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    Subject[PATCHv2 0/7] Implement support for unaccepted memory
    Date
    UEFI Specification version 2.9 introduces the concept of memory
    acceptance: Some Virtual Machine platforms, such as Intel TDX or AMD
    SEV-SNP, requiring memory to be accepted before it can be used by the
    guest. Accepting happens via a protocol specific for the Virtual
    Machine platform.

    Accepting memory is costly and it makes VMM allocate memory for the
    accepted guest physical address range. It's better to postpone memory
    acceptance until memory is needed. It lowers boot time and reduces
    memory overhead.

    The kernel needs to know what memory has been accepted. Firmware
    communicates this information via memory map: a new memory type --
    EFI_UNACCEPTED_MEMORY -- indicates such memory.

    Range-based tracking works fine for firmware, but it gets bulky for
    the kernel: e820 has to be modified on every page acceptance. It leads
    to table fragmentation, but there's a limited number of entries in the
    e820 table

    Another option is to mark such memory as usable in e820 and track if the
    range has been accepted in a bitmap. One bit in the bitmap represents
    2MiB in the address space: one 4k page is enough to track 64GiB or
    physical address space.

    In the worst-case scenario -- a huge hole in the middle of the
    address space -- It needs 256MiB to handle 4PiB of the address
    space.

    Any unaccepted memory that is not aligned to 2M gets accepted upfront.

    The approach lowers boot time substantially. Boot to shell is ~2.5x
    faster for 4G TDX VM and ~4x faster for 64G.

    Patches 1-6/7 are generic and don't have any dependencies on TDX. They
    should serve AMD SEV needs as well. TDX-specific code isolated in the
    last patch. This patch requires the core TDX patchset which is currently
    under review.

    Kirill A. Shutemov (7):
    mm: Add support for unaccepted memory
    efi/x86: Get full memory map in allocate_e820()
    efi/x86: Implement support for unaccepted memory
    x86/boot/compressed: Handle unaccepted memory
    x86/mm: Reserve unaccepted memory bitmap
    x86/mm: Provide helpers for unaccepted memory
    x86/tdx: Unaccepted memory support

    Documentation/x86/zero-page.rst | 1 +
    arch/x86/Kconfig | 1 +
    arch/x86/boot/compressed/Makefile | 1 +
    arch/x86/boot/compressed/bitmap.c | 86 ++++++++++++++++++
    arch/x86/boot/compressed/kaslr.c | 14 ++-
    arch/x86/boot/compressed/misc.c | 9 ++
    arch/x86/boot/compressed/tdx.c | 67 ++++++++++++++
    arch/x86/boot/compressed/unaccepted_memory.c | 64 +++++++++++++
    arch/x86/include/asm/page.h | 5 ++
    arch/x86/include/asm/tdx.h | 2 +
    arch/x86/include/asm/unaccepted_memory.h | 17 ++++
    arch/x86/include/uapi/asm/bootparam.h | 3 +-
    arch/x86/kernel/e820.c | 10 +++
    arch/x86/kernel/tdx.c | 7 ++
    arch/x86/mm/Makefile | 2 +
    arch/x86/mm/unaccepted_memory.c | 94 ++++++++++++++++++++
    drivers/firmware/efi/Kconfig | 14 +++
    drivers/firmware/efi/efi.c | 1 +
    drivers/firmware/efi/libstub/x86-stub.c | 86 ++++++++++++++----
    include/linux/efi.h | 3 +-
    include/linux/page-flags.h | 4 +
    mm/internal.h | 15 ++++
    mm/memblock.c | 1 +
    mm/page_alloc.c | 21 ++++-
    24 files changed, 508 insertions(+), 20 deletions(-)
    create mode 100644 arch/x86/boot/compressed/bitmap.c
    create mode 100644 arch/x86/boot/compressed/unaccepted_memory.c
    create mode 100644 arch/x86/include/asm/unaccepted_memory.h
    create mode 100644 arch/x86/mm/unaccepted_memory.c

    --
    2.34.1

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