Re: [PATCH RFT 0/3] mm, drm: ensure .fault() does not have to be followed by .pfn_mkwrite() for write faults
Paolo Bonzini <[email protected]>
| Newsgroups | gmane.comp.emulators.kvm.devel,gmane.linux.kernel,gmane.comp.video.dri.devel,gmane.linux.kernel.mm |
|---|---|
| Message-ID | <CABgObfaCTroScRykMHRk6fLktzG7CT2Prp2f-CCCANfuagv_MQ@mail.gmail.com> |
On Mon, Aug 3, 2026 at 5:18 PM David Hildenbrand (Arm) <[email protected]> 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