linux-kernel - Re: [PATCH 1/2] x86/mm: support memory-failure on 32-bits with SPARSEMEM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251103132358.79766-1-xieyuanbin1@huawei.com>
Date: Mon, 3 Nov 2025 21:23:58 +0800
From: Xie Yuanbin <xieyuanbin1@...wei.com>
To: <tglx@...utronix.de>, <david@...hat.com>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
	<akpm@...ux-foundation.org>, <lorenzo.stoakes@...cle.com>,
	<Liam.Howlett@...cle.com>, <vbabka@...e.cz>, <rppt@...nel.org>,
	<surenb@...gle.com>, <mhocko@...e.com>, <linmiaohe@...wei.com>,
	<nao.horiguchi@...il.com>, <luto@...nel.org>, <peterz@...radead.org>,
	<tony.luck@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-edac@...r.kernel.org>, <will@...nel.org>, <liaohua4@...wei.com>,
	<lilinjie8@...wei.com>, Xie Yuanbin <xieyuanbin1@...wei.com>
Subject: Re: [PATCH 1/2] x86/mm: support memory-failure on 32-bits with SPARSEMEM

On Mon, 3 Nov 2025 13:08:38 +0100, David Hildenbrand wrote:
>> The historical commit d949f36f1865c60239d4 ("x86: Fix hwpoison code
>> related build failure on 32-bit NUMAQ"), disabled x86_32's
>> memory-failure when SPARSEMEM is enabled, because the number of
>> page-flags are insufficient.
>> 
>> The commit 09022bc196d23484a7a5 ("mm: remove PG_error") removes a
>> page flag, so memory-failure can now be enable now.
>
> In the meantime, we added PG_dropbehind

Okay, I completely understand now.

For historical versions, MEMORY_FAILURE cannot be enabled with x86_32 &&
SPARSEMEM because the number of page-flags are insufficient. At least it
has been so from 5.10.x to 6.9.x.

The commit 46df8e73a4a3f1445f2a ("mm: free up PG_slab") from 6.10-rc1
remove a flag that allows MEMORY_FAILURE to be enabled from here on.

The commit 09022bc196d23484a7a5 ("mm: remove PG_error") from 6.12-rc1
remove another flag.

The commit cceba6f7e46c48deca43 ("mm: add PG_dropbehind folio flag") from
6.14-rc1 add a flag, but MEMORY_FAILURE can still be enabled.

At least for the current version, memory-failure can be safely enabled.
The number of pageflags reaches its maximum value under the following
conditions: HIGHMEM && SPARSEMEM && X86_PAE && X86_PAT. In this case, if
MEMORY_FAILURE is enabled, the number of pageflags just reached the limit
of 32.

I will update the V2 patch to describe it.

> Cheers
>
> David / dhildenb

Thanks!

Xie Yuanbin