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b=bJyrtF7/OFk+pS/31wbvaD/xB7Rv/k9KDyiU6nymD22iIq9ByUeQhJMkhcoxZxBvF T8XbpglCc0oyk5HIVB0rFQEQi4FYz25Tjhg9LazpnjtwnljsZVdPxfdkkBEpY4phyg +1pQAolnanUVT5H5FyT1s9kkMj6evH1jJP7gJpiQ= Date: Mon, 25 May 2026 12:10:41 -0700 From: Andrew Morton To: Nico Pache Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support Message-Id: <20260525121041.2f2508a4f627c338cddd837a@linux-foundation.org> In-Reply-To: <2b2cda8c-358a-4a5c-989c-ae42593ef2ea@redhat.com> References: <20260522150009.121603-1-npache@redhat.com> <20260522150009.121603-12-npache@redhat.com> <2b2cda8c-358a-4a5c-989c-ae42593ef2ea@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 5wu8icppw7kd7k39djjzbzb7zz5s7kw8 X-Rspamd-Queue-Id: D3BEE80010 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1779736244-572383 X-HE-Meta: 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 R5BCxzc4 ISCe3/sStaXcL0w+PtufDUQcm2ZUSs2AZn4/HHgSBagrfKNFlAWM3R9D51vumLHASmjL3GHU8VHA+bS+8ufBRfFTbN9V4FgCRvF34/ExIAtRlY6XmuylV0S/er7zn2p8Isxj0/w20YWXI2rWD7r+sWXJ78kKWPk8lNF0ljw9SyGSt1BzigmKcGEhHqCqyU6aGwTDrb/tJcu8UxqgIwM1Y/W27JzA7JEaaBXj8CkmR88ZjUO9FaXsQPFnQ2fnxGCZVj4GWNkV27A4stDFslHIHsqVltQfX5K2+5+VoyrlxeI5sB/r5FlbwcR7mupC2WZ0PBmCTRr93YUDwitTd1vicI0g43BexXpoyd8B4QpEwvSx7w/c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 25 May 2026 08:15:53 -0600 Nico Pache wrote: > Can you please append the following fixup that reverts one of the > changes requested in V17. The issue with the change is described > below. OK. fyi, what I received was badly mangled: wordwrapping, tabs messed up, etc. Here's my reconstruction: Author: Nico Pache Subject: fix potential use-after-free of vma in mthp_collapse() Date:=A0Mon May 25 07:38:59 2026 -0600 Between V17 and v18, one reviewer (Wei) brought up that we are not doing the uffd-armed check until deep in the collapse operation. While not functionally incorrect, it can lead to unnecessary work. We optimized this by passing the vma variable to mthp_collapse() and using the collapse_max_ptes_none() function to check the state of uffd-armed preventing the wasted work later in the collapse. mthp_collapse() is called after mmap_read_unlock(), so the vma pointer can become stale. Remove the vma parameter and pass NULL to collapse_max_ptes_none() instead. Link: https://lore.kernel.org/2b2cda8c-358a-4a5c-989c-ae42593ef2ea@redhat.c= om Signed-off-by: Nico Pache ... mm/khugepaged.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) --- a/mm/khugepaged.c~mm-khugepaged-introduce-mthp-collapse-support-fix +++ a/mm/khugepaged.c @@ -1502,9 +1502,9 @@ static unsigned int collapse_mthp_count_ * If a collapse is permitted, we attempt to collapse the PTE range into a * mTHP. */ -static int mthp_collapse(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long address, int referenced, int unmapped, - struct collapse_control *cc, unsigned long enabled_orders) +static int mthp_collapse(struct mm_struct *mm, unsigned long address, + int referenced, int unmapped, struct collapse_control *cc, + unsigned long enabled_orders) { unsigned int nr_occupied_ptes, nr_ptes, max_ptes_none; int collapsed =3D 0, stack_size =3D 0; @@ -1524,7 +1524,7 @@ static int mthp_collapse(struct mm_struc if (!test_bit(order, &enabled_orders)) goto next_order; =20 - max_ptes_none =3D collapse_max_ptes_none(cc, vma, order); + max_ptes_none =3D collapse_max_ptes_none(cc, NULL, order); =20 nr_occupied_ptes =3D collapse_mthp_count_present(cc, offset, nr_ptes); @@ -1749,7 +1749,7 @@ out_unmap: if (result =3D=3D SCAN_SUCCEED) { /* collapse_huge_page expects the lock to be dropped before calling */ mmap_read_unlock(mm); - nr_collapsed =3D mthp_collapse(mm, vma, start_addr, referenced, + nr_collapsed =3D mthp_collapse(mm, start_addr, referenced, unmapped, cc, enabled_orders); /* mmap_lock was released above, set lock_dropped */ *lock_dropped =3D true; _