On Wed, May 12, 2021 at 09:59:33AM +0200, Ard Biesheuvel wrote:

On Wed, 12 May 2021 at 09:34, Mike Rapoport [off-list ref] wrote:

quoted

On Wed, May 12, 2021 at 09:00:02AM +0200, Ard Biesheuvel wrote:

quoted

On Tue, 11 May 2021 at 12:05, Mike Rapoport [off-list ref] wrote:

quoted

From: Mike Rapoport <redacted>

Hi,

These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire
pfn_valid_within() to 1.

The idea is to mark NOMAP pages as reserved in the memory map and restore
the intended semantics of pfn_valid() to designate availability of struct
page for a pfn.

With this the core mm will be able to cope with the fact that it cannot use
NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks
will be treated correctly even without the need for pfn_valid_within.

The patches are boot tested on qemu-system-aarch64.

Did you use EFI boot when testing this? The memory map is much more
fragmented in that case, so this would be a good data point.

Right, something like this:

Yes, although it is not always that bad.

quoted

[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x0000000040000000-0x00000000ffffbfff]
[    0.000000]   node   0: [mem 0x00000000ffffc000-0x00000000ffffffff]

This is allocated below 4 GB by the firmware, for reasons that are
only valid on x86 (where some of the early boot chain is IA32 only)

quoted

[    0.000000]   node   0: [mem 0x0000000100000000-0x00000004386fffff]
[    0.000000]   node   0: [mem 0x0000000438700000-0x000000043899ffff]
[    0.000000]   node   0: [mem 0x00000004389a0000-0x00000004389bffff]
[    0.000000]   node   0: [mem 0x00000004389c0000-0x0000000438b5ffff]
[    0.000000]   node   0: [mem 0x0000000438b60000-0x000000043be3ffff]
[    0.000000]   node   0: [mem 0x000000043be40000-0x000000043becffff]
[    0.000000]   node   0: [mem 0x000000043bed0000-0x000000043bedffff]
[    0.000000]   node   0: [mem 0x000000043bee0000-0x000000043bffffff]
[    0.000000]   node   0: [mem 0x000000043c000000-0x000000043fffffff]

This is a pity really, because I don't see a fundamental reason for those
tiny holes all over the place.

There is a config option in the firmware build that allows these
regions to be preallocated using larger windows, which greatly reduces
the fragmentation.

quoted

I know that EFI/ACPI mandates "IO style" memory access for those regions,
but I fail to get why...

Not sure what you mean by 'IO style memory access'.

 
Well, my understanding is that the memory reserved by the firmware cannot
be mapped in the linear map because it might require different caching
modes (e.g like IO) and arm64 cannot tolerate aliased mappings with
different caching.
But what evades me is *why* these areas cannot be accessed as normal RAM.
 

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I beleive it would be best to route these via mmotm tree.

v4:
* rebase on v5.13-rc1

v3: Link: https://lore.kernel.org/lkml/20210422061902.21614-1-rppt@kernel.org (local)
* Fix minor issues found by Anshuman
* Freshen up the declaration of pfn_valid() to make it consistent with
  pfn_is_map_memory()
* Add more Acked-by and Reviewed-by tags, thanks Anshuman and David

v2: Link: https://lore.kernel.org/lkml/20210421065108.1987-1-rppt@kernel.org (local)
* Add check for PFN overflow in pfn_is_map_memory()
* Add Acked-by and Reviewed-by tags, thanks David.

v1: Link: https://lore.kernel.org/lkml/20210420090925.7457-1-rppt@kernel.org (local)
* Add comment about the semantics of pfn_valid() as Anshuman suggested
* Extend comments about MEMBLOCK_NOMAP, per Anshuman
* Use pfn_is_map_memory() name for the exported wrapper for
  memblock_is_map_memory(). It is still local to arch/arm64 in the end
  because of header dependency issues.

rfc: Link: https://lore.kernel.org/lkml/20210407172607.8812-1-rppt@kernel.org (local)

Mike Rapoport (4):
  include/linux/mmzone.h: add documentation for pfn_valid()
  memblock: update initialization of reserved pages
  arm64: decouple check whether pfn is in linear map from pfn_valid()
  arm64: drop pfn_valid_within() and simplify pfn_valid()

 arch/arm64/Kconfig              |  3 ---
 arch/arm64/include/asm/memory.h |  2 +-
 arch/arm64/include/asm/page.h   |  3 ++-
 arch/arm64/kvm/mmu.c            |  2 +-
 arch/arm64/mm/init.c            | 14 +++++++++++++-
 arch/arm64/mm/ioremap.c         |  4 ++--
 arch/arm64/mm/mmu.c             |  2 +-
 include/linux/memblock.h        |  4 +++-
 include/linux/mmzone.h          | 11 +++++++++++
 mm/memblock.c                   | 28 ++++++++++++++++++++++++++--
 10 files changed, 60 insertions(+), 13 deletions(-)


base-commit: 6efb943b8616ec53a5e444193dccf1af9ad627b5
--
2.28.0

--
Sincerely yours,
Mike.

-- 
Sincerely yours,
Mike.