The next patch in this series makes the lockless flow a little more
complex, so move the entire block into a new function and remove a level
of indention. Tidy a bit of cruft:
- addr is always the same as start, so use start
- Use the modern check_add_overflow() for computing end = start + len
- nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to
avoid shift overflow, make the variables unsigned long to avoid coding
casts in both places. nr_pinned was missing its cast
- The handling of ret and nr_pinned can be streamlined a bit
No functional change.
Signed-off-by: Jason Gunthorpe <[email protected]>
---
mm/gup.c | 99 ++++++++++++++++++++++++++++++--------------------------
1 file changed, 54 insertions(+), 45 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 102877ed77a4b4..150cc962c99201 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2671,13 +2671,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
return ret;
}
-static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
+static unsigned long lockless_pages_from_mm(unsigned long start,
+ unsigned long end,
+ unsigned int gup_flags,
+ struct page **pages)
+{
+ unsigned long flags;
+ int nr_pinned = 0;
+
+ if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) ||
+ !gup_fast_permitted(start, end))
+ return 0;
+
+ /*
+ * Disable interrupts. The nested form is used, in order to allow full,
+ * general purpose use of this routine.
+ *
+ * With interrupts disabled, we block page table pages from being freed
+ * from under us. See struct mmu_table_batch comments in
+ * include/asm-generic/tlb.h for more details.
+ *
+ * We do not adopt an rcu_read_lock() here as we also want to block IPIs
+ * that come from THPs splitting.
+ */
+ local_irq_save(flags);
+ gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
+ local_irq_restore(flags);
+ return nr_pinned;
+}
+
+static int internal_get_user_pages_fast(unsigned long start,
+ unsigned long nr_pages,
unsigned int gup_flags,
struct page **pages)
{
- unsigned long addr, len, end;
- unsigned long flags;
- int nr_pinned = 0, ret = 0;
+ unsigned long len, end;
+ unsigned long nr_pinned;
+ int ret;
if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
FOLL_FORCE | FOLL_PIN | FOLL_GET |
@@ -2691,54 +2721,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
might_lock_read(¤t->mm->mmap_lock);
start = untagged_addr(start) & PAGE_MASK;
- addr = start;
- len = (unsigned long) nr_pages << PAGE_SHIFT;
- end = start + len;
-
- if (end <= start)
+ len = nr_pages << PAGE_SHIFT;
+ if (check_add_overflow(start, len, &end))
return 0;
if (unlikely(!access_ok((void __user *)start, len)))
return -EFAULT;
- /*
- * Disable interrupts. The nested form is used, in order to allow
- * full, general purpose use of this routine.
- *
- * With interrupts disabled, we block page table pages from being
- * freed from under us. See struct mmu_table_batch comments in
- * include/asm-generic/tlb.h for more details.
- *
- * We do not adopt an rcu_read_lock(.) here as we also want to
- * block IPIs that come from THPs splitting.
- */
- if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) {
- unsigned long fast_flags = gup_flags;
-
- local_irq_save(flags);
- gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned);
- local_irq_restore(flags);
- ret = nr_pinned;
- }
+ nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
+ if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
+ return nr_pinned;
- if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) {
- /* Try to get the remaining pages with get_user_pages */
- start += nr_pinned << PAGE_SHIFT;
- pages += nr_pinned;
-
- ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned,
- gup_flags, pages);
-
- /* Have to be a bit careful with return values */
- if (nr_pinned > 0) {
- if (ret < 0)
- ret = nr_pinned;
- else
- ret += nr_pinned;
- }
+ /* Slow path: try to get the remaining pages with get_user_pages */
+ start += nr_pinned << PAGE_SHIFT;
+ pages += nr_pinned;
+ ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags,
+ pages);
+ if (ret < 0) {
+ /*
+ * The caller has to unpin the pages we already pinned so
+ * returning -errno is not an option
+ */
+ if (nr_pinned)
+ return nr_pinned;
+ return ret;
}
-
- return ret;
+ return ret + nr_pinned;
}
+
/**
* get_user_pages_fast_only() - pin user pages in memory
* @start: starting user address
--
2.28.0
On Fri 30-10-20 11:46:20, Jason Gunthorpe wrote:
> The next patch in this series makes the lockless flow a little more
> complex, so move the entire block into a new function and remove a level
> of indention. Tidy a bit of cruft:
>
> - addr is always the same as start, so use start
>
> - Use the modern check_add_overflow() for computing end = start + len
>
> - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to
> avoid shift overflow, make the variables unsigned long to avoid coding
> casts in both places. nr_pinned was missing its cast
>
> - The handling of ret and nr_pinned can be streamlined a bit
>
> No functional change.
