Re: [PATCH 08/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()

John Hubbard
2019-10-31T23:47:00Z

On 10/31/19 4:35 PM, Ira Weiny wrote:
> On Wed, Oct 30, 2019 at 03:49:19PM -0700, John Hubbard wrote:
>> Convert process_vm_access to use the new pin_user_pages_remote()
>> call, which sets FOLL_PIN. Setting FOLL_PIN is now required for
>> code that requires tracking of pinned pages.
>>
>> Also, release the pages via put_user_page*().
>>
>> Also, rename "pages" to "pinned_pages", as this makes for
>> easier reading of process_vm_rw_single_vec().
>
> Ok... but it made review a bit harder...
>

Yes, sorry about that. After dealing with "pages means struct page *[]"
for all this time, having an "int pages" just was a step too far for
me here. :)

Thanks for working through it.

thanks,

John Hubbard
NVIDIA

> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>

>>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>> mm/process_vm_access.c | 28 +++++++++++++++-------------
>> 1 file changed, 15 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
>> index 357aa7bef6c0..fd20ab675b85 100644
>> --- a/mm/process_vm_access.c
>> +++ b/mm/process_vm_access.c
>> @@ -42,12 +42,11 @@ static int process_vm_rw_pages(struct page **pages,
>> if (copy > len)
>> copy = len;
>>
>> - if (vm_write) {
>> + if (vm_write)
>> copied = copy_page_from_iter(page, offset, copy, iter);
>> - set_page_dirty_lock(page);
>> - } else {
>> + else
>> copied = copy_page_to_iter(page, offset, copy, iter);
>> - }
>> +
>> len -= copied;
>> if (copied < copy && iov_iter_count(iter))
>> return -EFAULT;
>> @@ -96,7 +95,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
>> flags |= FOLL_WRITE;
>>
>> while (!rc && nr_pages && iov_iter_count(iter)) {
>> - int pages = min(nr_pages, max_pages_per_loop);
>> + int pinned_pages = min(nr_pages, max_pages_per_loop);
>> int locked = 1;
>> size_t bytes;
>>
>> @@ -106,14 +105,15 @@ static int process_vm_rw_single_vec(unsigned long addr,
>> * current/current->mm
>> */
>> down_read(&mm->mmap_sem);
>> - pages = get_user_pages_remote(task, mm, pa, pages, flags,
>> - process_pages, NULL, &locked);
>> + pinned_pages = pin_user_pages_remote(task, mm, pa, pinned_pages,
>> + flags, process_pages,
>> + NULL, &locked);
>> if (locked)
>> up_read(&mm->mmap_sem);
>> - if (pages <= 0)
>> + if (pinned_pages <= 0)
>> return -EFAULT;
>>
>> - bytes = pages * PAGE_SIZE - start_offset;
>> + bytes = pinned_pages * PAGE_SIZE - start_offset;
>> if (bytes > len)
>> bytes = len;
>>
>> @@ -122,10 +122,12 @@ static int process_vm_rw_single_vec(unsigned long addr,
>> vm_write);
>> len -= bytes;
>> start_offset = 0;
>> - nr_pages -= pages;
>> - pa += pages * PAGE_SIZE;
>> - while (pages)
>> - put_page(process_pages[--pages]);
>> + nr_pages -= pinned_pages;
>> + pa += pinned_pages * PAGE_SIZE;
>> +
>> + /* If vm_write is set, the pages need to be made dirty: */
>> + put_user_pages_dirty_lock(process_pages, pinned_pages,
>> + vm_write);
>> }
>>
>> return rc;
>> --
>> 2.23.0
>>