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kvm: add dirty_log_bitmap_size helper

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For the callers of get_dirty_log, they must pass in bitmap large enough
to hold the log. Instead of duplicating that calculation inside the
method and the caller, this change provides a public helper usable by
both to calculate the bitmap's minimum size.

TEST=./build_test
BUG=chromium:800626

Change-Id: I349aa0dd7e78e7f9ea3d35ba0acba8088fd77a4e
Reviewed-on: https://chromium-review.googlesource.com/857909
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
This commit is contained in:
Zach Reizner 2018-01-09 15:19:23 -08:00 committed by chrome-bot
parent 0335dad57e
commit d48d7f10b5
1 changed files with 23 additions and 3 deletions
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26
kvm/src/lib.rs
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@ -56,6 +56,17 @@ unsafe fn set_user_memory_region<F: AsRawFd>(fd: &F,
if ret == 0 { Ok(()) } else { errno_result() }
}
/// Helper function to determine the size in bytes of a dirty log bitmap for the given memory region
/// size.
///
/// # Arguments
///
/// * `size` - Number of bytes in the memory region being queried.
pub fn dirty_log_bitmap_size(size: usize) -> usize {
let page_size = pagesize();
(((size + page_size - 1) / page_size) + 7) / 8
}
/// A wrapper around opening and using `/dev/kvm`.
///
/// Useful for querying extensions and basic values from the KVM backend. A `Kvm` is required to
@ -266,11 +277,10 @@ impl Vm {
/// region `slot` represents. For example, if the size of `slot` is 16 pages, `dirty_log` must
/// be 2 bytes or greater.
pub fn get_dirty_log(&self, slot: u32, dirty_log: &mut [u8]) -> Result<()> {
let page_size = pagesize();
match self.device_memory.get(&slot) {
Some(mmap) => {
// Ensures that there are as many bits in dirty_log as there are pages in the mmap.
if (mmap.size() / page_size) > (dirty_log.len() << 3) {
// Ensures that there are as many bytes in dirty_log as there are pages in the mmap.
if dirty_log_bitmap_size(mmap.size()) > dirty_log.len() {
return Err(Error::new(-EINVAL));
}
let mut dirty_log_kvm = kvm_dirty_log {
@ -828,6 +838,16 @@ impl CpuId {
mod tests {
use super::*;
#[test]
fn dirty_log_size() {
let page_size = pagesize();
assert_eq!(dirty_log_bitmap_size(0), 0);
assert_eq!(dirty_log_bitmap_size(page_size), 1);
assert_eq!(dirty_log_bitmap_size(page_size * 8), 1);
assert_eq!(dirty_log_bitmap_size(page_size * 8 + 1), 2);
assert_eq!(dirty_log_bitmap_size(page_size * 100), 13);
}
#[test]
fn new() {
Kvm::new().unwrap();