Re: [PATCH v19 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

[Michał Mirosław]

On Wed, 21 Jun 2023 at 08:35, Muhammad Usama Anjum
<usama.anjum@xxxxxxxxxxxxx> wrote:
> On 6/20/23 11:03 PM, Andrei Vagin wrote:
> ...
> >> +struct pagemap_scan_private {
> >> +    struct page_region *vec_buf, cur_buf;
> >> +    unsigned long long vec_buf_len, vec_buf_index, max_pages, found_pages, flags;
> >
> > should it be just unsigned long?
> These internal values are storing data coming from user in struct
> pm_scan_arg in which all variables are 64 bit(__u64) explicitly. This is
> why we have unsigned long long here. It is absolutely necessary.

vec_buf_len and vec_buf_index can only have values in 0..512 range.
flags has only a few lower bits defined (this is checked on ioctl
entry) and max_pages can be limited to ULONG_MAX. Actually putting `if
(!max_pages || max_pages > ULONG_MAX) max_pages = ULONG_MAX` would
avoid having to check !max_pages during the walk.

Best Regards
Michał Mirosław