kvm: take a reference to GuestMemory in Vcpu

Logically, each VCPU is using GuestMemory, which holds a ref count to
the underlying memory mappings. This change formalizes this by giving an
actual reference of GuestMemory to each Vcpu struct.

This change is needed because the Vm can go out of scope and clean up
its reference, but the Vcpus may still be running, triggering an EFAULT
and a lot of confused days spent debugging.

TEST=With the unwind panic handler, trigger a panic right after the
     final vcpu thread barrier. If the VCPU threads do not complain
     about EFAULT (errno 14), this change worked.
BUG=None

Change-Id: I6289147de0adde61c81630357701487937b17ade
Reviewed-on: https://chromium-review.googlesource.com/1441355
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/kvm/src/lib.rs b/kvm/src/lib.rs
index 17d5a74..a9f2e8a 100644
--- a/kvm/src/lib.rs
+++ b/kvm/src/lib.rs
@@ -990,6 +990,7 @@ pub enum VcpuExit {
 pub struct Vcpu {
     vcpu: File,
     run_mmap: MemoryMapping,
+    guest_mem: GuestMemory,
 }
 
 impl Vcpu {
@@ -1012,7 +1013,21 @@ impl Vcpu {
         let run_mmap =
             MemoryMapping::from_fd(&vcpu, run_mmap_size).map_err(|_| Error::new(ENOSPC))?;
 
-        Ok(Vcpu { vcpu, run_mmap })
+        let guest_mem = vm.guest_mem.clone();
+
+        Ok(Vcpu {
+            vcpu,
+            run_mmap,
+            guest_mem,
+        })
+    }
+
+    /// Gets a reference to the guest memory owned by this VM of this VCPU.
+    ///
+    /// Note that `GuestMemory` does not include any device memory that may have been added after
+    /// this VM was constructed.
+    pub fn get_memory(&self) -> &GuestMemory {
+        &self.guest_mem
     }
 
     /// Sets the data received by an mmio or ioport read/in instruction.