On Thu, May 14, 2026 at 02:00:31PM -0400, Michael S. Tsirkin wrote:
> On Thu, May 14, 2026 at 09:49:33AM -0400, Gregory Price wrote:
>
> There are calls with no __GFP_ZERO but they do not allocate userspace pages.
>
> - drm_pagemap.c: GFP_HIGHUSER -- no zero. But this is a DRM device
> page migration, the page content is preserved from the source.
>
> - test_hmm.c: GFP_HIGHUSER_MOVABLE -- no zero. Test driver, pages get
> content from device.
>
> - mm/ksm.c: GFP_HIGHUSER_MOVABLE -- no zero. KSM merges identical
> pages, content comes from the source page (copy).
>
> - mm/memory.c new_folio = GFP_HIGHUSER_MOVABLE
> - no zero. This is CoW, content is copied from old page.
>
> - mm/userfaultfd.c: GFP_HIGHUSER_MOVABLE - no zero. Content comes from
> userspace via userfaultfd.
>
> - arm64/fault.c: __GFP_ZEROTAGS not __GFP_ZERO. MTE tag zeroing, not page
> zeroing. Page is zeroed separately.
>
Right, so in all of these cases, it would be just as correct to pass
USER_ADDR_NONE I imagine :]
i.e. the user address is irrelevant, and the caller is responsible for
sanitization before return if it's relevant.
Otherwise, passing (user_addr != -1) the buddy takes care of it for you.
Just an obvious security bonus to all of this, but by no means a
requirement for your set. Just an observation.
>
> I'd do this on top if possible.
>
Yeah reasonable.
~Gregory
