From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 342BF2857F0; Wed, 18 Feb 2026 08:01:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771401700; cv=none; b=pffANpq259vIjXLgac4NadV6ZHye/u/DTBYXmR6gN/h/9aRK/WgM3izYZG3QE0jP8x2wPeXNDY7AASlhUoMpmgwnQiAiH+DDtTWZQWVY2pWviY6ZctVWHXoUvmVyVaCN83c0AYTgKzXM7nrH40msJmBY55n1GfH3DeXZKj+xbTY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771401700; c=relaxed/simple; bh=8adjUiJs+jIyBTxznrgbvF6vxedp6JPQT1xLEZRiOgg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DKFZ3hU94JW8GTp/Ydkrrcuj7t2qy4ACst71pgBu1ROSaS0xaS72FxXg9Rt3pU85s+EPC6rOBHYDHkIXcndVXDI5deYqY1852VLQt2FZT9FzvDhCuagDDV7GkVvP3nybDZmUreQNU3kd2xDMvmFfWcD5PjttLgmzQdMqc/gVvJE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Mak/MiUk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mak/MiUk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31D7EC19421; Wed, 18 Feb 2026 08:01:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771401699; bh=8adjUiJs+jIyBTxznrgbvF6vxedp6JPQT1xLEZRiOgg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Mak/MiUkd+UeBgThN5oJMu2tRhUeTEbSkzhtbgGuJ2abeIXAAhw/WSRG9RVeEr5Jy kectQVA4ZvBcEu5IfC1xcl2LwP70llm2OY6xx5vz6Xh+UlGb2Xnbt1IPCg8wtdV0eI OTXlP7aryLb2yWcL9zFI4WO/BinKkUOtJSWZ/B3OIxZLi1TjEOL1JpMvq6p42u9/EX CwE2XevGvDSUf/bj92fb58e8ppKJuHM2y36R4AVnu97jCsOLCMNT/qtwSAQIRXnJD4 /H1DH/dxGW9Xjzc3PYEpnU8f3hbg6XAdMj47rurWmWWOLfcQRax1QJ3RHZVHR5xIuP 5piDRYPkhSgIw== Message-ID: Date: Wed, 18 Feb 2026 09:01:35 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm/huge_memory: fix move_pages_huge_pmd() for huge zero pages To: Chris Down , Andrew Morton Cc: Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/18/26 04:44, Chris Down wrote: > Two fixes for the huge zero page path in move_pages_huge_pmd() > (UFFDIO_MOVE). > > Patch 1 fixes a use of NULL folio introduced by the folio_mk_pmd() > conversion in commit e3981db444a0 ("mm: add folio_mk_pmd()"). > mk_huge_pmd(src_page, ...) with folio_mk_pmd(src_folio, ...) in the huge > zero page branch where src_folio is explicitly NULL. With > SPARSEMEM_VMEMMAP this silently produces a PMD with a bogus PFN, on > other memory models it is a NULL deref. > > Patch 2 adds the missing pmd_mkspecial() call that was omitted when > commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero > folio special") marked huge zero folio PMD mappings as special. Without > it, vm_normal_page_pmd() on CONFIG_ARCH_HAS_PTE_SPECIAL architectures > does not recognise the moved huge zero page as special, incorrectly > treating it as a normal page and corrupting its refcount. Thanks for the report and fixes. This sounds like something selftests should have detected. Can we teach tools/testing/selftests/mm/uffd-unit-tests.c to trigger that behavior on the huge zero folio? We have uffd_move_pmd_test(), but it seems to focus on moving non-zero folios I suppose. -- Cheers, David