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[2003:cb:c738:3100:8133:26cf:7877:94aa]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e9e6249csm178402255e9.38.2025.01.14.08.15.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jan 2025 08:15:57 -0800 (PST) Message-ID: <17d32dc8-39c1-4aa4-ab8c-873c78097fde@redhat.com> Date: Tue, 14 Jan 2025 17:15:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 13/26] mm/memory: Add vmf_insert_page_mkwrite() To: Alistair Popple , akpm@linux-foundation.org, dan.j.williams@intel.com, linux-mm@kvack.org Cc: alison.schofield@intel.com, lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev References: From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250114_081604_328762_B8551937 X-CRM114-Status: GOOD ( 28.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10.01.25 07:00, Alistair Popple wrote: > Currently to map a DAX page the DAX driver calls vmf_insert_pfn. This > creates a special devmap PTE entry for the pfn but does not take a > reference on the underlying struct page for the mapping. This is > because DAX page refcounts are treated specially, as indicated by the > presence of a devmap entry. > > To allow DAX page refcounts to be managed the same as normal page > refcounts introduce vmf_insert_page_mkwrite(). This will take a > reference on the underlying page much the same as vmf_insert_page, > except it also permits upgrading an existing mapping to be writable if > requested/possible. > > Signed-off-by: Alistair Popple > > --- > > Updates from v2: > > - Rename function to make not DAX specific > > - Split the insert_page_into_pte_locked() change into a separate > patch. > > Updates from v1: > > - Re-arrange code in insert_page_into_pte_locked() based on comments > from Jan Kara. > > - Call mkdrity/mkyoung for the mkwrite case, also suggested by Jan. > --- > include/linux/mm.h | 2 ++ > mm/memory.c | 36 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 38 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index e790298..f267b06 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3620,6 +3620,8 @@ int vm_map_pages(struct vm_area_struct *vma, struct page **pages, > unsigned long num); > int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages, > unsigned long num); > +vm_fault_t vmf_insert_page_mkwrite(struct vm_fault *vmf, struct page *page, > + bool write); > vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn); > vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > diff --git a/mm/memory.c b/mm/memory.c > index 8531acb..c60b819 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2624,6 +2624,42 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma, > return VM_FAULT_NOPAGE; > } > > +vm_fault_t vmf_insert_page_mkwrite(struct vm_fault *vmf, struct page *page, > + bool write) > +{ > + struct vm_area_struct *vma = vmf->vma; > + pgprot_t pgprot = vma->vm_page_prot; > + unsigned long pfn = page_to_pfn(page); > + unsigned long addr = vmf->address; > + int err; > + > + if (addr < vma->vm_start || addr >= vma->vm_end) > + return VM_FAULT_SIGBUS; > + > + track_pfn_insert(vma, &pgprot, pfn_to_pfn_t(pfn)); I think I raised this before: why is this track_pfn_insert() in here? It only ever does something to VM_PFNMAP mappings, and that cannot possibly be the case here (nothing in VM_PFNMAP is refcounted, ever)? > + > + if (!pfn_modify_allowed(pfn, pgprot)) > + return VM_FAULT_SIGBUS; Why is that required? Why are we messing so much with PFNs? :) Note that x86 does in there /* If it's real memory always allow */ if (pfn_valid(pfn)) return true; See below, when would we ever have a "struct page *" but !pfn_valid() ? > + > + /* > + * We refcount the page normally so make sure pfn_valid is true. > + */ > + if (!pfn_valid(pfn)) > + return VM_FAULT_SIGBUS; Somebody gave us a "struct page", how could the pfn ever by invalid (not have a struct page)? I think all of the above regarding PFNs should be dropped -- unless I am missing something important. > + > + if (WARN_ON(is_zero_pfn(pfn) && write)) > + return VM_FAULT_SIGBUS; is_zero_page() if you already have the "page". But note that in validate_page_before_insert() we do have a check that allows for conditional insertion of the shared zeropage. So maybe this hunk is also not required. > + > + err = insert_page(vma, addr, page, pgprot, write); > + if (err == -ENOMEM) > + return VM_FAULT_OOM; > + if (err < 0 && err != -EBUSY) > + return VM_FAULT_SIGBUS; > + > + return VM_FAULT_NOPAGE; > +} > +EXPORT_SYMBOL_GPL(vmf_insert_page_mkwrite); -- Cheers, David / dhildenb