Minor enhancement and bugfixes

src/cap.rs

@@ -139,6 +139,8 @@ pub enum Cap {
     S390UserSigp = KVM_CAP_S390_USER_SIGP,
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     SplitIrqchip = KVM_CAP_SPLIT_IRQCHIP,
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    DisableExits = KVM_CAP_X86_DISABLE_EXITS,
     ImmediateExit = KVM_CAP_IMMEDIATE_EXIT,
     ArmVmIPASize = KVM_CAP_ARM_VM_IPA_SIZE,
     MsiDevid = KVM_CAP_MSI_DEVID,

src/ioctls/system.rs

@@ -213,9 +213,12 @@ impl Kvm {
     /// assert!(kvm.get_max_vcpus() > 0);
     /// ```
     pub fn get_max_vcpus(&self) -> usize {
-        match self.check_extension_int(Cap::MaxVcpus) {
-            0 => self.get_nr_vcpus(),
-            x => x as usize,
+        let v = self.check_extension_int(Cap::MaxVcpus);
+
+        if v <= 0 {
+            self.get_nr_vcpus()
+        } else {
+            v as usize
         }
     }
 
@@ -233,9 +236,38 @@ impl Kvm {
     /// assert!(kvm.get_max_vcpu_id() > 0);
     /// ```
     pub fn get_max_vcpu_id(&self) -> usize {
-        match self.check_extension_int(Cap::MaxVcpuId) {
-            0 => self.get_max_vcpus(),
-            x => x as usize,
+        let v = self.check_extension_int(Cap::MaxVcpuId);
+
+        if v <= 0 {
+            self.get_max_vcpus()
+        } else {
+            v as usize
+        }
+    }
+
+    /// Returns the "disable idle exiting" capability.
+    ///
+    /// The `KVM_CAP_X86_DISABLE_EXITS` capability provides userspace with per-VM capability
+    /// to not intercept MWAIT/HLT/PAUSE/CSTATE, which means though instructions won't cause
+    /// vm-exits and helps to improve latency in some workloads.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # extern crate kvm_bindings;
+    /// # use kvm_bindings::{KVM_X86_DISABLE_EXITS_HLT, KVM_X86_DISABLE_EXITS_PAUSE};
+    /// # use kvm_ioctls::Kvm;
+    /// let kvm = Kvm::new().unwrap();
+    /// assert!(kvm.get_disable_exits() & KVM_X86_DISABLE_EXITS_HLT != 0);
+    /// assert!(kvm.get_disable_exits() & KVM_X86_DISABLE_EXITS_PAUSE != 0);
+    /// ```
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    pub fn get_disable_exits(&self) -> u32 {
+        let x = self.check_extension_int(Cap::DisableExits);
+        if x > 0 {
+            x as u32
+        } else {
+            0
         }
     }
 
@@ -542,7 +574,9 @@ impl FromRawFd for Kvm {
 mod tests {
     use super::*;
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-    use kvm_bindings::KVM_MAX_CPUID_ENTRIES;
+    use kvm_bindings::{
+        KVM_MAX_CPUID_ENTRIES, KVM_X86_DISABLE_EXITS_HLT, KVM_X86_DISABLE_EXITS_PAUSE,
+    };
     use libc::{fcntl, FD_CLOEXEC, F_GETFD};
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     use vmm_sys_util::fam::FamStruct;
@@ -598,6 +632,18 @@ mod tests {
         assert!(kvm.get_nr_memslots() >= 32);
     }
 
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    #[test]
+    fn test_kvm_get_disable_exits() {
+        let kvm = Kvm::new().unwrap();
+        let disable_exits = kvm.get_disable_exits();
+
+        if disable_exits != 0 {
+            assert!(disable_exits & KVM_X86_DISABLE_EXITS_HLT != 0);
+            assert!(disable_exits & KVM_X86_DISABLE_EXITS_PAUSE != 0);
+        }
+    }
+
     #[test]
     fn test_create_vm() {
         let kvm = Kvm::new().unwrap();