linux-kernel - Re: [PATCH v20 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

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Message-ID: <de16602a-7ed9-9c03-30d9-5edccc48d2f0@collabora.com>
Date:   Wed, 21 Jun 2023 19:16:07 +0500
From:   Muhammad Usama Anjum <usama.anjum@...labora.com>
To:     Michał Mirosław <emmir@...gle.com>
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrei Vagin <avagin@...il.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Yun Zhou <yun.zhou@...driver.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Alex Sierra <alex.sierra@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: Re: [PATCH v20 2/5] fs/proc/task_mmu: Implement IOCTL to get and
 optionally clear info about PTEs

On 6/21/23 6:42 PM, Michał Mirosław wrote:
> On Wed, 21 Jun 2023 at 09:24, Muhammad Usama Anjum
> <usama.anjum@...labora.com> wrote:
> [...]
>> +static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
>> +                                 struct mm_walk *walk)
>> +{
>> +       struct pagemap_scan_private *p = walk->private;
>> +       struct vm_area_struct *vma = walk->vma;
>> +
>> +       if ((p->flags & PM_SCAN_REQUIRE_UFFD) && (!userfaultfd_wp_async(vma) ||
>> +           !userfaultfd_wp_use_markers(vma)))
>> +               return -EPERM;
>> +
>> +       if (vma->vm_flags & VM_PFNMAP)
>> +               return 1;
>> +
>> +       return 0;
>> +}
> 
> This could actually short-circuit all vma flags (e.g. IS_FILE): if
> (required_mask & IS_FILE && vma is not file-backed) return 0;
Sorry, unable to understand you. Should we do something here?

> 
> Best Regards
> Michał Mirosław

-- 
BR,
Muhammad Usama Anjum