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Previously, guest-memfd allocations followed local NUMA node id in absence of process mempolicy, resulting in arbitrary memory allocation. Moreover, mbind() couldn't be used by the VMM as guest memory wasn't mapped into userspace when allocation occurred. Enable NUMA policy support by implementing vm_ops for guest-memfd mmap operation. This allows the VMM to use mmap()+mbind() to set the desired NUMA policy for a range of memory, and provides fine-grained control over guest memory allocation across NUMA nodes. Note, using mmap()+mbind() works even for PRIVATE memory, as mbind() doesn't require the memory to be faulted in. However, get_mempolicy() and other paths that require the userspace page tables to be populated may return incorrect information for PRIVATE memory (though under the hood, KVM+guest_memfd will still behave correctly). Store the policy in the inode structure, gmem_inode, as a shared memory policy, so that the policy is a property of the physical memory itself, i.e. not bound to the VMA. In guest_memfd, KVM is the primary MMU and any VMAs are secondary, i.e. using mbind() on a VMA to set policy is a means to an end, e.g. to avoid having to add a file-based equivalent to mbind(). Similarly, retrieve the policy via mpol_shared_policy_lookup(), not get_vma_policy(), even when allocating to fault in memory for userspace mappings, so that the policy stored in gmem_inode is always the source of true. Apply policy changes only to future allocations, i.e. do not migrate existing memory in the guest_memfd instance. This matches mbind(2)'s default behavior, which affects only new allocations unless overridden with MPOL_MF_MOVE/MPOL_MF_MOVE_ALL flags (which are not supported by guest_memfd as guest_memfd memory is unmovable). Suggested-by: David Hildenbrand <david@redhat.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Shivank Garg <shivankg@amd.com> Tested-by: Ashish Kalra <ashish.kalra@amd.com> Link: https://lore.kernel.org/all/e9d43abc-bcdb-4f9f-9ad7-5644f714de19@amd.com [sean: fold in fixup (see Link above), massage changelog] Link: https://lore.kernel.org/r/20251016172853.52451-6-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.