Re: [PATCH v25 29/30] mm: Update arch_validate_flags() to include vma anonymous

From: Catalin Marinas
Date: Mon Apr 26 2021 - 07:11:34 EST

On Mon, Apr 26, 2021 at 09:40:56AM +0300, Kirill A. Shutemov wrote:
> On Thu, Apr 15, 2021 at 03:14:18PM -0700, Yu-cheng Yu wrote:
> > When newer VM flags are being created, such as VM_MTE, it becomes necessary
> > for mmap/mprotect to verify if certain flags are being applied to an
> > anonymous VMA.
> >
> > To solve this, one approach is adding a VM flag to track that MAP_ANONYMOUS
> > is specified [1], and then using the flag in arch_validate_flags().
> >
> > Another approach is passing vma_is_anonymous() to arch_validate_flags().
> > To prepare the introduction of PROT_SHSTK, which creates a shadow stack
> > mapping and can only be applied to an anonymous VMA, update arch_validate_
> > flags() to include anonymous VMA information.
> I would rather pass down whole vma. Who knows what else
> arch_validate_flags() would need to know about the VMA tomorrow:
> arch_validate_flags(vma, newflags);
> should do the trick.

A reason why we added a separate VM_MTE_ALLOWED flag was that we wanted
MTE on other RAM-based based mappings, not just anonymous pages. See
51b0bff2f703 ("mm: Allow arm64 mmap(PROT_MTE) on RAM-based files").

Anyway, the above change doesn't get in the way.