Apply same permissions to pmem-region alignments.

https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1979257
created a padding of read-only pages between the end of the pmem region
and padding up to the next multiple of 2MiB.  However, on ARM systems,
kvm_arch_prepare_memory_region does not permit read-only pages on a
write-able memory region.

BUG=b:148706939
TEST=Tested on x86_64 and arm64 board with pmem image < 2MiB
Tested-by: Iliyan Malchev <malchev@google.com>

Change-Id: If06c2e0f74fdcd7db1b7d56e1a8d732d17f352bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2153103
Tested-by: Dylan Reid <dgreid@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Stephen Barber <smbarber@chromium.org>

1 files changed, 5 insertions, 9 deletions

diff --git a/src/linux.rs b/src/linux.rs
index c8eb478..6a50449 100644
--- a/src/linux.rs
+++ b/src/linux.rs
@@ -890,7 +890,7 @@ fn create_pmem_device(
         .open(&disk.path)
         .map_err(|e| Error::Disk(disk.path.to_path_buf(), e))?;
 
-    let (disk_size, arena_size) = {
+    let arena_size = {
         let metadata =
             std::fs::metadata(&disk.path).map_err(|e| Error::Disk(disk.path.to_path_buf(), e))?;
         let disk_len = metadata.len();
@@ -905,12 +905,9 @@ fn create_pmem_device(
         } else {
             0
         };
-        (
-            disk_len,
-            disk_len
-                .checked_add(align_adjust)
-                .ok_or(Error::PmemDeviceImageTooBig)?,
-        )
+        disk_len
+            .checked_add(align_adjust)
+            .ok_or(Error::PmemDeviceImageTooBig)?
     };
 
     let protection = {
@@ -924,11 +921,10 @@ fn create_pmem_device(
     let arena = {
         // Conversion from u64 to usize may fail on 32bit system.
         let arena_size = usize::try_from(arena_size).map_err(|_| Error::PmemDeviceImageTooBig)?;
-        let disk_size = usize::try_from(disk_size).map_err(|_| Error::PmemDeviceImageTooBig)?;
 
         let mut arena = MemoryMappingArena::new(arena_size).map_err(Error::ReservePmemMemory)?;
         arena
-            .add_fd_offset_protection(0, disk_size, &fd, 0, protection)
+            .add_fd_offset_protection(0, arena_size, &fd, 0, protection)
             .map_err(Error::ReservePmemMemory)?;
         arena
     };