features.as_uint64[0]
+            }
         }
-        // Intersect our default mask with the hypervisor-advertised set of
-        // assignable synthetic features. The property is in the extended range
-        // (0x00090xxx) and must be fetched via HVCALL_GET_PARTITION_PROPERTY_EX.
-        // The payload follows the banked property shape used by
-        // `hv_partition_property_vmm_capabilities`: u16 bank_count, three u16
-        // reserved words, then `bank_count` u64 masks. We use bank 0.
-        let assignable_ex = self
-            .get_host_partition_property_ex(
-                hv_partition_property_code_HV_PARTITION_PROPERTY_ASSIGNABLE_SYNTHETIC_PROC_FEATURES,
-            )
-            .unwrap();
-        // SAFETY: `hv_partition_property_ex` is a union whose `buffer` variant
-        // covers the full 4072-byte payload; reading the first bank u64 at
-        // offset 8 is within bounds.
-        let assignable_features: u64 =
-            unsafe { std::ptr::read_unaligned(assignable_ex.buffer.as_ptr().add(8) as *const u64) };
-        // SAFETY: access union fields
-        unsafe { features.as_uint64[0] & assignable_features }
     }
 
     /// Helper function to creates a VM fd using the MSHV fd with provided configuration.
@@ -282,10 +294,10 @@ impl Mshv {
                 Ok(vmm_caps)
             }
             Err(MshvError::Hypercall {
-                status: Some(HvError::AccessDenied),
+                status: Some(HvError::AccessDenied | HvError::UnknownProperty),
                 ..
             }) => {
-                // If the hypercall fails with AccessDenied, it means the
+                // If the hypercall fails with AccessDenied or UnknownProperty, it means the
                 // VMM capabilities query is not supported on this MSHV version.
                 // As per the hypervisor team, we should treat this case as if
                 // none of the capabilities are set. So, return a zeroed out struct.