[linux-nvidia-6.8] arm64: contpte: fix set_access_flags() no-op check for SMMU/ATS faults

[nvmochs]

contpte_ptep_set_access_flags() compared the gathered ptep_get() value against the requested entry to detect no-ops. ptep_get() ORs AF/dirty from all sub-PTEs in the CONT block, so a dirty sibling can make the target appear already-dirty. When the gathered value matches entry, the function returns 0 even though the target sub-PTE still has PTE_RDONLY set in hardware.

For a CPU with FEAT_HAFDBS this gathered view is fine, since hardware may set AF/dirty on any sub-PTE and CPU TLB behavior is effectively gathered across the CONT range. But page-table walkers that evaluate each descriptor individually (e.g. a CPU without DBM support, or an SMMU without HTTU, or with HA/HD disabled in CD.TCR) can keep faulting on the unchanged target sub-PTE, causing an infinite fault loop.

Gathering can therefore cause false no-ops when only a sibling has been updated:

• write faults: target still has PTE_RDONLY (needs PTE_RDONLY cleared)
• read faults: target still lacks PTE_AF

Fix by checking each sub-PTE against the requested AF/dirty/write state (the same bits consumed by __ptep_set_access_flags()), using raw per-PTE values rather than the gathered ptep_get() view, before returning no-op. Keep using the raw target PTE for the write-bit unfold decision.

Per Arm ARM (DDI 0487) D8.7.1 ("The Contiguous bit"), any sub-PTE in a CONT range may become the effective cached translation and software must maintain consistent attributes across the range.

Fixes: 4602e57 ("arm64/mm: wire up PTE_CONT for user mappings")
Cc: Ryan Roberts ryan.roberts@arm.com
Cc: Catalin Marinas catalin.marinas@arm.com
Cc: Will Deacon will@kernel.org
Cc: Jason Gunthorpe jgg@nvidia.com
Cc: John Hubbard jhubbard@nvidia.com
Cc: Zi Yan ziy@nvidia.com
Cc: Breno Leitao leitao@debian.org
Cc: stable@vger.kernel.org
Reviewed-by: Alistair Popple apopple@nvidia.com
Reviewed-by: James Houghton jthoughton@google.com
Reviewed-by: Ryan Roberts ryan.roberts@arm.com
Reviewed-by: Catalin Marinas catalin.marinas@arm.com
Tested-by: Breno Leitao leitao@debian.org

Acked-by: Balbir Singh balbirs@nvidia.com

(backported from commit 97c5550) [mochs: minor context adjustment due to lack of contpte_clear_young_dirty_ptes()]

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This v7.0 fix patch is needed to resolve a hang in pageable D2H copy. See nvb#5931592.

The fix was tested using the cuda_d2h_pageable.py script attached to the bug.

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LP: https://bugs.launchpad.net/ubuntu/+source/linux-nvidia/+bug/2143602

[clsotog]

Acked-by: Carol L Soto csoto@nvidia.com

[jamieNguyenNVIDIA]

Acked-by: Jamie Nguyen <jamien@nvidia.com>

[nvmochs]

PR submitted to Canonical.