On Mon, Jun 08, 2026 at 11:40:02AM +0100, Lorenzo Stoakes wrote: > 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?
OK sorry I see in 12/37 you do this there instead. > > > - clear_user_highpage(&folio->page, vaddr); > > - > > - return folio; > > + return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, > > + 0, vma, vaddr); > > } > > #endif > > > > -- > > MST > > > > Thanks, Lorenzo
