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vmm: memory_manager: Only file back memory when required

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If we do not need an anonymous file backing the memory then do not
create one.

As a side effect this addresses an issue with CoW (mmap with MAP_PRIVATE
but no MAP_ANONYMOUS) when the memory is pinned for VFIO.

Fixes: #4805

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Rob Bradford 2022-10-30 10:27:56 +00:00
parent 1e5a4e8d77
commit df7c728399
1 changed files with 7 additions and 1 deletions
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8
vmm/src/memory_manager.rs
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@ -1303,8 +1303,10 @@ impl MemoryManager {
Some(FileOffset::new(f, file_offset))
} else if let Some(backing_file) = backing_file {
Some(Self::open_backing_file(backing_file, file_offset, size)?)
} else {
} else if shared || hugepages {
Some(Self::create_anonymous_file(size, hugepages, hugepage_size)?)
} else {
None
};
let mut mmap_flags = libc::MAP_NORESERVE
@ -1317,6 +1319,10 @@ impl MemoryManager {
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)?,