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 0516F2AD00; Wed, 29 Apr 2026 05:50:46 +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=1777441847; cv=none; b=uxMlAXPWTWVhn56cJWl2fApsfV6X/t63RviJWh73qC2aKj4m/awtJODbx+220Rpsdh9GPTvllma5FyOOzgwMuVgmLW7xqnZLWb2faOD8toONVz8N+8W10Y8iIWnFwyL2mfN5Vs0n87GlQrL5X8zMpLTfnWoa53FNF3Uu3WwrYcY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777441847; c=relaxed/simple; bh=s9ptXCgubBcilTQq+jJNC4q9MUiGMDrj0CZmPpJpgd4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NyljN5dKoGw8/9myclu8IU6rcDv93VxFDdL5fPe3utbgSz7GSkg4zwWHdIPkD6mGJ+daXQeyM0Nto4FXIZue27I23VLNuyAyrlIkclwkj9JlJSCTeWewtTaLwW7jmRnF4FAtZKwF4psF7SfVIQ6gSeikZ1NBzzJLeKDemkXF7HY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MZKhV/Et; 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="MZKhV/Et" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A20ECC19425; Wed, 29 Apr 2026 05:50:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777441846; bh=s9ptXCgubBcilTQq+jJNC4q9MUiGMDrj0CZmPpJpgd4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MZKhV/EtmFdCWSgx8/5k65xynUZO3G1bEjmVHu9QPtxdA4JTY9baaFnA/PUDsa0rF DihnGNjXrdDJ/Ypmp13hSRN5hMlwYgg0V4gw3BWkenzNq+4ubqX5FXn4JUv00WLD3O eJ0/c4+pBIEbAIS8gF9coMrZe0vVryYPRiTc8zYpNQavWQMzX+GQvtvyZy8Cw1KQrJ y5r1LpsQgrRLguy/+VNmBIoVLeT1lB7ha2DbOUWeoXS9Y5wNuv4A/+BznGJsY6wzxJ cIOXhfz1GXAQyExcSUKCHMHekOl6qeJ90AXDpLsVgH4+VeT0Fb3cHfMEpQVwlQJE7C FiHTHcDeUcyjw== Message-ID: <3fc697d4-9193-4350-8264-f38ebc4836cc@kernel.org> Date: Wed, 29 Apr 2026 07:50:42 +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> <20260429021224.39916-1-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 4/29/26 04:12, 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. > > One thing I'm not sure about is passing altmap down into > remove_pte_table(). > > Do we actually know that a non-NULL altmap means that the vmemmap > backing page came from that altmap? I thought with an altmap we'd never get into the situation of allocating outside the altmap. But you're right that sub-section hotplug might actually trigger this. > > On x86 we still have in vmemmap_populate(): > > if (end - start < PAGES_PER_SECTION * sizeof(struct page)) > err = vmemmap_populate_basepages(start, end, node, NULL); > > So for smaller-than-section vmemmap ranges, even if the caller has an > altmap, the backing pages are allocated from normal memory. But with > this fix the PTE removal path would now call vmem_altmap_free() just > because altmap is non-NULL, and would not free the actual backing page, > IIUC :) > > Maybe free_vmemmap_pages() should first check that the backing page is > really inside the altmap range before using vmem_altmap_free()? Probably I'll just leave it as is for now, and simply pass "NULL" for the PTE case like we effectively did before. Thanks! -- Cheers, David