2019-06-13 15:35:36

by Pingfan Liu

Subject: [PATCHv4 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path

FOLL_LONGTERM suggests a pin which is going to be given to hardware and
can't move. It would truncate CMA permanently and should be excluded.

FOLL_LONGTERM has already been checked in the slow path, but not checked in
the fast path, which means a possible leak of CMA page to longterm pinned
requirement through this crack.

Place a check in gup_pte_range() in the fast path.

Signed-off-by: Pingfan Liu <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: [email protected]
---
mm/gup.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 766ae54..de1b03f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1757,6 +1757,14 @@ 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);

+ /*
+ * FOLL_LONGTERM suggests a pin given to hardware. Prevent it
+ * from truncating CMA area
+ */
+ if (unlikely(flags & FOLL_LONGTERM) &&
+ is_migrate_cma_page(page))
+ goto pte_unmap;
+
head = try_get_compound_head(page, 1);
if (!head)
goto pte_unmap;
@@ -1900,6 +1908,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);

+ if (unlikely(flags & FOLL_LONGTERM) &&
+ is_migrate_cma_page(page)) {
+ *nr -= refs;
+ return 0;
+ }
+
head = try_get_compound_head(pmd_page(orig), refs);
if (!head) {
*nr -= refs;
@@ -1941,6 +1955,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);

+ if (unlikely(flags & FOLL_LONGTERM) &&
+ is_migrate_cma_page(page)) {
+ *nr -= refs;
+ return 0;
+ }
+
head = try_get_compound_head(pud_page(orig), refs);
if (!head) {
*nr -= refs;
@@ -1978,6 +1998,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
refs++;
} while (addr += PAGE_SIZE, addr != end);

+ if (unlikely(flags & FOLL_LONGTERM) &&
+ is_migrate_cma_page(page)) {
+ *nr -= refs;
+ return 0;
+ }
+
head = try_get_compound_head(pgd_page(orig), refs);
if (!head) {
*nr -= refs;
--
2.7.5

2019-06-13 21:38:28

by Ira Weiny

Subject: Re: [PATCHv4 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path

On Thu, Jun 13, 2019 at 06:45:01PM +0800, Pingfan Liu wrote:
> FOLL_LONGTERM suggests a pin which is going to be given to hardware and
> can't move. It would truncate CMA permanently and should be excluded.
>
> FOLL_LONGTERM has already been checked in the slow path, but not checked in
> the fast path, which means a possible leak of CMA page to longterm pinned
> requirement through this crack.
>
> Place a check in gup_pte_range() in the fast path.
>
> Signed-off-by: Pingfan Liu <[email protected]>
> Cc: Ira Weiny <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Mike Rapoport <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Matthew Wilcox <[email protected]>
> Cc: John Hubbard <[email protected]>
> Cc: "Aneesh Kumar K.V" <[email protected]>
> Cc: Keith Busch <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Shuah Khan <[email protected]>
> Cc: [email protected]
> ---
> mm/gup.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 766ae54..de1b03f 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1757,6 +1757,14 @@ 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);
>
> + /*
> + * FOLL_LONGTERM suggests a pin given to hardware. Prevent it
> + * from truncating CMA area
> + */
> + if (unlikely(flags & FOLL_LONGTERM) &&
> + is_migrate_cma_page(page))
> + goto pte_unmap;
> +
> head = try_get_compound_head(page, 1);
> if (!head)
> goto pte_unmap;
> @@ -1900,6 +1908,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> refs++;
> } while (addr += PAGE_SIZE, addr != end);
>
> + if (unlikely(flags & FOLL_LONGTERM) &&
> + is_migrate_cma_page(page)) {
> + *nr -= refs;
> + return 0;
> + }
> +

Why can't we place this check before the while loop and skip subtracting the
page count?

Can is_migrate_cma_page() operate on any "subpage" of a compound page?

Here this calls is_magrate_cma_page() on the tail page of the compound page.

I'm not an expert on compound pages nor cma handling so is this ok?

It seems like you need to call is_migrate_cma_page() on each page within the
while loop?

> head = try_get_compound_head(pmd_page(orig), refs);
> if (!head) {
> *nr -= refs;
> @@ -1941,6 +1955,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> refs++;
> } while (addr += PAGE_SIZE, addr != end);
>
> + if (unlikely(flags & FOLL_LONGTERM) &&
> + is_migrate_cma_page(page)) {
> + *nr -= refs;
> + return 0;
> + }
> +

Same comment here.

