+ mm-memory-add-vmf_insert_page_mkwrite.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/memory: add vmf_insert_page_mkwrite()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memory-add-vmf_insert_page_mkwrite.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-add-vmf_insert_page_mkwrite.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alistair Popple <apopple@nvidia.com>
Subject: mm/memory: add vmf_insert_page_mkwrite()
Date: Tue, 7 Jan 2025 14:42:29 +1100

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.

Link: https://lkml.kernel.org/r/0b56d4b4da706ef6e7194b1776fda54ed4c21599.1736221254.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |    2 ++
 mm/memory.c        |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

--- a/include/linux/mm.h~mm-memory-add-vmf_insert_page_mkwrite
+++ a/include/linux/mm.h
@@ -3627,6 +3627,8 @@ int vm_map_pages(struct vm_area_struct *
 				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,
--- a/mm/memory.c~mm-memory-add-vmf_insert_page_mkwrite
+++ a/mm/memory.c
@@ -2622,6 +2622,42 @@ static vm_fault_t __vm_insert_mixed(stru
 	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));
+
+	if (!pfn_modify_allowed(pfn, pgprot))
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * We refcount the page normally so make sure pfn_valid is true.
+	 */
+	if (!pfn_valid(pfn))
+		return VM_FAULT_SIGBUS;
+
+	if (WARN_ON(is_zero_pfn(pfn) && write))
+		return VM_FAULT_SIGBUS;
+
+	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);
+
 vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
 		pfn_t pfn)
 {
_

Patches currently in -mm which might be from apopple@nvidia.com are

fuse-fix-dax-truncate-punch_hole-fault-path.patch
fs-dax-return-unmapped-busy-pages-from-dax_layout_busy_page_range.patch
fs-dax-dont-skip-locked-entries-when-scanning-entries.patch
fs-dax-refactor-wait-for-dax-idle-page.patch
fs-dax-create-a-common-implementation-to-break-dax-layouts.patch
fs-dax-always-remove-dax-page-cache-entries-when-breaking-layouts.patch
fs-dax-ensure-all-pages-are-idle-prior-to-filesystem-unmount.patch
fs-dax-remove-page_mapping_dax_shared-mapping-flag.patch
mm-gup-remove-redundant-check-for-pci-p2pdma-page.patch
mm-mm_init-move-p2pdma-page-refcount-initialisation-to-p2pdma.patch
mm-allow-compound-zone-device-pages.patch
mm-memory-enhance-insert_page_into_pte_locked-to-create-writable-mappings.patch
mm-memory-add-vmf_insert_page_mkwrite.patch
rmap-add-support-for-pud-sized-mappings-to-rmap.patch
huge_memory-add-vmf_insert_folio_pud.patch
huge_memory-add-vmf_insert_folio_pmd.patch
memremap-add-is_devdax_page-and-is_fsdax_page-helpers.patch
mm-gup-dont-allow-foll_longterm-pinning-of-fs-dax-pages.patch
proc-task_mmu-mark-devdax-and-fsdax-pages-as-always-unpinned.patch
mm-mlock-skip-zone_device-pmds-during-mlock.patch
fs-dax-properly-refcount-fs-dax-pages.patch
device-dax-properly-refcount-device-dax-pages-when-mapping.patch
mm-remove-pxx_devmap-callers.patch
mm-remove-devmap-related-functions-and-page-table-bits.patch
revert-riscv-mm-add-support-for-zone_device.patch