Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image

From: David Hildenbrand <david@redhat.com>
To: Baoquan He <bhe@redhat.com>
Cc: piliu@redhat.com, Anshuman Khandual <anshuman.khandual@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Bhupesh Sharma <bhsharma@redhat.com>,
	linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	linux-mm@kvack.org, James Morse <james.morse@arm.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image
Date: Thu, 16 Apr 2020 15:31:40 +0200	[thread overview]
Message-ID: <18cf6afd-c651-25c7-aca3-3ca3c0e07547@redhat.com> (raw)
In-Reply-To: <20200415023524.GG4247@MiWiFi-R3L-srv>

> Not sure if I get the notifier idea clearly. If you mean 
> 
> 1) Add a common function to pick memory in unmovable zone;

Not strictly required IMHO. But, minor detail.

> 2) Let DLPAR, balloon register with notifier;

Yeah, or virtio-mem, or any other technology that adds/removes memory
dynamically.

> 3) In the common function, ask notified part to check if the picked
>    unmovable memory is available for locating kexec kernel;

Yeah.

> 
> Sounds doable to me, and not complicated.
> 
>> images. It would apply to
>>
>> - arm64 and filter out all hotadded memory (IIRC, only boot memory can
>>   be used).
> 
> Do you mean hot added memory after boot can't be recognized and added
> into system RAM on arm64?

See patch #3 of this patch set, which wants to avoid placing kexec
binaries on hotplugged memory. But I have no idea what the current plan
regarding arm64 is (this thread exploded :) ).

I would assume that we don't want to place kexec images on any
hotplugged (or rather: hot(un)pluggable) memory - on any architecture.

> 
> 
>> - powerpc to filter out all LMBs that can be removed (assuming not all
>>   memory corresponds to LMBs that can be removed, otherwise we're in
>>   trouble ... :) )
>> - virtio-mem to filter out all memory it added.
>> - hyper-v to filter out partially backed memory blocks (esp. the last
>>   memory block it added and only partially backed it by memory).
>>
>> This would make it work for kexec_file_load(), however, I do wonder how
>> we would want to approach that from userspace kexec-tools when handling
>> it from kexec_load().
> 
> Let's make kexec_file_load work firstly. Since this work is only first
> step to make kexec-ed kernel not break memory hotplug. After kexec
> rebooting, the KASLR may locate kernel into hotpluggable area too.

Can you elaborate how that would work?

-- 
Thanks,

David / dhildenb

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel