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 981B01A6806; Tue, 28 Apr 2026 19:37:06 +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=1777405026; cv=none; b=DlV3231+IuU2KXoZXUsAoBY/ODW1WOWPvqgRVKOnJBQW7rQbw9V8xZ6BRxeHl5WUqO0ai4O9qnaD2E3tGaUPXr7eMZJp/Yio8MyUeColOIqKjbi4iEh7jwcdHrHXzOlNwOFJweU6y5yz8Ki8Aau9kTNLEmNL+elt+PHdlTPtUmg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777405026; c=relaxed/simple; bh=wTu5YsK9WMfcrNfXAKqKVRZWZd07LCagAS8tZcofwKQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Nz4xQwI9mR7YWI/gWygTE/f9tIFyKzqnyIxia7Q6O/C484AWLBVjbACEAaEavLuHqy4bCIpaQeDtnPY1721YQjg+TaU4rf5bppP5HbgYXZAJJjXdfql9hDJ0H6wTs+lDLjeiZghlFlu5SQmwPLmdmqwF3PNQ+m1gxqYnNMKDQJc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oAHXisBD; 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="oAHXisBD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C2A2C2BCAF; Tue, 28 Apr 2026 19:37:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777405026; bh=wTu5YsK9WMfcrNfXAKqKVRZWZd07LCagAS8tZcofwKQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=oAHXisBDzimhXI17wnijGsm4Kj3KwqSSO3NGUOdLz+1w/SMlJbxfKDEcFUM+LzsFH yXZvH7lyhU+H/wQ7YtPQU6R1mIluNmEQJfGAQhC03AFHfmzoYgeIaRcCv5U+NIU77Y xDivJB30dZqPvS+pEFcaZmZrUhsmIEtM4HoaWdZqXxZoTaVYXBUMhB/U9n4GQarLcq SBzJOAhGGVluqLFboRvbHyctyXlY2waiys128tJ5SLSt+OyOM4Rn6Acxvrqj7z5pvQ VljWqC1Oyjx0aGmqK2NgPK1nwwoZ3j4gsd0WUlN8K1CtgK/AzhuDQu4KN6pq6NFeYs foSUkoiGRL5OQ== Message-ID: Date: Tue, 28 Apr 2026 21:36:58 +0200 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] x86/mm: fix freeing of PMD-sized vmemmap pages To: Lance Yang Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, rppt@kernel.org, jgg@ziepe.ca, baolu.lu@linux.intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <20260428-vmemmap-v1-1-b2aa1e6db2c0@kernel.org> <20260428132025.86657-1-lance.yang@linux.dev> 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 4/28/26 15:20, Lance Yang wrote: > > On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote: >> In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched >>from freeing non-boot page tables through __free_pages() to >> pagetable_free(). >> >> However, the function is also called to free vmemmap pages. >> >> Given that vmemmap pages are not page tables, already the page_ptdesc(page) >> is wrong. But worse, pagetable_free() calls >> >> __free_pages(page, compound_order(page)); >> >> As vmemmap pages are not compound pages (see vmemmap_alloc_block()) -- >> except for HVO, which doesn't apply here -- we will only free the first >> page when freeing a PMD-sized vmemmap page, leaking the other ones. >> >> Fix it by properly decoupling pagetable and vmemmap freeing. >> free_pagetable() no longer has to mess with SECTION_INFO, as only the >> vmemmap is marked like that in register_page_bootmem_memmap(). >> >> While at it, just wire up the altmap parameter for remove_pte_table(). >> Also, the indentation in remove_pmd_table() is messed up, let's fix that >> while touching it. >> >> Note that we'll try to get rid of that bootmem info handling soon. For >> now, we'll handle it similar to free_pagetable(), just avoiding the >> ifdef. >> >> Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()") >> Cc: stable@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) >> --- >> Reproduced and tested with a simple VM with a virtio-mem device, >> repeatedly adding and removing memory. >> >> Found by code inspection while working on bootmem_info removal. >> --- > > Cool! I just reproduced the leak with QEMU pc-dimm memory hotplug as > well. > > Without the fix, nr_free_pages kept dropping after the hotplugged memory > was removed again. With the fix applied, it stays stable over repeated > add/remove cycles :) > > Tested-by: Lance Yang Thanks Lance! I'll wait a bit more for feedback, and then resend v2 with the "nr_pages" simplification. -- Cheers, David