support mmap shared

Author: CompuIves

Cargo.lock

@@ -596,6 +596,19 @@
                     }
                 ]
             },
+            {
+                "syscall": "msync",
+                "comment": "Used to sync memory from mmap to disk",
+                "args": [
+                    {
+                        "index": 2,
+                        "type": "dword",
+                        "op": "eq",
+                        "val": 4,
+                        "comment": "MS_SYNC"
+                    }
+                ]
+            },
             {
                 "syscall": "rt_sigaction",
                 "comment": "rt_sigaction is used by libc::abort during a panic to install the default handler for SIGABRT",

resources/seccomp/aarch64-unknown-linux-musl.json

@@ -248,6 +248,19 @@
                     }
                 ]
             },
+            {
+                "syscall": "msync",
+                "comment": "Used to sync memory from mmap to disk",
+                "args": [
+                    {
+                        "index": 2,
+                        "type": "dword",
+                        "op": "eq",
+                        "val": 4,
+                        "comment": "MS_SYNC"
+                    }
+                ]
+            },
             {
                 "syscall": "rt_sigaction",
                 "comment": "rt_sigaction is used by libc::abort during a panic to install the default handler for SIGABRT",

resources/seccomp/x86_64-unknown-linux-musl.json

@@ -116,7 +116,7 @@ pub fn create_guest_memory(
     for region in regions {
         let flags = match region.0 {
             None => libc::MAP_NORESERVE | libc::MAP_PRIVATE | libc::MAP_ANONYMOUS,
-            Some(_) => libc::MAP_NORESERVE | libc::MAP_PRIVATE,
+            Some(_) => libc::MAP_NORESERVE | libc::MAP_SHARED,
         };
 
         let mmap_region =

src/vm-memory/src/lib.rs

@@ -16,7 +16,7 @@ use arch::regs::{get_manufacturer_id_from_host, get_manufacturer_id_from_state};
 #[cfg(target_arch = "x86_64")]
 use cpuid::common::{get_vendor_id_from_cpuid, get_vendor_id_from_host};
 use devices::virtio::TYPE_NET;
-use logger::{error, info};
+use logger::{error, info, warn};
 use seccompiler::BpfThreadMap;
 use serde::Serialize;
 use snapshot::Snapshot;
@@ -25,7 +25,7 @@ use utils::sock_ctrl_msg::ScmSocket;
 use versionize::{VersionMap, Versionize, VersionizeResult};
 use versionize_derive::Versionize;
 use virtio_gen::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
-use vm_memory::{GuestMemory, GuestMemoryMmap};
+use vm_memory::{GuestMemory, GuestMemoryMmap, GuestMemoryRegion};
 
 use crate::builder::{self, StartMicrovmError};
 use crate::device_manager::persist::{DeviceStates, Error as DevicePersistError};
@@ -324,6 +324,25 @@ fn snapshot_memory_to_file(
     mem_file_path: &Path,
     snapshot_type: &SnapshotType,
 ) -> std::result::Result<(), CreateSnapshotError> {
+    if OpenOptions::new().read(true).open(mem_file_path).is_ok() {
+        // The memory file already exists.
+        // We're going to use the msync behaviour
+        for region in vmm.guest_memory().iter() {
+            warn!("saving memory region");
+            unsafe {
+                if libc::msync(region.as_ptr() as _, region.len() as _, libc::MS_SYNC) == -1 {
+                    return Err(CreateSnapshotError::Memory(
+                        memory_snapshot::Error::CreateRegion(vm_memory::MmapRegionError::Mmap(
+                            std::io::Error::last_os_error(),
+                        )),
+                    ));
+                }
+            };
+        }
+
+        return Ok(());
+    }
+
     use self::CreateSnapshotError::*;
     let mut file = OpenOptions::new()
         .write(true)
@@ -552,7 +571,11 @@ fn guest_memory_from_file(
     track_dirty_pages: bool,
 ) -> std::result::Result<GuestMemoryMmap, LoadSnapshotError> {
     use self::LoadSnapshotError::{DeserializeMemory, MemoryBackingFile};
-    let mem_file = File::open(mem_file_path).map_err(MemoryBackingFile)?;
+    let mem_file = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .open(mem_file_path)
+        .map_err(MemoryBackingFile)?;
     GuestMemoryMmap::restore(Some(&mem_file), mem_state, track_dirty_pages)
         .map_err(DeserializeMemory)
 }