Re: [PATCH v4 21/38] uprobes: remove VM_IO, set VM_MIXEDMAP for mapped kernel pages

[Suren Baghdasaryan]

On Sat, Oct 3, 2026 at 6:40 PM Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx> wrote:
>
> These are not MMIO pages so VMA_IO_BIT is an inappropriate flag to set.
>
> Instead, set them VMA_MIXEDMAP_BIT as they are kernel mappings and this is
> the appropriate flag to set for those.
>
> This provides the semantics required - no VMA merging is permitted, but
> does not prevent GUP.
>
> However this has no meaningful impact as these are refcounted and thus can
> be GUPed.
>
> A previous commit already prevented __mm_populate() from being invoked on
> XOL areas, which VMA_IO_BIT was previously relied upon to do, so that is no
> longer required.
>
> Both VMAs set a VMA name, so always_dump_vma() returns true before
> vma_dump_size() reaches its VMA_IO_BIT check, and thus there is no change
> in core dump behaviour.
>
> Change this for both the core xol_add_vma() function and the x86-specific
> get_uprobe_trampoline() function.
>
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>


> ---
>  arch/x86/kernel/uprobes.c | 2 +-
>  kernel/events/uprobes.c   | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 65a2de82ecd2..0f60c0d076b6 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -715,7 +715,7 @@ static struct vm_area_struct *get_uprobe_trampoline(struct mm_struct *mm, unsign
>
>         *new_mapping = true;
>         return _install_special_mapping(mm, vaddr, PAGE_SIZE,
> -                               VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_IO,
> +                               VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_MIXEDMAP,
>                                 &tramp_mapping);
>  }
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 7709ea882477..b89cc5cee002 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1726,8 +1726,8 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
>         }
>
>         vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE,
> -                               VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO|
> -                               VM_SEALED_SYSMAP,
> +                               VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|
> +                               VM_MIXEDMAP|VM_SEALED_SYSMAP,
>                                 &xol_mapping);
>         if (IS_ERR(vma)) {
>                 ret = PTR_ERR(vma);
>
> --
> 2.55.0
>