On Fri, May 15, 2026 at 11:39:20AM -0400, Gregory Price wrote: > On Thu, May 14, 2026 at 03:08:13PM -0400, Michael S. Tsirkin wrote: > > On Thu, May 14, 2026 at 02:56:54PM -0400, Gregory Price wrote: > > > 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 :] > > > > Hmm. Are you sure? Isn't the address used for numa policy? > > > > You said "They do not allocate userspace pages" - so wouldn't uaddr be > USER_ADDR_NONE anyway?
That part was wrong. > > Even if they do allocate userspace pages, they weren't passing > __GFP_ZERO before, so either: > > 1) They did not depend on the buddy to do zeroing before, and > user_addr is just a dead variable in those cases anyway. > > or > > 2) There is a bug, and they should be zeroing the page. IIUC, it's neither. Consider CoW: yes we are allocating a new page for userspace, but no we do not need to zero: we are copying data on write. > I just see an interesting hardening opportunity. > > Not suggesting you actually implement this, to be clear, maybe just > documenting the idea on the thread as a potential follow up. > > ~Gregory
