On Mon, Jun 08, 2026 at 04:36:51AM -0400, Michael S. Tsirkin wrote: > Now that post_alloc_hook() handles cache-friendly user page > zeroing via folio_zero_user(), convert vma_alloc_zeroed_movable_folio() > to pass __GFP_ZERO instead of zeroing at the callsite. > > Note: before this series, replacing clear_user_highpage() with > __GFP_ZERO was unsafe on cache-aliasing architectures because > __GFP_ZERO uses clear_page() without a dcache flush. With this > series, it is safe if the caller passes a valid user address > (not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers
Wait, so now you're making actual correctness predicated on correctly passing the right user address?? > it to post_alloc_hook() for the dcache flush via > folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed. Yeah, ok I'm beating a dead horse a bit here, but no to this approach. > > Signed-off-by: Michael S. Tsirkin <[email protected]> > Assisted-by: Claude:claude-opus-4-6 > --- > include/linux/highmem.h | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index d7aac9de1c8a..8b0afaabbc6e 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -320,13 +320,8 @@ static inline > struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma, > unsigned long vaddr) > { > - struct folio *folio; > - > - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr); > - if (folio && user_alloc_needs_zeroing()) So now we are unconditionally zeroing the pages even if !user_alloc_needs_zeroing()? You don't mention this in the commit message and it seems like it'll regress performance? > - clear_user_highpage(&folio->page, vaddr); > - > - return folio; > + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, > + 0, vma, vaddr); > } > #endif > > -- > MST > Thanks, Lorenzo
