From f795081bf9badb4d0ca6b74e65d35c8836331a18 Mon Sep 17 00:00:00 2001
From: Muminul Islam <muislam@microsoft.com>
Date: Thu, 4 Dec 2025 18:35:43 -0800
Subject: [PATCH] hypervisor: mshv: retrieve MSRs list correctly
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The MSR enumeration logic in MSHV does not accurately
account for the capabilities of the underlying
hardware and hypervisor. Previously, integration tests
passed because only the default MSRs—universally supported
across platforms—were involved. However, recent feature
additions in MSHV have introduced MSRs that are not
supported on Intel hardware, causing failures.

This patch retrieves the MSRs from the VM specific
API call that filters out the unsupported MSRs.

Signed-off-by: Muminul Islam <muislam@microsoft.com>
---
 hypervisor/src/mshv/mod.rs | 53 +++++++++++++++++---------------------
 hypervisor/src/vm.rs       |  6 +++++
 2 files changed, 30 insertions(+), 29 deletions(-)

diff --git a/hypervisor/src/mshv/mod.rs b/hypervisor/src/mshv/mod.rs
index 90173d011..40d8796e9 100644
--- a/hypervisor/src/mshv/mod.rs
+++ b/hypervisor/src/mshv/mod.rs
@@ -10,6 +10,10 @@ use std::num::NonZeroUsize;
 use std::sync::{Arc, RwLock};
 
 use anyhow::anyhow;
+#[cfg(target_arch = "x86_64")]
+use arc_swap::ArcSwap;
+#[cfg(feature = "sev_snp")]
+use log::info;
 use log::{debug, warn};
 use mshv_bindings::*;
 #[cfg(target_arch = "x86_64")]
@@ -22,8 +26,6 @@ use vfio_ioctls::VfioDeviceFd;
 use vm::DataMatch;
 #[cfg(feature = "sev_snp")]
 use vm_memory::bitmap::AtomicBitmap;
-#[cfg(feature = "sev_snp")]
-use {arc_swap::ArcSwap, log::info};
 
 #[cfg(target_arch = "aarch64")]
 use crate::arch::aarch64::regs::{
@@ -219,18 +221,6 @@ pub struct MshvHypervisor {
     mshv: Mshv,
 }
 
-impl MshvHypervisor {
-    #[cfg(target_arch = "x86_64")]
-    ///
-    /// Retrieve the list of MSRs supported by MSHV.
-    ///
-    fn get_msr_list(&self) -> hypervisor::Result<Vec<u32>> {
-        self.mshv
-            .get_msr_index_list()
-            .map_err(|e| hypervisor::HypervisorError::GetMsrList(e.into()))
-    }
-}
-
 impl MshvHypervisor {
     /// Create a hypervisor based on Mshv
     #[allow(clippy::new_ret_no_self)]
@@ -348,20 +338,9 @@ impl hypervisor::Hypervisor for MshvHypervisor {
 
         #[cfg(target_arch = "x86_64")]
         {
-            let msr_list = self.get_msr_list()?;
-            let mut msrs: Vec<MsrEntry> = vec![
-                MsrEntry {
-                    ..Default::default()
-                };
-                msr_list.len()
-            ];
-            for (pos, index) in msr_list.iter().enumerate() {
-                msrs[pos].index = *index;
-            }
-
             Ok(Arc::new(MshvVm {
                 fd: vm_fd,
-                msrs,
+                msrs: ArcSwap::new(Vec::<MsrEntry>::new().into()),
                 dirty_log_slots: Arc::new(RwLock::new(HashMap::new())),
                 #[cfg(feature = "sev_snp")]
                 sev_snp_enabled: mshv_vm_type == VmType::Snp,
@@ -1713,7 +1692,7 @@ impl MshvVcpu {
 pub struct MshvVm {
     fd: Arc<VmFd>,
     #[cfg(target_arch = "x86_64")]
-    msrs: Vec<MsrEntry>,
+    msrs: ArcSwap<Vec<MsrEntry>>,
     dirty_log_slots: Arc<RwLock<HashMap<u64, MshvDirtyLogSlot>>>,
     #[cfg(feature = "sev_snp")]
     sev_snp_enabled: bool,
@@ -1845,7 +1824,7 @@ impl vm::Vm for MshvVm {
             #[cfg(target_arch = "x86_64")]
             cpuid: Vec::new(),
             #[cfg(target_arch = "x86_64")]
-            msrs: self.msrs.clone(),
+            msrs: self.msrs.load().as_ref().clone(),
             vm_ops,
             vm_fd: self.fd.clone(),
             #[cfg(feature = "sev_snp")]
@@ -2454,7 +2433,23 @@ impl vm::Vm for MshvVm {
                 1u64,
             )
             .map_err(|e| vm::HypervisorVmError::InitializeVm(e.into()))?;
-
+        #[cfg(target_arch = "x86_64")]
+        {
+            let msr_list = self
+                .fd
+                .get_msr_index_list()
+                .map_err(|e| vm::HypervisorVmError::GetMsrList(e.into()))?;
+            let mut msrs: Vec<MsrEntry> = vec![
+                MsrEntry {
+                    ..Default::default()
+                };
+                msr_list.len()
+            ];
+            for (pos, index) in msr_list.iter().enumerate() {
+                msrs[pos].index = *index;
+            }
+            self.msrs.store(Arc::new(msrs));
+        }
         Ok(())
     }
 }
diff --git a/hypervisor/src/vm.rs b/hypervisor/src/vm.rs
index 5b56923b1..9d7e60a8b 100644
--- a/hypervisor/src/vm.rs
+++ b/hypervisor/src/vm.rs
@@ -257,6 +257,12 @@ pub enum HypervisorVmError {
     ///
     #[error("Failed to initialize VM")]
     InitializeVm(#[source] anyhow::Error),
+    #[cfg(all(target_arch = "x86_64", feature = "mshv"))]
+    ///
+    /// Failed to retrieve list of MSRs.
+    ///
+    #[error("Failed to get the list of supported MSRs")]
+    GetMsrList(#[source] anyhow::Error),
 }
 ///
 /// Result type for returning from a function