linux-kernel - Re: [PATCH 6/6] cxl/sysram: disallow onlining in ZONE

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] [day] [month] [year] [list]

Message-ID: <988ca415-ea91-4509-8552-5b8829d9e8f0@amd.com>
Date: Tue, 13 Jan 2026 16:35:02 -0600
From: "Cheatham, Benjamin" <benjamin.cheatham@....com>
To: Gregory Price <gourry@...rry.net>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel-team@...a.com>, <dave@...olabs.net>, <jonathan.cameron@...wei.com>,
	<dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
	<dan.j.williams@...el.com>, David Hildenbrand <david@...nel.org>, "Hannes
 Reinecke" <hare@...e.de>
Subject: Re: [PATCH 6/6] cxl/sysram: disallow onlining in ZONE_NORMAL if state
 is movable only

On 1/12/2026 5:14 PM, Gregory Price wrote:
> On Mon, Jan 12, 2026 at 03:11:05PM -0600, Cheatham, Benjamin wrote:
>> On 1/12/2026 10:35 AM, Gregory Price wrote:
>>> If state is set to online (default to ZONE_MOVABLE), the user intends
>>> for this memory to either refuse non-movable allocations, and/or intends
>>> to preserve the hot-unpluggability of this memory.  However, any admin
>>> can write `offline` and `online` to the memory block controller and
>>> bring that memory online in ZONE_NORMAL.
>>
>> Is it the expectation that the user will never want to change the zone from
>> MOVABLE to NORMAL? I can't think of a reason someone would want to off the top
>> of my head, but I also can't think of a reason to restrict it either.
>>
> 
> It's more to restrict this pattern
> 
> echo online_movable > region0/hotplug
>    -> creates:   node1/memory123/
> 
> echo offline > node1/memory123/state
> echo online > node1/memory123/state
> 
> The result of this would be valid_zones=[normal movable], which would
> break hot-unplug.

Ahh ok I think I get it now. I wasn't thinking about bypassing the memctrl/ interface
and using the memory block sysfs directly. Thanks for the explanation!

Thanks,
Ben

> 
>>> If an actor attempts to online the block into ZONE_NORMAL, it will fail,
>>> but if it attempts to online into either NORMAL or MOVABLE, only MOVABLE
>>> will be allowed and it will succeed.
>>
>> I'm not sure you need this paragraph. I think it's a logical conclusion of the above
>> that if someone attempts to online the memory as NORMAL or MOVABLE it'll only be onlined
>> as MOVABLE.
> 
> in the above situation the following occurs:
> 
> echo online  > region0/hotplug
> echo offline > node1/memory123/state
> echo online  > node1/memory123/state
> cat node1/memory123/valid_zones
>    normal movable
> echo offline > node1/memory123/state
> echo 1  > node1/memory123/online
> cat node1/memory123/valid_zones
>    normal
> 
> 
> echo online_movable  > region0/hotplug
> echo offline > node1/memory123/state
> echo online  > node1/memory123/state
> cat node1/memory123/valid_zones
>    movable
> echo offline > node1/memory123/state
> echo 1  > node1/memory123/online
>    fail with EXXXX (i forget what code)
> 
> It's a little confusing.
> 
>>> +	switch (data->last_online_type) {
>>> +	case MMOP_ONLINE_MOVABLE:
>>> +		return sysfs_emit(buf, "online\n");
>>> +	case MMOP_ONLINE_KERNEL:
>>> +		return sysfs_emit(buf, "online_normal\n");
>>> +	case MMOP_OFFLINE:
>>> +	default:
>>
>> You're missing the MMOP_ONLINE case. In that case the memory would be reported as "offline", which
>> I doubt is the intention.
>>
> 
> Blah, i originally had all of them and just reduced to
> MMOP_ONLINE_MOVABLE and MMOP_ONLINE (i don't see a good use for
> MMOP_ONLINE_KERNEL), but i'll fix this up.
> 
> Thanks!
> Gregory