Add SET_LOG_BASE message support

If the backend has the VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol feature
it will receive the VHOST_USER_SET_LOG_BASE message with a file
descriptor of the dirty-pages log memory region. This log covers all
known guest addresses, and must be manipulated atomically.

For further info please see
https://qemu-project.gitlab.io/qemu/interop/vhost-user.html#migration

Signed-off-by: German Maglione <[email protected]>

Author: germag

vhost-user-backend/CHANGELOG.md

@@ -2,6 +2,7 @@
 ## [Unreleased]
 
 ### Added
+[#206](https://github.com/rust-vmm/vhost/pull/206) Add bitmap support for tracking dirty pages during migration
 
 ### Changed
 

vhost-user-backend/src/bitmap.rs

@@ -223,7 +223,6 @@ unsafe impl Send for MmapLogReg {}
 unsafe impl Sync for MmapLogReg {}
 
 impl MmapLogReg {
-    #![allow(dead_code)]
     // Note: We could try to adjust the mapping area to only cover the memory region, but
     // the region's starting address is not guarantee to be LOG_WORD_SIZE-page aligned
     // which makes the implementation needlessly cumbersome.

vhost-user-backend/src/handler.rs

@@ -6,17 +6,18 @@
 use std::error;
 use std::fs::File;
 use std::io;
+use std::os::fd::AsFd;
 #[cfg(feature = "postcopy")]
 use std::os::fd::FromRawFd;
 use std::os::unix::io::AsRawFd;
 use std::sync::Arc;
 use std::thread;
 
-use crate::bitmap::BitmapReplace;
+use crate::bitmap::{BitmapReplace, MemRegionBitmap, MmapLogReg};
 #[cfg(feature = "postcopy")]
 use userfaultfd::{Uffd, UffdBuilder};
 use vhost::vhost_user::message::{
-    VhostTransferStateDirection, VhostTransferStatePhase, VhostUserConfigFlags,
+    VhostTransferStateDirection, VhostTransferStatePhase, VhostUserConfigFlags, VhostUserLog,
     VhostUserMemoryRegion, VhostUserProtocolFeatures, VhostUserSingleMemoryRegion,
     VhostUserVirtioFeatures, VhostUserVringAddrFlags, VhostUserVringState,
 };
@@ -26,7 +27,10 @@ use vhost::vhost_user::{
 use virtio_bindings::bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
 use virtio_queue::{Error as VirtQueError, QueueT};
 use vm_memory::mmap::NewBitmap;
-use vm_memory::{GuestAddress, GuestAddressSpace, GuestMemoryMmap, GuestRegionMmap};
+use vm_memory::{
+    GuestAddress, GuestAddressSpace, GuestMemory, GuestMemoryMmap, GuestMemoryRegion,
+    GuestRegionMmap,
+};
 use vmm_sys_util::epoll::EventSet;
 
 use super::backend::VhostUserBackend;
@@ -712,6 +716,47 @@ where
         self.uffd = None;
         Ok(())
     }
+
+    // Sets logging (i.e., bitmap) shared memory space.
+    //
+    // During live migration, the front-end may need to track the modifications the back-end
+    // makes to the memory mapped regions. The front-end should mark the dirty pages in a log.
+    // Once it complies to this logging, it may declare the `VHOST_F_LOG_ALL` vhost feature.
+    //
+    // If the backend has the `VHOST_USER_PROTOCOL_F_LOG_SHMFD` protocol feature it may receive
+    // the `VHOST_USER_SET_LOG_BASE` message. The log memory file descriptor is provided in `file`,
+    // the size and offset of shared memory area are provided in the `VhostUserLog` message.
+    //
+    // See https://qemu-project.gitlab.io/qemu/interop/vhost-user.html#migration.
+    // TODO: We ignore the `LOG_ALL` flag on `SET_FEATURES`, so we will continue marking pages as
+    // dirty even if the migration fails. We need to disable the logging after receiving  a
+    // `SET_FEATURE` without the `LOG_ALL` flag.
+    fn set_log_base(&mut self, log: &VhostUserLog, file: File) -> VhostUserResult<()> {
+        let mem = self.atomic_mem.memory();
+
+        let logmem = Arc::new(
+            MmapLogReg::from_file(file.as_fd(), log.mmap_offset, log.mmap_size)
+                .map_err(VhostUserError::ReqHandlerError)?,
+        );
+
+        // Let's create all bitmaps first before replacing them, in case any of them fails
+        let mut bitmaps = Vec::new();
+        for region in mem.iter() {
+            let bitmap = <<T as VhostUserBackend>::Bitmap as BitmapReplace>::InnerBitmap::new(
+                region,
+                Arc::clone(&logmem),
+            )
+            .map_err(VhostUserError::ReqHandlerError)?;
+
+            bitmaps.push((region, bitmap));
+        }
+
+        for (region, bitmap) in bitmaps {
+            region.bitmap().replace(bitmap);
+        }
+
+        Ok(())
+    }
 }
 
