Re: [PATCH v6 12/26] mm/memory: Enhance insert_page_into_pte_locked() to create writable mappings
From: David Hildenbrand <hidden>
Date: 2025-01-14 15:03:35
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On 10.01.25 07:00, Alistair Popple wrote:
quoted hunk ↗ jump to hunk
In preparation for using insert_page() for DAX, enhance insert_page_into_pte_locked() to handle establishing writable mappings. Recall that DAX returns VM_FAULT_NOPAGE after installing a PTE which bypasses the typical set_pte_range() in finish_fault. Signed-off-by: Alistair Popple <apopple@nvidia.com> Suggested-by: Dan Williams <redacted> --- Changes for v5: - Minor comment/formatting fixes suggested by David Hildenbrand Changes since v2: - New patch split out from "mm/memory: Add dax_insert_pfn" --- mm/memory.c | 37 +++++++++++++++++++++++++++++-------- 1 file changed, 29 insertions(+), 8 deletions(-)diff --git a/mm/memory.c b/mm/memory.c index 06bb29e..8531acb 100644 --- a/mm/memory.c +++ b/mm/memory.c@@ -2126,19 +2126,40 @@ static int validate_page_before_insert(struct vm_area_struct *vma, } static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte, - unsigned long addr, struct page *page, pgprot_t prot) + unsigned long addr, struct page *page, + pgprot_t prot, bool mkwrite) { struct folio *folio = page_folio(page); + pte_t entry = ptep_get(pte); pte_t pteval;
> Just drop "entry" and reuse "pteval"; even saves you from one bug below :) pte_t pteval = ptep_get(pte);
- if (!pte_none(ptep_get(pte)))
- return -EBUSY;
+ if (!pte_none(entry)) {
+ if (!mkwrite)
+ return -EBUSY;
+
+ /* see insert_pfn(). */
+ if (pte_pfn(entry) != page_to_pfn(page)) {
+ WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry)));
+ return -EFAULT;
+ }
+ entry = maybe_mkwrite(entry, vma);
+ entry = pte_mkyoung(entry);
+ if (ptep_set_access_flags(vma, addr, pte, entry, 1))
+ update_mmu_cache(vma, addr, pte);
+ return 0;
+ }
+
/* Ok, finally just insert the thing.. */
pteval = mk_pte(page, prot);
if (unlikely(is_zero_folio(folio))) {
pteval = pte_mkspecial(pteval);
} else {
folio_get(folio);
+ entry = mk_pte(page, prot);we already do "pteval = mk_pte(page, prot);" above? And I think your change here does not do what you want, because you modify the new "entry" but we do set_pte_at(vma->vm_mm, addr, pte, pteval); below ...
+ if (mkwrite) {
+ entry = pte_mkyoung(entry);
+ entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+ }So again, better just reuse pteval :) -- Cheers, David / dhildenb