Hello, This patchset builds upon a soon-to-be-published WIP patchset that Sean published at https://github.com/sean-jc/linux/tree/x86/kvm_gmem_solo, mentioned at [1]. The tree can be found at: https://github.com/googleprodkernel/linux-cc/tree/gmem-hugetlb-rfc-v1 In this patchset, hugetlb support for KVM's guest_mem (aka gmem) is introduced, allowing VM private memory (for confidential computing) to be backed by hugetlb pages. guest_mem provides userspace with a handle, with which userspace can allocate and deallocate memory for confidential VMs without mapping the memory into userspace. Why use hugetlb instead of introducing a new allocator, like gmem does for 4K and transparent hugepages? + hugetlb provides the following useful functionality, which would otherwise have to be reimplemented: + Allocation of hugetlb pages at boot time, including + Parsing of kernel boot parameters to configure hugetlb + Tracking of usage in hstate + gmem will share the same system-wide pool of hugetlb pages, so users don't have to have separate pools for hugetlb and gmem + Page accounting with subpools + hugetlb pages are tracked in subpools, which gmem uses to reserve pages from the global hstate + Memory charging + hugetlb provides code that charges memory to cgroups + Reporting: hugetlb usage and availability are available at /proc/meminfo, etc The first 11 patches in this patchset is a series of refactoring to decouple hugetlb and hugetlbfs. The central thread binding the refactoring is that some functions (like inode_resv_map(), inode_subpool(), inode_hstate(), etc) rely on a hugetlbfs concept, that the resv_map, subpool, hstate, are in a specific field in a hugetlb inode. Refactoring to parametrize functions by hstate, subpool, resv_map will allow hugetlb to be used by gmem and in other places where these data structures aren't necessarily stored in the same positions in the inode. The refactoring proposed here is just the minimum required to get a proof-of-concept working with gmem. I would like to get opinions on this approach before doing further refactoring. (See TODOs) TODOs: + hugetlb/hugetlbfs refactoring + remove_inode_hugepages() no longer needs to be exposed, it is hugetlbfs specific and used only in inode.c + remove_mapping_hugepages(), remove_inode_single_folio(), hugetlb_unreserve_pages() shouldn't need to take inode as a parameter + Updating inode->i_blocks can be refactored to a separate function and called from hugetlbfs and gmem + alloc_hugetlb_folio_from_subpool() shouldn't need to be parametrized by vma + hugetlb_reserve_pages() should be refactored to be symmetric with hugetlb_unreserve_pages() + It should be parametrized by resv_map + alloc_hugetlb_folio_from_subpool() could perhaps use hugetlb_reserve_pages()? + gmem + Figure out if resv_map should be used by gmem at all + Probably needs more refactoring to decouple resv_map from hugetlb functions Questions for the community: 1. In this patchset, every gmem file backed with hugetlb is given a new subpool. Is that desirable? + In hugetlbfs, a subpool always belongs to a mount, and hugetlbfs has one mount per hugetlb size (2M, 1G, etc) + memfd_create(MFD_HUGETLB) effectively returns a full hugetlbfs file, so it (rightfully) uses the hugetlbfs kernel mounts and their subpools + I gave each file a subpool mostly to speed up implementation and still be able to reserve hugetlb pages from the global hstate based on the gmem file size. + gmem, unlike hugetlbfs, isn't meant to be a full filesystem, so + Should there be multiple mounts, one for each hugetlb size? + Will the mounts be initialized on boot or on first gmem file creation? + Or is one subpool per gmem file fine? 2. Should resv_map be used for gmem at all, since gmem doesn't allow userspace reservations? [1] https://lore.kernel.org/lkml/ZEM5Zq8oo+xnApW9@xxxxxxxxxx/ --- Ackerley Tng (19): mm: hugetlb: Expose get_hstate_idx() mm: hugetlb: Move and expose hugetlbfs_zero_partial_page mm: hugetlb: Expose remove_inode_hugepages mm: hugetlb: Decouple hstate, subpool from inode mm: hugetlb: Allow alloc_hugetlb_folio() to be parametrized by subpool and hstate mm: hugetlb: Provide hugetlb_filemap_add_folio() mm: hugetlb: Refactor vma_*_reservation functions mm: hugetlb: Refactor restore_reserve_on_error mm: hugetlb: Use restore_reserve_on_error directly in filesystems mm: hugetlb: Parametrize alloc_hugetlb_folio_from_subpool() by resv_map mm: hugetlb: Parametrize hugetlb functions by resv_map mm: truncate: Expose preparation steps for truncate_inode_pages_final KVM: guest_mem: Refactor kvm_gmem fd creation to be in layers KVM: guest_mem: Refactor cleanup to separate inode and file cleanup KVM: guest_mem: hugetlb: initialization and cleanup KVM: guest_mem: hugetlb: allocate and truncate from hugetlb KVM: selftests: Add basic selftests for hugetlbfs-backed guest_mem KVM: selftests: Support various types of backing sources for private memory KVM: selftests: Update test for various private memory backing source types fs/hugetlbfs/inode.c | 102 ++-- include/linux/hugetlb.h | 86 ++- include/linux/mm.h | 1 + include/uapi/linux/kvm.h | 25 + mm/hugetlb.c | 324 +++++++----- mm/truncate.c | 24 +- .../testing/selftests/kvm/guest_memfd_test.c | 33 +- .../testing/selftests/kvm/include/test_util.h | 14 + tools/testing/selftests/kvm/lib/test_util.c | 74 +++ .../kvm/x86_64/private_mem_conversions_test.c | 38 +- virt/kvm/guest_mem.c | 488 ++++++++++++++---- 11 files changed, 882 insertions(+), 327 deletions(-) -- 2.41.0.rc0.172.g3f132b7071-goog
