On 3/30/23 13:49, Kirill A. Shutemov wrote: > 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. > > TDX-specific code isolated from the core of unaccepted memory support. It > supposed to help to plug-in different implementation of unaccepted memory > such as SEV-SNP. > > -- Fragmentation study -- > > Vlastimil and Mel were concern about effect of unaccepted memory on > fragmentation prevention measures in page allocator. I tried to evaluate > it, but it is tricky. As suggested I tried to run multiple parallel kernel > builds and follow how often kmem:mm_page_alloc_extfrag gets hit. > > I don't like the results. Not because unaccepted memory is slow, but > because the test is way too noisy to produce sensible information. Hmm yeah it can be noisy. Did you try to only count events that have fragmenting=1 and/or MIGRATE_MOVABLE as fallback_migratetype? As those are the really bad events. > So, I run 8 parallel builds of kernel, 16 jobs each in a VM with 16 CPU > and 16G of RAM. I compared unpatched base-line (mm-unstable) with the tree > that has patchset applied. For the later case, all memory above 1G was > considered unaccepted with fake_unaccepted_start=1G. Around 14G of RAM was > accounted as unaccepted after the boot. The test got all memory accepted. > > kmem:mm_page_alloc_extfrag Time elapsed > Base line: > Run 1 837 1803.21s > Run 2 3,845 1785.87s > Run 3 1,704 1883.59s > > Patched: > Run 1 905 1876.02s > Run 2 845 1758.50s > Run 3 1276 1876.13s > > As you can see the numbers are all over the place. > > The good news is that unaccepted memory doesn't make picture notably worse. Yeah that at least somehow confirms no big surprises. I wouldn't expect any with the v9 design of watermarks handling. > I am open to suggestions on how to test it better. > > Also, feel free to play with it yourself. fake_unaccepted_start= doesn't > require any special setup. > > -- > > The tree can be found here: > > https://github.com/intel/tdx.git guest-unaccepted-memory > > The patchset depends on MAX_ORDER changes in MM tree. > > v9: > - Accept memory up to high watermark when kernel runs out of free memory; > - Treat unaccepted memory as unusable in __zone_watermark_unusable_free(); > - Per-zone unaccepted memory accounting; > - All pages on unaccepted list are MAX_ORDER now; > - accept_memory=eager in cmdline to pre-accept memory during the boot; > - Implement fake unaccepted memory; > - Sysfs handle to accept memory manually; > - Drop PageUnaccepted(); > - Rename unaccepted_pages static key to zones_with_unaccepted_pages; > v8: > - Rewrite core-mm support for unaccepted memory (patch 02/14); > - s/UnacceptedPages/Unaccepted/ in meminfo; > - Drop arch/x86/boot/compressed/compiler.h; > - Fix build errors; > - Adjust commit messages and comments; > - Reviewed-bys from Dave and Borislav; > - Rebased to tip/master. > v7: > - Rework meminfo counter to use PageUnaccepted() and move to generic code; > - Fix range_contains_unaccepted_memory() on machines without unaccepted memory; > - Add Reviewed-by from David; > v6: > - Fix load_unaligned_zeropad() on machine with unaccepted memory; > - Clear PageUnaccepted() on merged pages, leaving it only on head; > - Clarify error handling in allocate_e820(); > - Fix build with CONFIG_UNACCEPTED_MEMORY=y, but without TDX; > - Disable kexec at boottime instead of build conflict; > - Rebased to tip/master; > - Spelling fixes; > - Add Reviewed-by from Mike and David; > v5: > - Updates comments and commit messages; > + Explain options for unaccepted memory handling; > - Expose amount of unaccepted memory in /proc/meminfo > - Adjust check in page_expected_state(); > - Fix error code handling in allocate_e820(); > - Centralize __pa()/__va() definitions in the boot stub; > - Avoid includes from the main kernel in the boot stub; > - Use an existing hole in