On Thu, Nov 13, 2025 at 02:48:44PM +0530, Anshuman Khandual wrote:

On 03/11/25 10:56 AM, Anshuman Khandual wrote:

quoted

This series contains some TTBRx_EL1 related changes, aimed at standardizing
TTBRx_EL1 register field accesses via tools sysreg format and also explains
52 PA specific handling methods via a new macro along with in code comments

This series applies on v6.18-rc4

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

Anshuman Khandual (6):
  arm64/mm: Directly use TTBRx_EL1_ASID_MASK
  arm64/mm: Directly use TTBRx_EL1_CnP
  arm64/mm: Represent TTBR_BADDR_MASK_52 with TTBRx_EL1_BADDR_MASK
  arm64/mm: Ensure correct 48 bit PA gets into TTBRx_EL1
  arm64/mm: Describe 52 PA folding into TTBRx_EL1
  arm64/mm: Describe TTBR1_BADDR_4852_OFFSET

 arch/arm64/include/asm/asm-uaccess.h   |  2 +-
 arch/arm64/include/asm/assembler.h     |  3 ++-
 arch/arm64/include/asm/mmu_context.h   |  2 +-
 arch/arm64/include/asm/pgtable-hwdef.h | 23 ++++++++++++++++++++---
 arch/arm64/include/asm/pgtable.h       |  5 +++--
 arch/arm64/include/asm/uaccess.h       |  6 +++---
 arch/arm64/kernel/entry.S              |  2 +-
 arch/arm64/kernel/mte.c                |  4 ++--
 arch/arm64/mm/context.c                |  8 ++++----
 arch/arm64/mm/mmu.c                    |  2 +-
 10 files changed, 38 insertions(+), 19 deletions(-)

Gentle ping. Beside [PATCH 4/6] (which can be dropped as indicated by Mark)
any concerns regarding reset of these changes here ?

Overall I don;t think this series actually improves anything; it just
shuffles things around, and leaves conversions half-done. I don't think
we must take this as-is.

For patches 1 and 2, the changes would be fine if we were also getting
rid of TTBR_ASID_MASK and TTBR_CNP_BIT, but we don't, apparently because
those are still used by KVM. It feels like those two patches should be
split into a separate series that *only* moves code over to generate
sysreg definitions, also updates KVM, and removes the unused legacy
definitions.

For patch 3, I think the change makes the code harder to read, and
harder to understand, because there's no context to explain why we're
masking out a single bit. I don't think this is actually an improvement.
See below for related notes for patch 5.

For patch 4, as above, I think the patch can be dropped.

For patch 5, this could be OK, but we should define
TTBR_BADDR_52_PA_PIVOT as (51 - 5) and avoid the magic number entirely.
IMO it'd be nicer to just extract and re-insert the bits; I think our
current logic is unnecessarily micro-optimized so that this can be
implemented with a shifted-OR + AND, whereas I think we could burn a
temporary register and use BFX + BFI + AND, and that would be clearer as
to *which* bits we're trying to move.

For patch 6, I guess this is fine; I don't have a strong feeling either
way.

Mark.