Add method to query KVM_CAP_X86_DISABLE_EXITS

Add method to query KVM_CAP_X86_DISABLE_EXITS for x86 platforms.

Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>

Author: jiangliu

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

@@ -239,6 +239,32 @@ impl Kvm {
         }
     }
 
+    /// 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
+        }
+    }
+
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     fn get_cpuid(&self, kind: u64, num_entries: usize) -> Result<CpuId> {
         if num_entries > KVM_MAX_CPUID_ENTRIES {
@@ -542,7 +568,9 @@ 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 +626,18 @@ 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();