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Sat, 17 Oct 2026 02:26:00 +0000 X-Mizu-Trace-ID: 67a546fd69196711 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.12\)) Subject: Re: [PATCH] mm: warn on unaligned compound zone device ranges From: Muchun Song In-Reply-To: <20261016192111.cf4b6477a13a711248a8a079@linux-foundation.org> Date: Sat, 17 Oct 2026 10:25:42 +0800 Cc: Muchun Song , Mike Rapoport , Dan Williams , Vishal Verma , Dave Jiang , Alison Schofield , Joao Martins , Ritesh Harjani , linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <869C8763-FB8C-41B2-957E-0AD1B22FCC57@linux.dev> References: <20261016131334.3419393-1-songmuchun@bytedance.com> <20261016192111.cf4b6477a13a711248a8a079@linux-foundation.org> To: Andrew Morton X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 4C0221C0004 X-Stat-Signature: 4pk4ymzeg8x7ow1o34rx5ooubx1sc49q X-HE-Tag: 1792203962-305297 X-HE-Meta: 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 RcmYdhzS 6iPGBhG4v1nOT+iksbWYc9DvH5W0ULeum4RInnOfBHML7yG9zk6WB/V6+jrD/YUQ7UnuxKd+R9S8QXUFGibEK0WEGzA19XSDLFTs3y/9oi2pj5Xg/aQPKqxOg3dj5JIhfNu9909bUi3ytRvnRV9vpq1nBirQt3+ceK/q5wLEOmz57KrVsJlG8bVDAdLt6CuERQCkcQ/v+TEcrCQDBZDxrK6Ub0qZHxyq3yJNk7SLIVZLZZrC8iAGNjYeohjtNb7SQJExkAtoRWhUKZXxnm5gio9vgU9V7EvKrQzk7ttvQRW7ItFjuUxSlMaw8r2Wukc9RE1N6dQehT0QtCic+IkQFlFM7HBrGeV2LQf9jPlGugWMjJ4CSq4KT+ypemd+r/3ZEKMr2DO82KN5q5/zwS+ROI0o62zH9POB0iSmANLtr7Xlc1ok= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Oct 17, 2026, at 10:21, Andrew Morton = wrote: >=20 > On Fri, 16 Oct 2026 21:13:34 +0800 Muchun Song = wrote: >=20 >> A compound page of order N must start at a PFN aligned to 2^N pages. >> Therefore, a range used to initialize compound pages must start on a >> compound-page boundary and contain an integral number of compound = pages. >>=20 >> Two recent Device DAX bugs were caused by ranges that violated this >> invariant, but neither was detected by memmap_init_zone_device(). >>=20 >> Warn if the adjusted zone-device range violates this invariant so = future >> violations are reported when the compound pages are initialized. >>=20 >> ... >>=20 >> --- a/mm/mm_init.c >> +++ b/mm/mm_init.c >> @@ -1142,6 +1142,8 @@ void __ref memmap_init_zone_device(struct zone = *zone, >> if (!nr_pages) >> return; >>=20 >> + VM_WARN_ON(!IS_ALIGNED(start_pfn | nr_pages, = pfns_per_compound)); >=20 > Would VM_WARN_ON_ONCE() suffice? What I was thinking is that this function won't be called frequently, so = it won't encounter a large volume of log flushing. Therefore, I didn't use = the ONCE interface, and this way it can continue to catch similar issues. I'm OK if you prefer VM_WARN_ON_ONCE() though. Let me know what you = think. Thanks, Muchun >=20 >> + >> /* >> * Seed the reusable head-page template from the first real = struct >> * page. The normal page-init and refcount helpers must operate = on >>=20 >> base-commit: 63562804f25cb5b6f5e4f5e3a9f0d1c3c6868596 >> --=20 >> 2.54.0