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TgfTxR2GRWtXYiwfhLQCyBuOsUoy+E66xLKAzkumHmSofqC6kjVED2Jbvj4Flm2mFuvtK8Pf/9Ipe61lD5+GsxQygiZcHtRGn79vJhAEkCgXlWe20Cu9BAIemk2n35VG6c1wpaKQj2mfW6DLnyNF6vKV4Wtyl7UqnwVWs60dnxwayknAAbReZwLx+hkijQd+TyWqKvCFyIZx345IoTADnUHkzWOAfK+v4jT5pIrKPbCuM7PrrejNC7nHInEgPd9BajOwSCKz7f2ObJIHcP7FnJ5AVQvfNWOfhcTr+uKZxbMpqaaXA2NvLUJP7sUxwD1LEIwZ2LEutl88xeBeYk+ggP5uLBrXjp7mxGGLPmMPjMTBHBQuaIUiYV4q+XtGSvwLBv6YrrKwL3e4BUi48V1c6mnQ16gkFOHaE1S2Tww2TcEPb0V/g27/MCE53UdIHaIIr6oWUME5VpsZy8InEoqFJ9TXmLyfYw6A829Xl38g4NCutka1jBoxVqVvfKNeBymPAue6r8kQ6o0kQhbU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/24/26 3:29 PM, Rik van Riel wrote: > check_vma_flags() rejects a VMA whose flags gup cannot handle. A caller > that wants to reach a COWed page in a VM_IO or VM_PFNMAP VMA, where that > page does have a struct page, cannot express the exception and has to > repeat the flag test itself. > > Add an ignore_flags argument that check_vma_flags() clears from its local > copy of vma->vm_flags before the flag checks. A caller can drop a single > rejection this way while keeping every other check. All current callers > pass 0. > > This prepares for get_user_page_vma(), which passes VM_IO | VM_PFNMAP to > reach those COWed pages. > > No functional change intended. > > Assisted-by: Claude:claude-opus-4.8 > Signed-off-by: Rik van Riel > --- > mm/gup.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 0692119b7904..dcece7b5253c 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1197,13 +1197,21 @@ static bool writable_file_mapping_allowed(struct vm_area_struct *vma, > return !vma_needs_dirty_tracking(vma); > } > > -static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) > +static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags, > + vm_flags_t ignore_flags) All callers pass zero in this patch, so there is no behavior change yet. The problem is the interface being added. The same local vm_flags value is used for the VM_IO/VM_PFNMAP gate, VM_WRITE, VM_SHADOW_STACK, VM_READ, VM_MAYREAD, and is_cow_mapping(). An arbitrary mask can therefore alter permission, shadow-stack, and COW validation. For example, masking VM_SHARED changes the result of is_cow_mapping(), while masking VM_SHADOW_STACK removes its write rejection. Checks implemented through helpers still read the original vma->vm_flags, so the meaning of ignore_flags also depends on how each check happens to be implemented. Perhaps it is best to replace the mask with a single-purpose internal GUP flag, such as FOLL_PFNMAP_COW, and apply it only to the special-mapping gate: if (vm_flags & (VM_IO | VM_PFNMAP) && (!(gup_flags & FOLL_PFNMAP_COW) || !(vm_flags & VM_PFNMAP))) return -EFAULT; This permits the later caller to examine a VM_PFNMAP mapping while keeping VM_IO-only mappings and every other VMA check unchanged. thanks, -- John Hubbard