boot_param for unaccepted_memory, instead of adding > to the end of the structure; > - Extract allocate_unaccepted_memory() form allocate_e820(); > - Complain if there's unaccepted memory, but kernel does not support it; > - Fix vmstat counter; > - Split up few preparatory patches; > - Random readability adjustments; > v4: > - PageBuddyUnaccepted() -> PageUnaccepted; > - Use separate page_type, not shared with offline; > - Rework interface between core-mm and arch code; > - Adjust commit messages; > - Ack from Mike; > > Kirill A. Shutemov (14): > x86/boot: Centralize __pa()/__va() definitions > mm: Add support for unaccepted memory > mm/page_alloc: Fake unaccepted memory > mm/page_alloc: Add sysfs handle to accept accept_memory > efi/x86: Get full memory map in allocate_e820() > x86/boot: Add infrastructure required for unaccepted memory support > 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/mm: Avoid load_unaligned_zeropad() stepping into unaccepted memory > x86/tdx: Make _tdx_hypercall() and __tdx_module_call() available in > boot stub > x86/tdx: Refactor try_accept_one() > x86/tdx: Add unaccepted memory support > > Documentation/x86/zero-page.rst | 1 + > arch/x86/Kconfig | 2 + > arch/x86/boot/bitops.h | 40 ++++ > arch/x86/boot/compressed/Makefile | 3 +- > arch/x86/boot/compressed/align.h | 14 ++ > arch/x86/boot/compressed/bitmap.c | 43 ++++ > arch/x86/boot/compressed/bitmap.h | 49 +++++ > arch/x86/boot/compressed/bits.h | 36 ++++ > arch/x86/boot/compressed/efi.h | 1 + > arch/x86/boot/compressed/error.c | 19 ++ > arch/x86/boot/compressed/error.h | 1 + > arch/x86/boot/compressed/find.c | 54 +++++ > arch/x86/boot/compressed/find.h | 79 ++++++++ > arch/x86/boot/compressed/ident_map_64.c | 8 - > arch/x86/boot/compressed/kaslr.c | 35 ++-- > arch/x86/boot/compressed/math.h | 37 ++++ > arch/x86/boot/compressed/mem.c | 122 +++++++++++ > arch/x86/boot/compressed/minmax.h | 61 ++++++ > arch/x86/boot/compressed/misc.c | 6 + > arch/x86/boot/compressed/misc.h | 15 ++ > arch/x86/boot/compressed/pgtable_types.h | 25 +++ > arch/x86/boot/compressed/sev.c | 2 - > arch/x86/boot/compressed/tdx-shared.c | 2 + > arch/x86/boot/compressed/tdx.c | 39 ++++ > arch/x86/coco/tdx/Makefile | 2 +- > arch/x86/coco/tdx/tdx-shared.c | 95 +++++++++ > arch/x86/coco/tdx/tdx.c | 118 +---------- > arch/x86/include/asm/page.h | 3 + > arch/x86/include/asm/shared/tdx.h | 53 +++++ > arch/x86/include/asm/tdx.h | 21 +- > arch/x86/include/asm/unaccepted_memory.h | 16 ++ > arch/x86/include/uapi/asm/bootparam.h | 2 +- > arch/x86/kernel/e820.c | 17 ++ > arch/x86/mm/Makefile | 2 + > arch/x86/mm/unaccepted_memory.c | 107 ++++++++++ > drivers/base/node.c | 7 + > drivers/firmware/efi/Kconfig | 14 ++ > drivers/firmware/efi/efi.c | 1 + > drivers/firmware/efi/libstub/x86-stub.c | 98 +++++++-- > fs/proc/meminfo.c | 5 + > include/linux/efi.h | 3 +- > include/linux/mmzone.h | 8 + > mm/internal.h | 13 ++ > mm/memblock.c | 9 + > mm/mm_init.c | 7 + > mm/page_alloc.c | 246 +++++++++++++++++++++++ > mm/vmstat.c | 3 + > 47 files changed, 1368 insertions(+), 176 deletions(-) > create mode 100644 arch/x86/boot/compressed/align.h > create mode 100644 arch/x86/boot/compressed/bitmap.c > create mode 100644 arch/x86/boot/compressed/bitmap.h > create mode 100644 arch/x86/boot/compressed/bits.h > create mode 100644 arch/x86/boot/compressed/find.c > create mode 100644 arch/x86/boot/compressed/find.h > create mode 100644 arch/x86/boot/compressed/math.h > create mode 100644 arch/x86/boot/compressed/mem.c > create mode 100644 arch/x86/boot/compressed/minmax.h > create mode 100644 arch/x86/boot/compressed/pgtable_types.h > create mode 100644 arch/x86/boot/compressed/tdx-shared.c > create mode 100644 arch/x86/coco/tdx/tdx-shared.c > create mode 100644 arch/x86/include/asm/unaccepted_memory.h > create mode 100644 arch/x86/mm/unaccepted_memory.c >
