From 82d7b9f094cd80d7cb3931a3a108f37a11f0fc17 Mon Sep 17 00:00:00 2001
From: Dylan Reid <dgreid@chromium.org>
Date: Tue, 2 Jun 2020 18:33:33 -0700
Subject: [PATCH] vm_memory: Implement cros_async::BackingMemory for
 GuestMemory

Implementing `BackingMemory` signals that `GuestMemory` regions can be
used in uring transactions where the lifetime in which the kernel can
modify the memory is not well defined.

Change-Id: I3541fff4c5dac226062a94483672f570e7adeb18
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2275725
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Commit-Queue: Dylan Reid <dgreid@chromium.org>
Tested-by: Dylan Reid <dgreid@chromium.org>
---
 Cargo.lock                    |  2 +-
 cros_async/Cargo.toml         |  2 +-
 cros_async/src/lib.rs         |  4 ++--
 vm_memory/Cargo.toml          |  1 +
 vm_memory/src/guest_memory.rs | 23 +++++++++++++++++++++++
 5 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 06e2a8e46b..6ee3a19c02 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -106,7 +106,6 @@ dependencies = [
  "pin-utils 0.1.0-alpha.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "sys_util 0.1.0",
  "syscall_defines 0.1.0",
- "vm_memory 0.1.0",
 ]
 
 [[package]]
@@ -809,6 +808,7 @@ dependencies = [
 name = "vm_memory"
 version = "0.1.0"
 dependencies = [
+ "cros_async 0.1.0",
  "data_model 0.1.0",
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "sys_util 0.1.0",
diff --git a/cros_async/Cargo.toml b/cros_async/Cargo.toml
index c8760ee7d3..b7196f315d 100644
--- a/cros_async/Cargo.toml
+++ b/cros_async/Cargo.toml
@@ -11,7 +11,6 @@ paste = "*"
 pin-utils = "0.1.0-alpha.4"
 sys_util = { path = "../sys_util" }
 syscall_defines = { path = "../syscall_defines" }
-vm_memory = { path = "../vm_memory" }
 
 [dependencies.futures]
 version = "*"
@@ -20,3 +19,4 @@ features = ["alloc"]
 
 [dev-dependencies]
 tempfile = { path = "../tempfile" }
+vm_memory = { path = "../vm_memory" }
diff --git a/cros_async/src/lib.rs b/cros_async/src/lib.rs
index 1a4edcd5a7..399fd5f032 100644
--- a/cros_async/src/lib.rs
+++ b/cros_async/src/lib.rs
@@ -68,7 +68,7 @@ mod poll_source;
 mod select;
 mod uring_executor;
 mod uring_futures;
-mod uring_mem;
+pub mod uring_mem;
 mod waker;
 
 pub use executor::Executor;
@@ -77,7 +77,7 @@ pub use poll_or_ring::Error as AsyncError;
 pub use poll_or_ring::{PollOrRing, U64Source};
 pub use select::SelectResult;
 pub use uring_futures::UringSource;
-pub use uring_mem::MemRegion;
+pub use uring_mem::{BackingMemory, MemRegion};
 
 use std::fmt::{self, Display};
 use std::future::Future;
diff --git a/vm_memory/Cargo.toml b/vm_memory/Cargo.toml
index 077eab7c47..bc7336b985 100644
--- a/vm_memory/Cargo.toml
+++ b/vm_memory/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 include = ["src/**/*", "Cargo.toml"]
 
 [dependencies]
+cros_async = { path = "../cros_async" } # provided by ebuild
 data_model = { path = "../data_model" } # provided by ebuild
 libc = "*"
 sys_util = { path = "../sys_util" } # provided by ebuild
diff --git a/vm_memory/src/guest_memory.rs b/vm_memory/src/guest_memory.rs
index 63275c8c03..7a96769353 100644
--- a/vm_memory/src/guest_memory.rs
+++ b/vm_memory/src/guest_memory.rs
@@ -13,6 +13,10 @@ use std::result;
 use std::sync::Arc;
 
 use crate::guest_address::GuestAddress;
+use cros_async::{
+    uring_mem::{self, BorrowedIoVec},
+    BackingMemory,
+};
 use data_model::volatile_memory::*;
 use data_model::DataInit;
 use sys_util::{pagesize, Error as SysError};
@@ -665,6 +669,25 @@ impl GuestMemory {
     }
 }
 
+// It is safe to implement BackingMemory because GuestMemory can be mutated any time already.
+unsafe impl BackingMemory for GuestMemory {
+    fn get_iovec<'s>(
+        &'s self,
+        mem_range: cros_async::MemRegion,
+    ) -> uring_mem::Result<uring_mem::BorrowedIoVec<'s>> {
+        let vs = self
+            .get_slice_at_addr(GuestAddress(mem_range.offset as u64), mem_range.len)
+            .map_err(|_| uring_mem::Error::InvalidOffset(mem_range.offset, mem_range.len))?;
+        // Safe because 'vs' is valid in the backing memory as checked above.
+        unsafe {
+            Ok(BorrowedIoVec::from_raw_parts(
+                vs.as_mut_ptr(),
+                vs.size() as usize,
+            ))
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;