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Clarify the lifetime of the return value of rte_mem_virt2iova #60

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Clarify the lifetime of the return value of rte_mem_virt2iova #60

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Commits on Mar 20, 2023

  1. Clarify the lifetime of the return value of rte_mem_virt2iova 

    The Linux kernel will move memory around (changing physical address while
keeping the virtual address constant) for various uses. These include
compaction, autonuma, defragmentation (for future hugetlb allocations) and
many more.

Because of this, one cannot depend on the physical address of any mapping
to be a constant, unless a specific kernel component has pinned the
physical address in place. VFIO_NOIOMMU is an example of a kernel component
that does this.

Note that "mlock()" does NOT do this. mlock() guarantees that the memory
will not be swapped out (hard page fault) but the kernel is allowed, and will,
move memory around for defragmentation. Just using hugetlbfs is also equally
not sufficient for the same reason.

Signed-off-by: Arjan van de Ven <[email protected]>
    @fenrus75
    fenrus75 committed Mar 20, 2023
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