linux-kernel - Re: [PATCH v13 7/7] x86/crash: add x86 crash hotplug support

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: <ad35b9b1-447e-c65e-a083-13a8e36c8a5a@oracle.com>
Date:   Wed, 9 Nov 2022 16:12:24 -0600
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v13 7/7] x86/crash: add x86 crash hotplug support



On 11/9/22 15:31, Borislav Petkov wrote:
> On Wed, Nov 09, 2022 at 09:48:33AM -0600, Eric DeVolder wrote:
>> ...
>> which then defaults HOTPLUG_CPU to on and thus this code/ifdef in question.
> 
> defconfig can sometimes lag reality. In this case, the majority of
> machines have SMP=y because the majority of machines out there are,
> well, multicore.
> 
>> So at this point, I'm still not sure if you want the ifdef line:
>>   - removed altogether
>>   - transitioned to CRASH_HOTPLUG
>>   - leave as is
> 
> So let's think out loud:
> 
> * the majority of machines will have CONFIG_HOTPLUG_CPU=y because
> they're SMP machines and we want the elfcorehdr updates to happen when
> CPUs get offlined or onlined.
> 
> CONFIG_MEMORY_HOTPLUG is most likely going to be =n on the majority of
> machines out there.
> 
> (Note how the deciding factor for all this is what would make sense on
> the prevailing majority of machines out there.)
> 
> And memory hotplug will be off for the simple reason that not so many
> machines have memory hotplug hardware capability.
> 
> Which then means, IMHO, this functionality should be separate: have a
> CPU hotplug callback and a memory hotplug callback.
> 
> And you kinda do that in
> 
> Subject: [PATCH v13 3/7] crash: add generic infrastructure for crash hotplug support
> 
> but then this all calls into a single handle_hotplug_event() and that
> hp_action doesn't really matter.
> 
> It is used in the call to
> 
>    arch_crash_handle_hotplug_event(image, hp_action);
> 
> but that hp_action argument is unused in the x86 version. >
> IOW, you can do this callback regardless whether it is a CPU or memory
> hotplug event.
> 
> So thinking about it, a single CONFIG_CRASH_HOTPLUG which unifies those
> CPU and memory hotplug callback functionality makes most sense to me.
> Because you don't really differentiate between the two in the callback
> actions.
> 
> Anyway, this is how I see it from here. I could very well be missing an
> aspect, of course.
> 
> Thx.
> 
OK, I'll put in CRASH_HOTPLUG! Expect v14 soon!
Thank you!
eric