Hi Christoph, On Sat, 25 May 2019 at 14:33, Christoph Hellwig <hch@xxxxxx> wrote: > diff --git a/mm/gup.c b/mm/gup.c > index f173fcbaf1b2..1c21ecfbf38b 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2117,6 +2117,10 @@ static void gup_pgd_range(unsigned long addr, unsigned long end, > } while (pgdp++, addr = next, addr != end); > } > > +#ifndef gup_fixup_start_addr > +#define gup_fixup_start_addr(start) (start) > +#endif As you pointed out in a subsequent reply, we could use the untagged_addr() macro from Andrey (or a shorter "untag_addr" if you want it to look like a verb). > #ifndef gup_fast_permitted > /* > * Check if it's allowed to use __get_user_pages_fast() for the range, or > @@ -2145,7 +2149,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, > unsigned long flags; > int nr = 0; > > - start &= PAGE_MASK; > + start = gup_fixup_start_addr(start) & PAGE_MASK; > len = (unsigned long) nr_pages << PAGE_SHIFT; > end = start + len; > > @@ -2218,7 +2222,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned long addr, len, end; > int nr = 0, ret = 0; > > - start &= PAGE_MASK; > + start = gup_fixup_start_addr(start) & PAGE_MASK; > addr = start; > len = (unsigned long) nr_pages << PAGE_SHIFT; > end = start + len; In Andrey's patch [1] we don't fix __get_user_pages_fast(), only __get_user_pages() as it needs to do a find_vma() search. I wonder whether this is actually necessary for the *_fast() versions. If the top byte is non-zero (i.e. tagged address), 'end' would also have the same tag. The page table macros like pgd_index() and pgd_addr_end() already take care of masking out the top bits (at least for arm64) since they need to work on kernel address with the top bits all 1. So gup_pgd_range() should cope with tagged addresses already. [1] https://lore.kernel.org/lkml/d234cd71774f35229bdfc0a793c34d6712b73093.1557160186.git.andreyknvl@xxxxxxxxxx/ -- Catalin