> head = try_get_compound_head(pud_page(orig), refs);
> if (!head) {
> *nr -= refs;
> @@ -1978,6 +1998,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> refs++;
> } while (addr += PAGE_SIZE, addr != end);
>
> + if (unlikely(flags & FOLL_LONGTERM) &&
> + is_migrate_cma_page(page)) {
> + *nr -= refs;
> + return 0;
> + }
> +

And here.

Ira

> head = try_get_compound_head(pgd_page(orig), refs);
> if (!head) {
> *nr -= refs;
> --
> 2.7.5
>

2019-06-14 15:25:20

by Pingfan Liu

Subject: Re: [PATCHv4 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path

Cc Mike, David, who is an expert of hugetlb and thp

On Fri, Jun 14, 2019 at 5:37 AM Ira Weiny <[email protected]> wrote:
>
> On Thu, Jun 13, 2019 at 06:45:01PM +0800, Pingfan Liu wrote:
> > FOLL_LONGTERM suggests a pin which is going to be given to hardware and
> > can't move. It would truncate CMA permanently and should be excluded.
> >
> > FOLL_LONGTERM has already been checked in the slow path, but not checked in
> > the fast path, which means a possible leak of CMA page to longterm pinned
> > requirement through this crack.
> >
> > Place a check in gup_pte_range() in the fast path.
> >
> > Signed-off-by: Pingfan Liu <[email protected]>
> > Cc: Ira Weiny <[email protected]>
> > Cc: Andrew Morton <[email protected]>
> > Cc: Mike Rapoport <[email protected]>
> > Cc: Dan Williams <[email protected]>
> > Cc: Matthew Wilcox <[email protected]>
> > Cc: John Hubbard <[email protected]>
> > Cc: "Aneesh Kumar K.V" <[email protected]>
> > Cc: Keith Busch <[email protected]>
> > Cc: Christoph Hellwig <[email protected]>
> > Cc: Shuah Khan <[email protected]>
> > Cc: [email protected]
> > ---
> > mm/gup.c | 26 ++++++++++++++++++++++++++
> > 1 file changed, 26 insertions(+)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 766ae54..de1b03f 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1757,6 +1757,14 @@ 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);
> >
> > + /*
> > + * FOLL_LONGTERM suggests a pin given to hardware. Prevent it
> > + * from truncating CMA area
> > + */
> > + if (unlikely(flags & FOLL_LONGTERM) &&
> > + is_migrate_cma_page(page))
> > + goto pte_unmap;
> > +
> > head = try_get_compound_head(page, 1);
> > if (!head)
> > goto pte_unmap;
> > @@ -1900,6 +1908,12 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> > refs++;
> > } while (addr += PAGE_SIZE, addr != end);
> >
> > + if (unlikely(flags & FOLL_LONGTERM) &&
> > + is_migrate_cma_page(page)) {
> > + *nr -= refs;
> > + return 0;
> > + }
> > +
>
> Why can't we place this check before the while loop and skip subtracting the
> page count?
Yes, that will be better.

>
> Can is_migrate_cma_page() operate on any "subpage" of a compound page?
For gigantic page, __alloc_gigantic_page() allocate from
MIGRATE_MOVABLE pageblock. For page order < MAX_ORDER, pages are
allocated from either free_list[MIGRATE_MOVABLE] or
free_list[MIGRATE_CMA]. So all subpage have the same migrate type.

Thanks,
Pingfan
>
> Here this calls is_magrate_cma_page() on the tail page of the compound page.
>
> I'm not an expert on compound pages nor cma handling so is this ok?
>
> It seems like you need to call is_migrate_cma_page() on each page within the
> while loop?
>
> > head = try_get_compound_head(pmd_page(orig), refs);
> > if (!head) {
> > *nr -= refs;
> > @@ -1941,6 +1955,12 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> > refs++;
> > } while (addr += PAGE_SIZE, addr != end);
> >
> > + if (unlikely(flags & FOLL_LONGTERM) &&
> > + is_migrate_cma_page(page)) {
> > + *nr -= refs;
> > + return 0;
> > + }
> > +
>
> Same comment here.
>
> > head = try_get_compound_head(pud_page(orig), refs);
> > if (!head) {
> > *nr -= refs;
> > @@ -1978,6 +1998,12 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> > refs++;
> > } while (addr += PAGE_SIZE, addr != end);
> >
> > + if (unlikely(flags & FOLL_LONGTERM) &&
> > + is_migrate_cma_page(page)) {
> > + *nr -= refs;
> > + return 0;
> > + }
> > +
>
> And here.
>
> Ira
>
> > head = try_get_compound_head(pgd_page(orig), refs);
> > if (!head) {
> > *nr -= refs;
> > --
> > 2.7.5
> >