 impl<T: VhostUserBackend> Drop for VhostUserHandler<T> {

vhost/CHANGELOG.md

@@ -2,6 +2,7 @@
 ## [Unreleased]
 
 ### Added
+[#206](https://github.com/rust-vmm/vhost/pull/206) Add bitmap support for tracking dirty pages during migration
 
 ### Changed
 

vhost/src/vhost_user/backend_req_handler.rs

@@ -83,6 +83,7 @@ pub trait VhostUserBackendReqHandler {
     fn postcopy_listen(&self) -> Result<()>;
     #[cfg(feature = "postcopy")]
     fn postcopy_end(&self) -> Result<()>;
+    fn set_log_base(&self, log: &VhostUserLog, file: File) -> Result<()>;
 }
 
 /// Services provided to the frontend by the backend without interior mutability.
@@ -144,6 +145,7 @@ pub trait VhostUserBackendReqHandlerMut {
     fn postcopy_listen(&mut self) -> Result<()>;
     #[cfg(feature = "postcopy")]
     fn postcopy_end(&mut self) -> Result<()>;
+    fn set_log_base(&mut self, log: &VhostUserLog, file: File) -> Result<()>;
 }
 
 impl<T: VhostUserBackendReqHandlerMut> VhostUserBackendReqHandler for Mutex<T> {
@@ -282,6 +284,9 @@ impl<T: VhostUserBackendReqHandlerMut> VhostUserBackendReqHandler for Mutex<T> {
     fn postcopy_end(&self) -> Result<()> {
         self.lock().unwrap().postcopy_end()
     }
+    fn set_log_base(&self, log: &VhostUserLog, file: File) -> Result<()> {
+        self.lock().unwrap().set_log_base(log, file)
+    }
 }
 
 /// Server to handle service requests from frontends from the frontend communication channel.
@@ -649,6 +654,18 @@ impl<S: VhostUserBackendReqHandler> BackendReqHandler<S> {
                 let res = self.backend.postcopy_end();
                 self.send_ack_message(&hdr, res)?;
             }
+            // Sets logging shared memory space.
+            // When the back-end has `VHOST_USER_PROTOCOL_F_LOG_SHMFD` protocol feature, the log
+            // memory `fd` is provided in the ancillary data of `VHOST_USER_SET_LOG_BASE` message,
+            // the size and offset of shared memory area provided in the message.
+            // See https://qemu-project.gitlab.io/qemu/interop/vhost-user.html#migration.
+            Ok(FrontendReq::SET_LOG_BASE) => {
+                self.check_proto_feature(VhostUserProtocolFeatures::LOG_SHMFD)?;
+                let file = take_single_file(files).ok_or(Error::IncorrectFds)?;
+                let msg = self.extract_request_body::<VhostUserLog>(&hdr, size, &buf)?;
+                self.backend.set_log_base(&msg, file)?;
+                self.send_reply_message(&hdr, &msg)?;
+            }
             _ => {
                 return Err(Error::InvalidMessage);
             }

vhost/src/vhost_user/dummy_backend.rs

@@ -326,4 +326,7 @@ impl VhostUserBackendReqHandlerMut for DummyBackendReqHandler {
     fn postcopy_end(&mut self) -> Result<()> {
         Ok(())
     }
+    fn set_log_base(&mut self, _log: &VhostUserLog, _file: File) -> Result<()> {
+        Err(Error::InvalidMessage)
+    }
 }

vhost/src/vhost_user/message.rs

@@ -394,6 +394,8 @@ bitflags! {
     #[derive(Copy, Clone, Debug, Eq, PartialEq)]
     /// Transport specific flags in VirtIO feature set defined by vhost-user.
     pub struct VhostUserVirtioFeatures: u64 {
+        /// Log dirtied shared memory pages.
+        const LOG_ALL = 0x400_0000;
         /// Feature flag for the protocol feature.
         const PROTOCOL_FEATURES = 0x4000_0000;
     }