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vmm: memory_manager: Avoid MAP_PRIVATE CoW with VFIO for hugepages too
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>
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@ -1299,30 +1299,36 @@ impl MemoryManager {
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host_numa_node: Option<u32>,
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host_numa_node: Option<u32>,
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existing_memory_file: Option<File>,
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existing_memory_file: Option<File>,
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) -> Result<Arc<GuestRegionMmap>, Error> {
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) -> Result<Arc<GuestRegionMmap>, Error> {
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let mut mmap_flags = libc::MAP_NORESERVE;
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// The duplication of mmap_flags ORing here is unfortunate but it also makes
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// the complexity of the handling clear.
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let fo = if let Some(f) = existing_memory_file {
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let fo = if let Some(f) = existing_memory_file {
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// It must be MAP_SHARED as we wouldn't already have an FD
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mmap_flags |= libc::MAP_SHARED;
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Some(FileOffset::new(f, file_offset))
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Some(FileOffset::new(f, file_offset))
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} else if let Some(backing_file) = backing_file {
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} else if let Some(backing_file) = backing_file {
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if shared {
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mmap_flags |= libc::MAP_SHARED;
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} else {
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mmap_flags |= libc::MAP_PRIVATE;
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}
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Some(Self::open_backing_file(backing_file, file_offset, size)?)
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Some(Self::open_backing_file(backing_file, file_offset, size)?)
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} else if shared || hugepages {
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} else if shared || hugepages {
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// For hugepages we must also MAP_SHARED otherwise we will trigger #4805
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// because the MAP_PRIVATE will trigger CoW against the backing file with
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// the VFIO pinning
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mmap_flags |= libc::MAP_SHARED;
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Some(Self::create_anonymous_file(size, hugepages, hugepage_size)?)
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Some(Self::create_anonymous_file(size, hugepages, hugepage_size)?)
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} else {
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} else {
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mmap_flags |= libc::MAP_PRIVATE | libc::MAP_ANONYMOUS;
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None
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None
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};
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};
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let mut mmap_flags = libc::MAP_NORESERVE
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libc::MAP_SHARED
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} else {
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libc::MAP_PRIVATE
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};
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if prefault {
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if prefault {
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mmap_flags |= libc::MAP_POPULATE;
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mmap_flags |= libc::MAP_POPULATE;
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}
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}
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if fo.is_none() {
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mmap_flags |= libc::MAP_ANONYMOUS;
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}
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let region = GuestRegionMmap::new(
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let region = GuestRegionMmap::new(
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MmapRegion::build(fo, size, libc::PROT_READ | libc::PROT_WRITE, mmap_flags)
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MmapRegion::build(fo, size, libc::PROT_READ | libc::PROT_WRITE, mmap_flags)
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.map_err(Error::GuestMemoryRegion)?,
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.map_err(Error::GuestMemoryRegion)?,
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