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 | 11 +++ arch/x86/boot/compressed/tdx.c | 27 ++++++ arch/x86/boot/compressed/unaccepted_memory.c | 75 ++++++++++++++++ arch/x86/include/asm/page.h | 5 ++ arch/x86/include/asm/shared/tdx.h | 21 +++++ arch/x86/include/asm/tdx.h | 19 ---- 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 | 6 ++ arch/x86/mm/Makefile | 2 + arch/x86/mm/unaccepted_memory.c | 94 ++++++++++++++++++++ drivers/firmware/efi/Kconfig | 15 ++++ drivers/firmware/efi/efi.c | 1 + drivers/firmware/efi/libstub/x86-stub.c | 88 ++++++++++++++---- include/linux/efi.h | 3 +- include/linux/page-flags.h | 27 ++++++ mm/internal.h | 15 ++++ mm/memblock.c | 8 ++ mm/page_alloc.c | 23 ++++- 25 files changed, 534 insertions(+), 39 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
