[PATCH] fs/proc/task_mmu: move mmu notification mechanism inside mm lock

From: Muhammad Usama Anjum <usama.anjum@collabora.com>
To: "Andrew Morton" <akpm@linux-foundation.org>,
	"David Hildenbrand" <david@redhat.com>,
	"Muhammad Usama Anjum" <usama.anjum@collabora.com>,
	"Andrei Vagin" <avagin@google.com>,
	"Peter Xu" <peterx@redhat.com>, "Hugh Dickins" <hughd@google.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Ryan Roberts" <ryan.roberts@arm.com>,
	"Kefeng Wang" <wangkefeng.wang@huawei.com>,
	"Liam R. Howlett" <Liam.Howlett@Oracle.com>,
	"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
	"Stephen Rothwell" <sfr@canb.auug.org.au>,
	"Arnd Bergmann" <arnd@arndb.de>
Cc: kernel@collabora.com,
	syzbot+81227d2bd69e9dedb802@syzkaller.appspotmail.com,
	Sean Christopherson <seanjc@google.com>,
	stable@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: [PATCH] fs/proc/task_mmu: move mmu notification mechanism inside mm lock
Date: Tue,  9 Jan 2024 16:24:42 +0500	[thread overview]
Message-ID: <20240109112445.590736-1-usama.anjum@collabora.com> (raw)

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.

Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs")
Reported-by: syzbot+81227d2bd69e9dedb802@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/000000000000f6d051060c6785bc@google.com/
Cc: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
 fs/proc/task_mmu.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 62b16f42d5d2..56c2e7357494 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2448,13 +2448,6 @@ static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
 	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_struct *mm, unsigned long uarg)
 		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_struct *mm, unsigned long uarg)
 	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;
 }
-- 
2.42.0