>
> Signed-off-by: Jason Gunthorpe <[email protected]>
Looks good to me. You can add:
Reviewed-by: Jan Kara <[email protected]>
Honza
> ---
> mm/gup.c | 99 ++++++++++++++++++++++++++++++--------------------------
> 1 file changed, 54 insertions(+), 45 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 102877ed77a4b4..150cc962c99201 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2671,13 +2671,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
> return ret;
> }
>
> -static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
> +static unsigned long lockless_pages_from_mm(unsigned long start,
> + unsigned long end,
> + unsigned int gup_flags,
> + struct page **pages)
> +{
> + unsigned long flags;
> + int nr_pinned = 0;
> +
> + if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) ||
> + !gup_fast_permitted(start, end))
> + return 0;
> +
> + /*
> + * Disable interrupts. The nested form is used, in order to allow full,
> + * general purpose use of this routine.
> + *
> + * With interrupts disabled, we block page table pages from being freed
> + * from under us. See struct mmu_table_batch comments in
> + * include/asm-generic/tlb.h for more details.
> + *
> + * We do not adopt an rcu_read_lock() here as we also want to block IPIs
> + * that come from THPs splitting.
> + */
> + local_irq_save(flags);
> + gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
> + local_irq_restore(flags);
> + return nr_pinned;
> +}
> +
> +static int internal_get_user_pages_fast(unsigned long start,
> + unsigned long nr_pages,
> unsigned int gup_flags,
> struct page **pages)
> {
> - unsigned long addr, len, end;
> - unsigned long flags;
> - int nr_pinned = 0, ret = 0;
> + unsigned long len, end;
> + unsigned long nr_pinned;
> + int ret;
>
> if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
> FOLL_FORCE | FOLL_PIN | FOLL_GET |
> @@ -2691,54 +2721,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
> might_lock_read(¤t->mm->mmap_lock);
>
> start = untagged_addr(start) & PAGE_MASK;
> - addr = start;
> - len = (unsigned long) nr_pages << PAGE_SHIFT;
> - end = start + len;
> -
> - if (end <= start)
> + len = nr_pages << PAGE_SHIFT;
> + if (check_add_overflow(start, len, &end))
> return 0;
> if (unlikely(!access_ok((void __user *)start, len)))
> return -EFAULT;
>
> - /*
> - * Disable interrupts. The nested form is used, in order to allow
> - * full, general purpose use of this routine.
> - *
> - * With interrupts disabled, we block page table pages from being
> - * freed from under us. See struct mmu_table_batch comments in
> - * include/asm-generic/tlb.h for more details.
> - *
> - * We do not adopt an rcu_read_lock(.) here as we also want to
> - * block IPIs that come from THPs splitting.
> - */
> - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) {
> - unsigned long fast_flags = gup_flags;
> -
> - local_irq_save(flags);
> - gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned);
> - local_irq_restore(flags);
> - ret = nr_pinned;
> - }
> + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
> + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
> + return nr_pinned;
>
> - if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) {
> - /* Try to get the remaining pages with get_user_pages */
> - start += nr_pinned << PAGE_SHIFT;
> - pages += nr_pinned;
> -
> - ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned,
> - gup_flags, pages);
> -
> - /* Have to be a bit careful with return values */
> - if (nr_pinned > 0) {
> - if (ret < 0)
> - ret = nr_pinned;
> - else
> - ret += nr_pinned;
> - }
> + /* Slow path: try to get the remaining pages with get_user_pages */
> + start += nr_pinned << PAGE_SHIFT;
> + pages += nr_pinned;
> + ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags,
> + pages);
> + if (ret < 0) {
> + /*
> + * The caller has to unpin the pages we already pinned so
> + * returning -errno is not an option
> + */
> + if (nr_pinned)
> + return nr_pinned;
> + return ret;
> }
> -
> - return ret;
> + return ret + nr_pinned;
> }
> +
> /**
> * get_user_pages_fast_only() - pin user pages in memory
> * @start: starting user address
> --
> 2.28.0
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
On 10/30/20 7:46 AM, Jason Gunthorpe wrote:
> The next patch in this series makes the lockless flow a little more
> complex, so move the entire block into a new function and remove a level
> of indention. Tidy a bit of cruft:
>
> - addr is always the same as start, so use start
>
> - Use the modern check_add_overflow() for computing end = start + len
>
> - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to
> avoid shift overflow, make the variables unsigned long to avoid coding
> casts in both places. nr_pinned was missing its cast
>
> - The handling of ret and nr_pinned can be streamlined a bit
>
> No functional change.
>
> Signed-off-by: Jason Gunthorpe <[email protected]>
> ---
> mm/gup.c | 99 ++++++++++++++++++++++++++++++--------------------------
> 1 file changed, 54 insertions(+), 45 deletions(-)
Everything still looks correct.
