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vmm: memory_manager: Avoid MAP_PRIVATE CoW with VFIO for hugepages too

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We can't use MAP_ANONYMOUS and still have huge pages so MAP_SHARED is
effectively required when using huge pages.

Unfortunately it is not as simple as always forcing MAP_SHARED if
hugepages is on as this might be inappropriate in the backing file case
hence why there is additional complexity of assigning to mmap_flags on
each case and the MAP_SHARED is only turned on for the anonymous file
huge page case as well as anonymous shared file case.

See: #4805

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2022-10-30 10:32:52 +00:00
parent df7c728399
commit 99d9a3d299
1 changed files with 16 additions and 10 deletions
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26
vmm/src/memory_manager.rs
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@ -1299,30 +1299,36 @@ impl MemoryManager {
host_numa_node: Option<u32>,
existing_memory_file: Option<File>,
) -> Result<Arc<GuestRegionMmap>, Error> {
let mut mmap_flags = libc::MAP_NORESERVE;
// The duplication of mmap_flags ORing here is unfortunate but it also makes
// the complexity of the handling clear.
let fo = if let Some(f) = existing_memory_file {
// It must be MAP_SHARED as we wouldn't already have an FD
mmap_flags |= libc::MAP_SHARED;
Some(FileOffset::new(f, file_offset))
} else if let Some(backing_file) = backing_file {
if shared {
mmap_flags |= libc::MAP_SHARED;
} else {
mmap_flags |= libc::MAP_PRIVATE;
}
Some(Self::open_backing_file(backing_file, file_offset, size)?)
} else if shared || hugepages {
// For hugepages we must also MAP_SHARED otherwise we will trigger #4805
// because the MAP_PRIVATE will trigger CoW against the backing file with
// the VFIO pinning
mmap_flags |= libc::MAP_SHARED;
Some(Self::create_anonymous_file(size, hugepages, hugepage_size)?)
} else {
mmap_flags |= libc::MAP_PRIVATE | libc::MAP_ANONYMOUS;
None
};
let mut mmap_flags = libc::MAP_NORESERVE
| if shared {
libc::MAP_SHARED
} else {
libc::MAP_PRIVATE
};
if prefault {
mmap_flags |= libc::MAP_POPULATE;
}
if fo.is_none() {
mmap_flags |= libc::MAP_ANONYMOUS;
}
let region = GuestRegionMmap::new(
MmapRegion::build(fo, size, libc::PROT_READ | libc::PROT_WRITE, mmap_flags)
.map_err(Error::GuestMemoryRegion)?,