From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5AFFB37C900 for ; Fri, 11 Sep 2026 18:01:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789149714; cv=none; b=eAAnwdB6xZ4Bv7kVMPNjl6JYsdh69aZXSSsYyPTRlUj3zVc8zLRV7jGXiMQW5XcQtpuJrXpExzuBdD0U5NqzH1QjBbY9y9IygpjhPn4TpBZFntHbf7LrONbCwKSWjM9e58YzO2Tbj7UjKVzqF7SKRhCITYAr64OZKhB63c49GlQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789149714; c=relaxed/simple; bh=JUYInO57Kd2QrYVqmjJiEtmS5h4fB1SJFnB0mCaTuQg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kErcj0gGQaBLYGSAH0hmMWkX8j7FMhOpAUuuJKwDxsjYzAGOTw0N/Mnq2XUYcY29YdmS/UBGtBB3ubUzRrHgT5b2elpXbL5tpO405Vq7iAusMznAvnTmuL/ZHAJqUcdtPzn7a9BEJdshSE2dVUMIacdR5sohTjM3YeG0eLvLkdI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NAoHBUUC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NAoHBUUC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9287A1F000FF; Fri, 11 Sep 2026 18:01:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789149713; bh=qhIWTcm0FYDnzyosqjyVmJ5CwqqhLKGSIdHrmte54X4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NAoHBUUC6iTOhnfEiRIL2ybzUIvjYJUlufJ6P2HXRugjhUvN0oxbF1Rz1J2+UVesd MSwhOvljnoikab8xv4GX4VgZJF3oY+jtQfYnKrlwYz/QhLJpTraFTE/LeyKhiHGpn9 xNzwctdLeHSap4lro0YBpoKyHLYc5FumKwa1e4HDWvhGykBEURMyMj6ySXwOEFY7wP idWqFcZgUE01OaMdEebblpkci77+WDc4G4qjLUh9nlqyebO5HzerVaHmIkBOd8NRK4 sKqJlmoX4ZelnHyyToErLTLBswdG823/SOgoLLThHRV8K4ZmOWwM3dUWWpOTewDYe4 sdSuyGymWGzVQ== Message-ID: <664b3576-05a9-4c49-99c6-ba0928b25300@kernel.org> Date: Fri, 11 Sep 2026 20:01:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: consolidate compound folio handling To: Hui Su , Andrew Morton Cc: Matthew Brost , Balbir Singh , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260911061348.2869524-1-sh_def@163.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/11/26 08:13, Hui Su wrote: > Commit dc41e961a269 ("mm/migrate_device: avoid out-of-bounds writes for > compound folios") added handling for compound folios that do not fit in > the remaining PFN array. > > migrate_device_range() and migrate_device_pfns() duplicate the logic for > locking device PFNs, encoding compound folios, and handling this boundary > condition. > > A compound folio cannot be represented partially for migration. Warn when > one does not fit in the remaining PFN array, while retaining the existing > defensive handling: release any lock and reference acquired for the > current folio, clear the remaining entries, and stop collecting. > > Move the shared collection and encoding logic into a helper so both > interfaces handle compound folios consistently. Also use memset() for > the compound-folio tail entries instead of open-coding the clearing loop. > > Document that an encountered compound folio must fit entirely in the > remaining range or PFN array. > > Link: https://lore.kernel.org/r/c99ca53a-73ef-4a0c-8738-eba1cc89bea2@kernel.org > Suggested-by: David Hildenbrand > Signed-off-by: Hui Su > --- > Tested on x86_64 with KASAN enabled: > > - Built mm/migrate_device.o and the kernel successfully. > - Ran the HMM migrate_anon_huge_zero selftest; the private-device case > passed. > - No KASAN report or truncated compound-folio WARN was observed. > > mm/migrate_device.c | 90 ++++++++++++++++++++++++--------------------- > 1 file changed, 49 insertions(+), 41 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 009bfa8b212d..c57eadea6565 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1392,6 +1392,39 @@ static unsigned long migrate_device_pfn_lock(unsigned long pfn) > return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; > } > > +/* > + * Collect a device folio into the page-granular PFN array. > + * > + * Return the number of entries consumed, or 0 if the folio does not fit in > + * the remaining array. > + */ > +static unsigned int migrate_device_collect_folio(unsigned long *src_pfn, > + unsigned long pfn, > + unsigned long remaining) Two tab indent please. > +{ > + struct folio *folio = page_folio(pfn_to_page(pfn)); > + unsigned int nr; > + > + *src_pfn = migrate_device_pfn_lock(pfn); > + nr = folio_nr_pages(folio); > + > + if (WARN_ON_ONCE(nr > remaining)) { Just to be sure: there is no way we can currently validly trigger this, right? > + if (*src_pfn & MIGRATE_PFN_MIGRATE) { > + folio_unlock(folio); > + folio_put(folio); > + } > + memset(src_pfn, 0, remaining * sizeof(*src_pfn)); > + return 0; > + } > + > + if (nr > 1) { > + *src_pfn |= MIGRATE_PFN_COMPOUND; > + memset(src_pfn + 1, 0, (nr - 1) * sizeof(*src_pfn)); > + } > + > + return nr; > +} Looks much cleaner. -- Cheers, David