arm64/mm: new ptep layer to manage contig bit

Create a new layer for the in-table PTE manipulation APIs. For now, The
existing API is prefixed with double underscore to become the arch-private
API and the public API is just a simple wrapper that calls the private
API.

The public API implementation will subsequently be used to transparently
manipulate the contiguous bit where appropriate. But since there are
already some contig-aware users (e.g. hugetlb, kernel mapper), we must
first ensure those users use the private API directly so that the future
contig-bit manipulations in the public API do not interfere with those
existing uses.

The following APIs are treated this way:

- ptep_get
- set_pte
- set_ptes
- pte_clear
- ptep_get_and_clear
- ptep_test_and_clear_young
- ptep_clear_flush_young
- ptep_set_wrprotect
- ptep_set_access_flags

Link: https://lkml.kernel.org/r/20240215103205.2607016-11-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arm64: mm: Add 5 level paging support to fixmap and swapper handling

Add support for using 5 levels of paging in the fixmap, as well as in
the kernel page table handling code which uses fixmaps internally.
This also handles the case where a 5 level build runs on hardware that
only supports 4 levels of paging.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-79-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arm64: mm: omit redundant remap of kernel image

Now that the early kernel mapping is created with all the right
attributes and segment boundaries, there is no longer a need to recreate
it and switch to it. This also means we no longer have to copy the kasan
shadow or some parts of the fixmap from one set of page tables to the
other.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-68-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arm64: mm: Move fixmap region above vmemmap region

Move the fixmap region above the vmemmap region, so that the start of
the vmemmap delineates the end of the region available for vmalloc and
vmap allocations and the randomized placement of the kernel and modules.

In a subsequent patch, we will take advantage of this to reclaim most of
the vmemmap area when running a 52-bit VA capable build with 52-bit
virtual addressing disabled at runtime.

Note that the existing guard region of 256 MiB covers the fixmap and PCI
I/O regions as well, so we can reduce it 8 MiB, which is what we use in
other places too.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20231213084024.2367360-11-ardb@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>

arm64: mm: always map fixmap at page granularity

Today the fixmap code largely maps elements at PAGE_SIZE granularity,
but we special-case the FDT mapping such that it can be mapped with 2M
block mappings when 4K pages are in use. The original rationale for this
was simplicity, but it has some unfortunate side-effects, and
complicates portions of the fixmap code (i.e. is not so simple after
all).

The FDT can be up to 2M in size but is only required to have 8-byte
alignment, and so it may straddle a 2M boundary. Thus when using 2M
block mappings we may map up to 4M of memory surrounding the FDT. This
is unfortunate as most of that memory will be unrelated to the FDT, and
any pages which happen to share a 2M block with the FDT will by mapped
with Normal Write-Back Cacheable attributes, which might not be what we
want elsewhere (e.g. for carve-outs using Non-Cacheable attributes).

The logic to handle mapping the FDT with 2M blocks requires some special
cases in the fixmap code, and ties it to the early page table
configuration by virtue of the SWAPPER_TABLE_SHIFT and
SWAPPER_BLOCK_SIZE constants used to determine the granularity used to
map the FDT.

This patch simplifies the FDT logic and removes the unnecessary mappings
of surrounding pages by always mapping the FDT at page granularity as
with all other fixmap mappings. To do so we statically reserve multiple
PTE tables to cover the fixmap VA range. Since the FDT can be at most
2M, for 4K pages we only need to allocate a single additional PTE table,
and for 16K and 64K pages the existing single PTE table is sufficient.

The PTE table allocation scales with the number of slots reserved in the
fixmap, and so this also makes it easier to add more fixmap entries if
we require those in future.

Our VA layout means that the fixmap will always fall within a single PMD
table (and consequently, within a single PUD/P4D/PGD entry), which we
can verify at compile time with a static_assert(). With that assert a
number of runtime warnings become impossible, and are removed.

I've boot-tested this patch with both 4K and 64K pages.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Link: https://lore.kernel.org/r/20230406152759.4164229-4-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

arm64: mm: move fixmap code to its own file

Over time, arm64's mm/mmu.c has become increasingly large and painful to
navigate. Move the fixmap code to its own file where it can be understood in
isolation.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Link: https://lore.kernel.org/r/20230406152759.4164229-3-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>