linux-kernel - Re: [PATCH v2 0/5] kdump: crashkernel reservation from CMA

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: <2fb04e1b-8ce0-4216-9255-fc09c04e860b@redhat.com>
Date: Fri, 30 May 2025 11:28:01 +0200
From: David Hildenbrand <david@...hat.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Baoquan He <bhe@...hat.com>, Donald Dutile <ddutile@...hat.com>,
 Jiri Bohac <jbohac@...e.cz>, Vivek Goyal <vgoyal@...hat.com>,
 Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org,
 Philipp Rudo <prudo@...hat.com>, Pingfan Liu <piliu@...hat.com>,
 Tao Liu <ltao@...hat.com>, linux-kernel@...r.kernel.org,
 David Hildenbrand <dhildenb@...hat.com>
Subject: Re: [PATCH v2 0/5] kdump: crashkernel reservation from CMA

On 30.05.25 11:26, Michal Hocko wrote:
> On Fri 30-05-25 11:11:40, David Hildenbrand wrote:
>> On 30.05.25 11:07, Michal Hocko wrote:
>>> On Fri 30-05-25 10:39:39, David Hildenbrand wrote:
>>>> On 30.05.25 10:28, Michal Hocko wrote:
>>> [...]
>>>>> All that being said I would go with an additional parameter to the
>>>>> kdump cma setup - e.g. cma_sane_dma that would skip waiting and use 10s
>>>>> otherwise. That would make the optimized behavior opt in, we do not need
>>>>> to support all sorts of timeouts and also learn if this is not
>>>>> sufficient.
>>>>>
>>>>> Makes sense?
>>>>
>>>> Just so I understand correctly, you mean extending the "crashkernel=" option
>>>> with a boolean parameter? If set, e.g., wait 1s, otherwise magic number 10?
>>>
>>> crashkernel=1G,cma,cma_sane_dma # no wait on transition
>>
>> But is no wait ok? I mean, any O_DIRECT with any device would at least take
>> a bit, no?
>>
>> Of course, there is a short time between the crash and actually triggerying
>> kdump.
> 
> This is something we can test for and if we need a short timeout in this
> case as well then it is just trivial to add it. I am much more
> concerned about those potentially unpredictable DMA transfers that could
> take too long and it is impossible to test for those and therefore we
> need to overshoot.

Agreed.

-- 
Cheers,

David / dhildenb