From: Paolo Bonzini <pbonzini@redhat.com>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Boris Brezillon <boris.brezillon@collabora.com>,
Thomas Zimmermann <tzimmermann@suse.de>,
Michal Hocko <mhocko@suse.com>, Sergio Lopez <slp@redhat.com>,
Christian Koenig <christian.koenig@amd.com>,
Huang Rui <ray.huang@amd.com>,
bcm-kernel-feedback-list@broadcom.com,
dri-devel@lists.freedesktop.org, linux-mm@kvack.org
Subject: Re: [PATCH RFT 0/3] mm, drm: ensure .fault() does not have to be followed by .pfn_mkwrite() for write faults
Date: Tue, 4 Aug 2026 09:50:21 +0200 [thread overview]
Message-ID: <CABgObfaCTroScRykMHRk6fLktzG7CT2Prp2f-CCCANfuagv_MQ@mail.gmail.com> (raw)
In-Reply-To: <f556ae97-efaf-4e7e-b4f0-0f90087c8555@kernel.org>
On Mon, Aug 3, 2026 at 5:18 PM David Hildenbrand (Arm) <david@kernel.org> wrote:
> >>> Handling this in fixup_user_fault() is problematic: the information
> >>> about the presence of *_mkwrite is only recorded in vma->vm_page_prot,
> >>> which is an opaque pgprot_t, therefore only follow_pfnmap_start()
> >>> knows how to retrieve it.
> >>
> >> How is mprotect() supposed to work in that case?
> >
> I was wondering about the following:
>
> mprotect(PROT_READ)
>
> followed by
>
> mprotect(PROT_READ | PROT_WRITE)
>
> You'd similarly end up without the writable bit in the PTE, and apparently there is not really a way
> to recover from this.
Why not? mprotect_fixup() calls vma_set_page_prot(), the PTE as you
say lacks the writable bit (unless pte_dirty(pte)), and then the next
fault calls .pfn_mkwrite().
Paolo
next prev parent reply other threads:[~2026-08-04 7:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-31 16:43 Paolo Bonzini
2026-07-31 16:43 ` [PATCH RFT 1/3] mm: export variants of vmf_insert_pfn* for use with pfn_mkwrite() Paolo Bonzini
2026-08-03 12:16 ` David Hildenbrand (Arm)
2026-08-04 13:52 ` Christoph Hellwig
2026-08-04 14:35 ` Paolo Bonzini
2026-07-31 16:43 ` [PATCH RFT 2/3] drm/shmem_helper: use vmf_insert_pfn_mkwrite() Paolo Bonzini
2026-08-03 9:55 ` Boris Brezillon
2026-07-31 16:43 ` [PATCH RFT 3/3] drm/ttm, drm/vmwgfx: directly create writable PTEs when mkwrite is in use Paolo Bonzini
2026-08-05 12:58 ` Christian König
2026-08-05 14:48 ` Paolo Bonzini
2026-08-03 7:30 ` [PATCH RFT 0/3] mm, drm: ensure .fault() does not have to be followed by .pfn_mkwrite() for write faults Sergio Lopez Pascual
2026-08-03 11:54 ` David Hildenbrand (Arm)
2026-08-03 14:19 ` Paolo Bonzini
2026-08-03 15:18 ` David Hildenbrand (Arm)
2026-08-04 7:50 ` Paolo Bonzini [this message]
2026-08-04 12:19 ` David Hildenbrand (Arm)
2026-08-03 16:52 ` Paolo Bonzini
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