| Message ID | 20240306104147.193052-2-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/treewide: Remove pXd_huge() API | expand |
On Wed, Mar 06, 2024 at 06:41:35PM +0800, peterx@redhat.com wrote: > From: Peter Xu <peterx@redhat.com> > > Swap pud entries do not always return true for pud_huge() for all archs. > x86 and sparc (so far) allow it, but all the rest do not accept a swap > entry to be reported as pud_huge(). So it's not safe to check swap entries > within pud_huge(). Check swap entries before pud_huge(), so it should be > always safe. > > This is the only place in the kernel that (IMHO, wrongly) relies on > pud_huge() to return true on pud swap entries. The plan is to cleanup > pXd_huge() to only report non-swap mappings for all archs. > > Cc: Alistair Popple <apopple@nvidia.com> > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > mm/hmm.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > @@ -424,7 +424,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > walk->action = ACTION_CONTINUE; > > pud = READ_ONCE(*pudp); > - if (pud_none(pud)) { > + if (pud_none(pud) || !pud_present(pud)) { Isn't this a tautology? pud_none always implies !present() ? Jason
On Thu, Mar 07, 2024 at 02:12:33PM -0400, Jason Gunthorpe wrote: > On Wed, Mar 06, 2024 at 06:41:35PM +0800, peterx@redhat.com wrote: > > From: Peter Xu <peterx@redhat.com> > > > > Swap pud entries do not always return true for pud_huge() for all archs. > > x86 and sparc (so far) allow it, but all the rest do not accept a swap > > entry to be reported as pud_huge(). So it's not safe to check swap entries > > within pud_huge(). Check swap entries before pud_huge(), so it should be > > always safe. > > > > This is the only place in the kernel that (IMHO, wrongly) relies on > > pud_huge() to return true on pud swap entries. The plan is to cleanup > > pXd_huge() to only report non-swap mappings for all archs. > > > > Cc: Alistair Popple <apopple@nvidia.com> > > Signed-off-by: Peter Xu <peterx@redhat.com> > > --- > > mm/hmm.c | 7 +------ > > 1 file changed, 1 insertion(+), 6 deletions(-) > > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> > > > @@ -424,7 +424,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, > > walk->action = ACTION_CONTINUE; > > > > pud = READ_ONCE(*pudp); > > - if (pud_none(pud)) { > > + if (pud_none(pud) || !pud_present(pud)) { > > Isn't this a tautology? pud_none always implies !present() ? Hmm yes I think so, afact, it should be "all=none+swap+present". I still remember I missed that once previously, it's not always obvious when preparing such patches. :( I'll simplify this and also on patch 3. Thanks,
diff --git a/mm/hmm.c b/mm/hmm.c index 277ddcab4947..c44391a0246e 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -424,7 +424,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, walk->action = ACTION_CONTINUE; pud = READ_ONCE(*pudp); - if (pud_none(pud)) { + if (pud_none(pud) || !pud_present(pud)) { spin_unlock(ptl); return hmm_vma_walk_hole(start, end, -1, walk); } @@ -435,11 +435,6 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, unsigned long *hmm_pfns; unsigned long cpu_flags; - if (!pud_present(pud)) { - spin_unlock(ptl); - return hmm_vma_walk_hole(start, end, -1, walk); - } - i = (addr - range->start) >> PAGE_SHIFT; npages = (end - addr) >> PAGE_SHIFT; hmm_pfns = &range->hmm_pfns[i];