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Date: Wed, 9 Aug 2023 00:35:01 +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 12:21 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.
>
>> + 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
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