The patch titled Subject: fs/proc/task_mmu: move mmu notification mechanism inside mm lock has been added to the -mm mm-hotfixes-unstable branch. Its filename is fs-proc-task_mmu-move-mmu-notification-mechanism-inside-mm-lock.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Muhammad Usama Anjum usama.anjum@collabora.com Subject: fs/proc/task_mmu: move mmu notification mechanism inside mm lock Date: Tue, 9 Jan 2024 16:24:42 +0500

Move mmu notification mechanism inside mm lock to prevent race condition in other components which depend on it. The notifier will invalidate memory range. Depending upon the number of iterations, different memory ranges would be invalidated.

The following warning would be removed by this patch: WARNING: CPU: 0 PID: 5067 at arch/x86/kvm/../../../virt/kvm/kvm_main.c:734 kvm_mmu_notifier_change_pte+0x860/0x960 arch/x86/kvm/../../../virt/kvm/kvm_main.c:734

There is no behavioural and performance change with this patch when there is no component registered with the mmu notifier.

Link: https://lkml.kernel.org/r/20240109112445.590736-1-usama.anjum@collabora.com Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") Signed-off-by: Muhammad Usama Anjum usama.anjum@collabora.com Reported-by: syzbot+81227d2bd69e9dedb802@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/000000000000f6d051060c6785bc@google.com/ Reviewed-by: Sean Christopherson seanjc@google.com Cc: Andrei Vagin avagin@google.com Cc: Arnd Bergmann arnd@arndb.de Cc: David Hildenbrand david@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: Liam R. Howlett Liam.Howlett@oracle.com Cc: Micha�� Miros��aw mirq-linux@rere.qmqm.pl Cc: Peter Xu peterx@redhat.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/proc/task_mmu.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)

--- a/fs/proc/task_mmu.c~fs-proc-task_mmu-move-mmu-notification-mechanism-inside-mm-lock +++ a/fs/proc/task_mmu.c @@ -2448,13 +2448,6 @@ static long do_pagemap_scan(struct mm_st 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); - } - for (walk_start = p.arg.start; walk_start < p.arg.end; walk_start = p.arg.walk_end) { long n_out; @@ -2467,8 +2460,20 @@ static long do_pagemap_scan(struct mm_st ret = mmap_read_lock_killable(mm); if (ret) break; + + /* 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, walk_start, p.arg.end); + mmu_notifier_invalidate_range_start(&range); + } + ret = walk_page_range(mm, walk_start, p.arg.end, &pagemap_scan_ops, &p); + + if (p.arg.flags & PM_SCAN_WP_MATCHING) + mmu_notifier_invalidate_range_end(&range); + mmap_read_unlock(mm);

n_out = pagemap_scan_flush_buffer(&p); @@ -2494,9 +2499,6 @@ static long do_pagemap_scan(struct mm_st 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; } _

Patches currently in -mm which might be from usama.anjum@collabora.com are

fs-proc-task_mmu-move-mmu-notification-mechanism-inside-mm-lock.patch