[PATCH V2 0/8] arm64/mm: Drop PXD_TABLE_BIT

[Anshuman Khandual]

On 2/28/25 21:02, Ryan Roberts wrote:
> On 21/02/2025 04:42, Anshuman Khandual wrote:
>> Remove the PXX_TABLE_BIT definitions and instead rely on PXX_TYPE_MASK,
>> PXX_TYPE_SECT and PXX_TYPE_TABLE. The latter versions are more abstract
>> and also include the PTE_VALID bit.
>>
>> This abstraction is valuable for the impending D128 page table support,
>> which doesn't have a single page table bit to determine table vs block.
>> Instead it has the skip level (SKL) field, where it will consider 0 to
>> mean table and any other value to mean a block entry. So PXX_TABLE_BIT
>> therefore doesn't fit into the D128 model well, but the type fields do.
> 
> All the patches look logically correct to me and I agree with the intention of
> removing PXX_TABLE_BIT. But personally I'd prefer to see a single patch that
> just does everything that's required to remove PXX_TABLE_BIT. And then a second
> patch for the pud_bad() fix/improvement (currently patch 6) which is orthogonal
> to the removal of PXX_TABLE_BIT.
> 
> That would make it much easier to review IMHO, and would also allow for writing
> a single commit log which provides the justification for the change. I find the
> current set of 7 commit logs to not be hugely helpful.

Dropping PXX_TABLE_BIT from individual functional components which stand on their
own progressively leads to its complete removal from the tree. Even though goal
is PXX_TABLE_BIT mask's complete removal, each patch here could be justified on
its own improving consistent reasoning around various section mapping creation
and identification while keeping the functionality unchanged and also improving
code readability as well.

> 
> But I wrote the original patches and wrote them as I'm suggesting, so I would
> say that :)

I can understand :) Although it also follows and expands on the previous attempt
in removing this mask that formed a patch series instead.

https://lore.kernel.org/all/20241005123824.1366397-1-anshuman.khandual@arm.com/

TBH this is not a big deal. I can merge all but last one into a single patch as
you have suggested if that's a general consensus. Although I would prefer the
current logically progressive series based approach but that's just me.

> 
> I'm guessing I shouldn't provide a Reviewed-By here, given I wrote the code
> originally...
> 
> Thanks,
> Ryan
> 
> 
>>
>> This series applies on v6.14-rc3.
>>
>> Changes in V2:
>>
>> - Changed pmd_mkhuge() and pud_mkhuge() implementation
>> - Changed pud_bad() implementation with an additional patch
>>
>> Changes in V1:
>>
>> https://lore.kernel.org/all/20241005123824.1366397-1-anshuman.khandual@arm.com/
>>
>> Cc: Marc Zyngier <maz at kernel.org>
>> Cc: Oliver Upton <oliver.upton at linux.dev>
>> Cc: James Morse <james.morse at arm.com>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: Will Deacon <will at kernel.org>
>> Cc: Ard Biesheuvel <ardb at kernel.org>
>> Cc: Ryan Roberts <ryan.roberts at arm.com>
>> Cc: Mark Rutland <mark.rutland at arm.com>
>> Cc: kvmarm at lists.linux.dev
>> Cc: linux-arm-kernel at lists.infradead.org
>> Cc: linux-kernel at vger.kernel.org
>>
>> Anshuman Khandual (6):
>>   KVM: arm64: ptdump: Test PMD_TYPE_MASK for block mapping
>>   arm64/ptdump: Test PMD_TYPE_MASK for block mapping
>>   arm64/mm: Clear PXX_TYPE_MASK in mk_[pmd|pud]_sect_prot()
>>   arm64/mm: Clear PXX_TYPE_MASK and set PXD_TYPE_SECT in [pmd|pud]_mkhuge()
>>   arm64/mm: Check PXD_TYPE_TABLE in [p4d|pgd]_bad()
>>   arm64/mm: Drop PXD_TABLE_BIT
>>
>> Ryan Roberts (2):
>>   arm64/mm: Check PUD_TYPE_TABLE in pud_bad()
>>   arm64/mm: Check pmd_table() in pmd_trans_huge()
>>
>>  arch/arm64/include/asm/pgtable-hwdef.h |  5 --
>>  arch/arm64/include/asm/pgtable.h       | 65 ++++++++++++++++++--------
>>  arch/arm64/kvm/ptdump.c                |  4 +-
>>  arch/arm64/mm/ptdump.c                 |  4 +-
>>  4 files changed, 50 insertions(+), 28 deletions(-)
>>
>