Reviewed-by: John Hubbard <[email protected]>
thanks,
--
John Hubbard
NVIDIA
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 102877ed77a4b4..150cc962c99201 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2671,13 +2671,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
> return ret;
> }
>
> -static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
> +static unsigned long lockless_pages_from_mm(unsigned long start,
> + unsigned long end,
> + unsigned int gup_flags,
> + struct page **pages)
> +{
> + unsigned long flags;
> + int nr_pinned = 0;
> +
> + if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) ||
> + !gup_fast_permitted(start, end))
> + return 0;
> +
> + /*
> + * Disable interrupts. The nested form is used, in order to allow full,
> + * general purpose use of this routine.
> + *
> + * With interrupts disabled, we block page table pages from being freed
> + * from under us. See struct mmu_table_batch comments in
> + * include/asm-generic/tlb.h for more details.
> + *
> + * We do not adopt an rcu_read_lock() here as we also want to block IPIs
> + * that come from THPs splitting.
> + */
> + local_irq_save(flags);
> + gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
> + local_irq_restore(flags);
> + return nr_pinned;
> +}
> +
> +static int internal_get_user_pages_fast(unsigned long start,
> + unsigned long nr_pages,
> unsigned int gup_flags,
> struct page **pages)
> {
> - unsigned long addr, len, end;
> - unsigned long flags;
> - int nr_pinned = 0, ret = 0;
> + unsigned long len, end;
> + unsigned long nr_pinned;
> + int ret;
>
> if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
> FOLL_FORCE | FOLL_PIN | FOLL_GET |
> @@ -2691,54 +2721,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
> might_lock_read(¤t->mm->mmap_lock);
>
> start = untagged_addr(start) & PAGE_MASK;
> - addr = start;
> - len = (unsigned long) nr_pages << PAGE_SHIFT;
> - end = start + len;
> -
> - if (end <= start)
> + len = nr_pages << PAGE_SHIFT;
> + if (check_add_overflow(start, len, &end))
> return 0;
> if (unlikely(!access_ok((void __user *)start, len)))
> return -EFAULT;
>
> - /*
> - * Disable interrupts. The nested form is used, in order to allow
> - * full, general purpose use of this routine.
> - *
> - * With interrupts disabled, we block page table pages from being
> - * freed from under us. See struct mmu_table_batch comments in
> - * include/asm-generic/tlb.h for more details.
> - *
> - * We do not adopt an rcu_read_lock(.) here as we also want to
> - * block IPIs that come from THPs splitting.
> - */
> - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) {
> - unsigned long fast_flags = gup_flags;
> -
> - local_irq_save(flags);
> - gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned);
> - local_irq_restore(flags);
> - ret = nr_pinned;
> - }
> + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
> + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
> + return nr_pinned;
>
> - if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) {
> - /* Try to get the remaining pages with get_user_pages */
> - start += nr_pinned << PAGE_SHIFT;
> - pages += nr_pinned;
> -
> - ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned,
> - gup_flags, pages);
> -
> - /* Have to be a bit careful with return values */
> - if (nr_pinned > 0) {
> - if (ret < 0)
> - ret = nr_pinned;
> - else
> - ret += nr_pinned;
> - }
> + /* Slow path: try to get the remaining pages with get_user_pages */
> + start += nr_pinned << PAGE_SHIFT;
> + pages += nr_pinned;
> + ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags,
> + pages);
> + if (ret < 0) {
> + /*
> + * The caller has to unpin the pages we already pinned so
> + * returning -errno is not an option
> + */
> + if (nr_pinned)
> + return nr_pinned;
> + return ret;
> }
> -
> - return ret;
> + return ret + nr_pinned;
> }
> +
> /**
> * get_user_pages_fast_only() - pin user pages in memory
> * @start: starting user address
>
On Fri, Oct 30, 2020 at 11:46:20AM -0300, Jason Gunthorpe wrote:
> The next patch in this series makes the lockless flow a little more
> complex, so move the entire block into a new function and remove a level
> of indention. Tidy a bit of cruft:
>
> - addr is always the same as start, so use start
>
> - Use the modern check_add_overflow() for computing end = start + len
>
> - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to
> avoid shift overflow, make the variables unsigned long to avoid coding
> casts in both places. nr_pinned was missing its cast
>
> - The handling of ret and nr_pinned can be streamlined a bit
>
> No functional change.
>
> Signed-off-by: Jason Gunthorpe <[email protected]>
Sorry for a very late reply (due to other distractions):
Reviewed-by: Peter Xu <[email protected]>
Thanks,
--
Peter Xu