On 7/29/26 18:48, Lorenzo Stoakes (ARM) wrote:
> We must correctly update VMA anonymous page offset state on all VMA
> operations that would result in it changing, with special attention given
> to remapping.
>
> We cover most cases by simply updating vma_set_range() to do so (with a new
> anonymous page offset parameter), but also notably must update the merging
> and mapping logic to propagate this parameter correctly.
>
> The remap logic remains the same - we may update the anonymous page offset
> if the VMA is unfaulted, but now this applies to MAP_PRIVATE file-backed
> mappings too, so we update the code to reflect this.
>
> Note that we use __linear_anon_page_index() upon remap as the VMA may be
> shared, in order that we update the field consistently regardless of VMA
> type.
>
> Similarly, pass through anon page offset to the merge logic, updating the
> vma_merge_struct struct to propagate it, and also use
> __linear_anon_page_index() to obtain the anonymous page index so it can be
> safely used for both shared and MAP_PRIVATE file-backed mappings.
>
> Finally, we update insert_vm_struct() to correctly set the anonymous page
> offset on insertion of a VMA.
>
> We simply ensure state is correctly propagated here, so no functional
> changes are intended.
>
> Also while we're here, replace a VM_BUG_ON_VMA() with a
> VM_WARN_ON_ONCE_VMA().
>
> Also update VMA userland tests to reflect this change.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
[...]
> struct vm_area_struct *vma = *vmap;
> unsigned long vma_start = vma->vm_start;
> @@ -1919,11 +1929,14 @@ struct vm_area_struct *copy_vma(struct vm_area_struct
> **vmap,
> VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);
>
> /*
> - * If anonymous vma has not yet been faulted, update new pgoff
> - * to match new location, to increase its chance of merging.
> + * If a vma has not yet been faulted, update its anonymous pgoff to
> + * match the new location to increase its chance of merging.
> */
> - if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
> - pgoff = addr >> PAGE_SHIFT;
> + if (!vma->anon_vma && !vma_test(vma, VMA_SHARED_BIT)) {
Could we also use is_cow_mapping() ?
> + anon_pgoff = addr >> PAGE_SHIFT;
> +
> + if (vma_is_anonymous(vma))
> + pgoff = anon_pgoff;
> faulted_in_anon_vma = false;
> }
>
Acked-by: David Hildenbrand (Arm) <[email protected]>
--
Cheers,
David
