From: "David Hildenbrand (Arm)" <david@kernel.org>
To: "Carlos López" <clopez@suse.de>, kvm@vger.kernel.org, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
linux-riscv@lists.infradead.org, seanjc@google.com,
pbonzini@redhat.com, akpm@linux-foundation.org,
peterx@redhat.com, ljs@kernel.org, imbrenda@linux.ibm.com,
borntraeger@linux.ibm.com, frankja@linux.ibm.com,
"Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>
Subject: Re: [PATCH v3 3/9] mm/huge_memory: honor MM_CP_TRY_CHANGE_WRITABLE in change_huge_pud()
Date: Fri, 13 Nov 2026 19:58:08 +0100 [thread overview]
Message-ID: <136002e1-646d-4607-be3f-b6a6a869bbec@kernel.org> (raw)
In-Reply-To: <20261112142039.907090-5-clopez@suse.de>
On 11/12/26 15:20, Carlos López wrote:
> change_protection() applies vma->vm_page_prot, which lacks the write bit
> for CoW and write-notified mappings. MM_CP_TRY_CHANGE_WRITABLE makes
> entries writable again if a write fault would only set the write bit.
>
> However, change_huge_pud() ignores the flag. For example, device DAX
> mappings are write-notified once soft-dirty tracking is armed through
> /proc/pid/clear_refs, and a protection change then leaves dirty PUDs
> read-only, so the next write to each of them faults.
>
> Fix this by adding can_change_pud_writable(), based on
> can_change_pmd_writable(). It omits the NUMA and uffd-wp checks, as
> change_huge_pud() bails out on those changes.
Again, please keep MM changes to a bare minimum for your work.
If this is not required for your work, please drop it.
--
Cheers,
David
next prev parent reply other threads:[~2026-11-13 18:58 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-12 14:20 [PATCH v3 0/9] KVM: don't zap secondary MMU on permission upgrade Carlos López
2026-11-12 14:20 ` [PATCH v3 1/9] mm: fix eager write-bit restore for write-notified shared mappings Carlos López
2026-11-13 20:47 ` Lorenzo Stoakes (ARM)
2026-11-12 14:20 ` [PATCH v3 2/9] riscv: mm: add pud_soft_dirty() Carlos López
2026-11-12 14:20 ` [PATCH v3 3/9] mm/huge_memory: honor MM_CP_TRY_CHANGE_WRITABLE in change_huge_pud() Carlos López
2026-11-13 18:58 ` David Hildenbrand (Arm) [this message]
2026-11-13 20:48 ` Lorenzo Stoakes (ARM)
2026-11-12 14:20 ` [PATCH v3 4/9] mm: keep writable entries writable on protection changes Carlos López
2026-11-13 18:56 ` David Hildenbrand (Arm)
2026-11-12 14:20 ` [PATCH v3 5/9] mm/mprotect: add MM_CP_PERM_UPGRADE Carlos López
2026-11-13 18:51 ` David Hildenbrand (Arm)
2026-11-13 20:37 ` Lorenzo Stoakes (ARM)
2026-11-12 14:20 ` [PATCH v3 6/9] mm/mmu_notifier: add MMU_NOTIFIER_RANGE_PERM_UPGRADE Carlos López
2026-11-13 14:25 ` sashiko-bot
2026-11-12 14:20 ` [PATCH v3 7/9] KVM: pass the mmu_notifier event and flags to kvm_gfn_range Carlos López
2026-11-12 14:20 ` [PATCH v3 8/9] KVM: x86/mmu: don't zap secondary MMU on permission upgrade Carlos López
2026-11-12 14:20 ` [PATCH v3 9/9] KVM: s390: don't unmap the gmap " Carlos López
2026-11-13 19:00 ` [PATCH v3 0/9] KVM: don't zap secondary MMU " David Hildenbrand (Arm)
2026-11-13 20:32 ` Lorenzo Stoakes (ARM)
2026-11-13 20:59 ` Lorenzo Stoakes (ARM)
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