vmm: prerequisites for accessing KVM_RUN in the vCPU loop

These are the prerequisites for the upcoming (quick and dirty)
solution to the problem that we might miss some events.

Author: phip1611

hypervisor/src/cpu.rs

@@ -10,6 +10,8 @@
 //
 //
 
+#[cfg(feature = "kvm")]
+use std::os::fd::RawFd;
 #[cfg(target_arch = "aarch64")]
 use std::sync::Arc;
 
@@ -602,4 +604,11 @@ pub trait Vcpu: Send + Sync {
     /// Trigger NMI interrupt
     ///
     fn nmi(&self) -> Result<()>;
+    /// Returns the underlying vCPU FD of KVM.
+    ///
+    /// # SAFETY
+    /// This is safe if we do only use this to map the KVM_RUN structure for the
+    /// signal handler and only use it from there.
+    #[cfg(feature = "kvm")]
+    unsafe fn get_kvm_vcpu_raw_fd(&self) -> RawFd;
 }

hypervisor/src/kvm/mod.rs

@@ -16,7 +16,7 @@ use std::collections::HashMap;
 use std::fs::File;
 #[cfg(target_arch = "x86_64")]
 use std::os::unix::io::AsRawFd;
-#[cfg(feature = "tdx")]
+#[cfg(any(feature = "tdx", feature = "kvm"))]
 use std::os::unix::io::RawFd;
 use std::result;
 #[cfg(target_arch = "x86_64")]
@@ -2769,6 +2769,13 @@ impl cpu::Vcpu for KvmVcpu {
         self.fd.lock().unwrap().set_kvm_immediate_exit(exit.into());
     }
 
+    #[cfg(feature = "kvm")]
+    unsafe fn get_kvm_vcpu_raw_fd(&self) -> RawFd {
+        let kvm_vcpu = self.fd.lock().unwrap();
+        let kvm_vcpu = &*kvm_vcpu;
+        kvm_vcpu.as_raw_fd()
+    }
+
     ///
     /// Returns the details about TDX exit reason
     ///

hypervisor/src/mshv/mod.rs

@@ -43,6 +43,7 @@ pub mod x86_64;
 pub mod aarch64;
 #[cfg(target_arch = "x86_64")]
 use std::fs::File;
+use std::os::fd::RawFd;
 use std::os::unix::io::AsRawFd;
 #[cfg(target_arch = "aarch64")]
 use std::sync::Mutex;
@@ -1576,6 +1577,11 @@ impl cpu::Vcpu for MshvVcpu {
 
         Ok(())
     }
+
+    #[cfg(feature = "kvm")]
+    unsafe fn get_kvm_vcpu_raw_fd(&self) -> RawFd {
+        todo!()
+    }
 }
 
 impl MshvVcpu {

vmm/src/cpu.rs

@@ -16,6 +16,8 @@ use std::collections::BTreeMap;
 use std::io::Write;
 #[cfg(all(target_arch = "x86_64", feature = "guest_debug"))]
 use std::mem::size_of;
+#[cfg(feature = "kvm")]
+use std::os::fd::RawFd;
 use std::os::unix::thread::JoinHandleExt;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Barrier, Mutex};
@@ -487,6 +489,12 @@ impl Vcpu {
             .map_err(Error::VcpuSetGicrBaseAddr)?;
         Ok(())
     }
+
+    #[cfg(feature = "kvm")]
+    pub fn get_kvm_vcpu_raw_fd(&self) -> RawFd {
+        // SAFETY: We hold onto the contract.
+        unsafe { self.vcpu.get_kvm_vcpu_raw_fd() }
+    }
 }
 
 impl Pausable for Vcpu {}