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From:   =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <emmir@google.com>
Date:   Wed, 21 Jun 2023 15:29:20 +0200
Message-ID: <CABb0KFHpE+jJH0MmxZTFaQ9FNFNUnJcnnv7sSGDYqDqqB_FRqw@mail.gmail.com>
Subject: Re: [PATCH v19 2/5] fs/proc/task_mmu: Implement IOCTL to get and
 optionally clear info about PTEs
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     Andrei Vagin <avagin@gmail.com>, Peter Xu <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Danylo Mocherniuk <mdanylo@google.com>,
        Paul Gofman <pgofman@codeweavers.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>,
        Yun Zhou <yun.zhou@windriver.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Alex Sierra <alex.sierra@amd.com>,
        Matthew Wilcox <willy@infradead.org>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>, kernel@collabora.com
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On Wed, 21 Jun 2023 at 08:35, Muhammad Usama Anjum
<usama.anjum@collabora.com> wrote:
> On 6/20/23 11:03=E2=80=AFPM, 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_p=
ages, 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 =3D ULONG_MAX` would
avoid having to check !max_pages during the walk.

Best Regards
Micha=C5=82 Miros=C5=82aw