| Message ID | 20210420131611.8259-2-rppt@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | secretmem: optimize page_is_secretmem() | expand |
On 20.04.21 15:16, Mike Rapoport wrote: > From: Mike Rapoport <rppt@linux.ibm.com> > > The check in gup_pte_range() whether a page belongs to a secretmem mapping > is performed before grabbing the page reference. > > To avoid potential race move the check after try_grab_compound_head(). > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > --- > mm/gup.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index c3a17b189064..4b58c016e949 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > > - if (page_is_secretmem(page)) > - goto pte_unmap; > - > head = try_grab_compound_head(page, 1, flags); > if (!head) > goto pte_unmap; > > + if (page_is_secretmem(page)) > + goto pte_unmap; > + Looking at the hunk below, I wonder if you're missing a put_compound_head(). (also, I'd do if unlikely(page_is_secretmem()) but that's a different discussion) > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > put_compound_head(head, 1, flags); > goto pte_unmap; >
On Tue, Apr 20, 2021 at 03:19:56PM +0200, David Hildenbrand wrote: > On 20.04.21 15:16, Mike Rapoport wrote: > > From: Mike Rapoport <rppt@linux.ibm.com> > > > > The check in gup_pte_range() whether a page belongs to a secretmem mapping > > is performed before grabbing the page reference. > > > > To avoid potential race move the check after try_grab_compound_head(). > > > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > > --- > > mm/gup.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/mm/gup.c b/mm/gup.c > > index c3a17b189064..4b58c016e949 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > > page = pte_page(pte); > > - if (page_is_secretmem(page)) > > - goto pte_unmap; > > - > > head = try_grab_compound_head(page, 1, flags); > > if (!head) > > goto pte_unmap; > > + if (page_is_secretmem(page)) > > + goto pte_unmap; > > + > > Looking at the hunk below, I wonder if you're missing a put_compound_head(). Hmm, yes. > (also, I'd do if unlikely(page_is_secretmem()) but that's a different > discussion) I don't mind, actually. I don't think there would be massive secretmem usage soon. > > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > > put_compound_head(head, 1, flags); > > goto pte_unmap; > > > > > -- > Thanks, > > David / dhildenb >
diff --git a/mm/gup.c b/mm/gup.c index c3a17b189064..4b58c016e949 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); - if (page_is_secretmem(page)) - goto pte_unmap; - head = try_grab_compound_head(page, 1, flags); if (!head) goto pte_unmap; + if (page_is_secretmem(page)) + goto pte_unmap; + if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_compound_head(head, 1, flags); goto pte_unmap;