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Message-ID: <e2967189-84b1-6bcb-9d7f-4c528c06c4bc@collabora.com>
Date: Wed, 9 Aug 2023 09:31:14 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Andrei Vagin <avagin@...il.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>,
Michał Mirosław
<emmir@...gle.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,
Michał Mirosław <mirq-linux@...e.qmqm.pl>
Subject: Re: [PATCH v27 2/6] fs/proc/task_mmu: Implement IOCTL to get and
optionally clear info about PTEs
On 8/9/23 12:55 AM, Andrei Vagin wrote:
> On Tue, Aug 8, 2023 at 12:35 PM Muhammad Usama Anjum
> <usama.anjum@...labora.com> wrote:
>>
>> On 8/9/23 12:21 AM, Andrei Vagin wrote:
>>> On Tue, Aug 8, 2023 at 3:43 AM Muhammad Usama Anjum
>>> <usama.anjum@...labora.com> wrote:
>>>
>>> ....
>>>
>>>> +static int pagemap_scan_output(unsigned long categories,
>>>> + struct pagemap_scan_private *p,
>>>> + unsigned long addr, unsigned long *end)
>>>> +{
>>>> + unsigned long n_pages, total_pages;
>>>> + int ret = 0;
>>>> +
>>>> + if (!p->vec_buf)
>>>> + return 0;
>>>> +
>>>> + categories &= p->arg.return_mask;
>>>> +
>>>> + n_pages = (*end - addr) / PAGE_SIZE;
>>>> + if (check_add_overflow(p->found_pages, n_pages, &total_pages) || //TODO
>>>
>>> Need to fix this TODO.
>> Sorry, I forgot to remove the "//TODO". As far as I've understood, the last
>> discussion ended in keeping the check_add_overflow(). [1] I'll just remove
>> the TODO.
>>
>> https://lore.kernel.org/all/CABb0KFEfmRz+Z_-7GygTL12E5Y254dvoUfWe4uSv9-wOx+Cs8w@mail.gmail.com
>>
>>
>>>
>>>> + total_pages > p->arg.max_pages) {
>>>> + size_t n_too_much = total_pages - p->arg.max_pages;
>>>> + *end -= n_too_much * PAGE_SIZE;
>>>> + n_pages -= n_too_much;
>>>> + ret = -ENOSPC;
>>>> + }
>>>> +
>>>> + if (!pagemap_scan_push_range(categories, p, addr, *end)) {
>>>> + *end = addr;
>>>> + n_pages = 0;
>>>> + ret = -ENOSPC;
>>>> + }
>>>> +
>>>> + p->found_pages += n_pages;
>>>> + if (ret)
>>>> + p->walk_end_addr = *end;
>>>> +
>>>> + return ret;
>>>> +}
>>>> +
>>>
>>> ...
>>>
>>>> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
>>>> +{
>>>> + struct mmu_notifier_range range;
>>>> + struct pagemap_scan_private p;
>>>> + unsigned long walk_start;
>>>> + size_t n_ranges_out = 0;
>>>> + int ret;
>>>> +
>>>> + memset(&p, 0, sizeof(p));
>>>> + ret = pagemap_scan_get_args(&p.arg, uarg);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> + p.masks_of_interest = MASKS_OF_INTEREST(p.arg);
>>>> + ret = pagemap_scan_init_bounce_buffer(&p);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> + /* Protection change for the range is going to happen. */
>>>> + if (p.arg.flags & PM_SCAN_WP_MATCHING) {
>>>> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
>>>> + mm, p.arg.start, p.arg.end);
>>>> + mmu_notifier_invalidate_range_start(&range);
>>>> + }
>>>> +
>>>> + walk_start = p.arg.start;
>>>> + for (; walk_start < p.arg.end; walk_start = p.arg.walk_end) {
>>>> + int n_out;
>>>> +
>>>> + if (fatal_signal_pending(current)) {
>>>> + ret = -EINTR;
>>>> + break;
>>>> + }
>>>> +
>>>> + ret = mmap_read_lock_killable(mm);
>>>> + if (ret)
>>>> + break;
>>>> + ret = walk_page_range(mm, walk_start, p.arg.end,
>>>> + &pagemap_scan_ops, &p);
>>>> + mmap_read_unlock(mm);
>>>> +
>>>> + n_out = pagemap_scan_flush_buffer(&p);
>>>> + if (n_out < 0)
>>>> + ret = n_out;
>>>> + else
>>>> + n_ranges_out += n_out;
>>>> +
>>>> + if (ret != -ENOSPC || p.arg.vec_len - 1 == 0 ||
>>>> + p.found_pages == p.arg.max_pages) {
>>>> + p.walk_end_addr = p.arg.end;
>>>
>>> You should not change p.walk_end_addr If ret is ENOSPC. Pls add a test
>>> case to check this.
>> Yeah, I'm not setting walk_end_addr if ret is ENOSPC.
>>
>> I'm setting walk_end_addr only when ret = 0. I'd added this as a result of
>> a test case in my local test application. I can look at adding some tests
>> in pagemap_ioctl.c kselftest as well.
>
> I am not sure that I understand what you mean here. ENOSPC can be returned
> when the vec array is full and in this case, walk_end_addr should be
> the address when it stops scanning.
I'll copy a test case in kselftest to prove or dis-prove the correctness of
walk_end address.
>
>>
>>>
>>>> + break;
>>>> + }
>>>> + }
>>>> +
>>>> + if (p.cur_buf.start != p.cur_buf.end) {
>>>> + if (copy_to_user(p.vec_out, &p.cur_buf, sizeof(p.cur_buf)))
>>>> + ret = -EFAULT;
>>>> + else
>>>> + ++n_ranges_out;
>>>> + }
>>>> +
>>>> + /* ENOSPC signifies early stop (buffer full) from the walk. */
>>>> + if (!ret || ret == -ENOSPC)
>>>> + ret = n_ranges_out;
>>>> +
>>>> + p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : walk_start;
>>>> + if (pagemap_scan_writeback_args(&p.arg, uarg))
>>>> + ret = -EFAULT;
>>>> +
>>>> + if (p.arg.flags & PM_SCAN_WP_MATCHING)
>>>> + mmu_notifier_invalidate_range_end(&range);
>>>> +
>>>> + kfree(p.vec_buf);
>>>> + return ret;
>>>> +}
>>>
>>> Thanks,
>>> Andrei
>>
>> --
>> BR,
>> Muhammad Usama Anjum
--
BR,
Muhammad Usama Anjum
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