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,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
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>,
Vlastimil Babka <vbabka@kernel.org>, Jann Horn <jannh@google.com>,
Pedro Falcato <pfalcato@suse.de>
Subject: Re: [PATCH v3 4/9] mm: keep writable entries writable on protection changes
Date: Fri, 13 Nov 2026 19:56:37 +0100 [thread overview]
Message-ID: <603cd8e0-c2c5-4c1e-85c4-d0a5ceda8d4c@kernel.org> (raw)
In-Reply-To: <20261112142039.907090-6-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.
> In shared mappings, it relies on the dirty bit for this, as a clean
> entry might still need a write fault to notify the FS.
>
> However, this misses clean entries that were already writable. For
> example, a uffd-wp unprotect makes shmem PTEs read-only if they were
> mapped by a read fault before uffd-wp was registered, so the next write
> to each of them faults.
See my other reply, adding such optimizations without any motivation why we
should even care is not really what we want.
Drop it from your series and keep the MM changes to a bare minimum please.
Or is there a real dependency for your work?
--
Cheers,
David
next prev parent reply other threads:[~2026-11-13 18:56 UTC|newest]
Thread overview: 14+ 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
2026-11-12 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)
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) [this message]
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)
2026-11-12 14:20 ` [PATCH v3 6/9] mm/mmu_notifier: add MMU_NOTIFIER_RANGE_PERM_UPGRADE Carlos López
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)
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