From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image References: <20200326180730.4754-1-james.morse@arm.com> <20200326180730.4754-2-james.morse@arm.com> <87d088h4k8.fsf@x220.int.ebiederm.org> From: James Morse Message-ID: Date: Wed, 22 Apr 2020 13:28:59 +0100 MIME-Version: 1.0 In-Reply-To: <87d088h4k8.fsf@x220.int.ebiederm.org> Content-Language: en-GB List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: "Eric W. Biederman" Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, linux-mm@kvack.org, Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org Hi Eric, On 15/04/2020 21:33, Eric W. Biederman wrote: > James Morse writes: > >> An image loaded for kexec is not stored in place, instead its segments >> are scattered through memory, and are re-assembled when needed. In the >> meantime, the target memory may have been removed. >> >> Because mm is not aware that this memory is still in use, it allows it >> to be removed. >> >> Add a memory notifier to prevent the removal of memory regions that >> overlap with a loaded kexec image segment. e.g., when triggered from the >> Qemu console: >> | kexec_core: memory region in use >> | memory memory32: Offline failed. >> >> Signed-off-by: James Morse > > Given that we are talking about the destination pages for kexec > not where the loaded kernel is currently stored the description is > confusing. I think David has some better wording to cover this. I thought I had it with 'scattered and re-assembled'. > Beyond that I think it would be better to simply unload the loaded > kernel at memory hotunplug time. Unconditionally, or if it aliases the removed region? I don't particular like it. User-space has asked for two impossible things, we are changing the answer to the first when we see the second. Its a bit spooky. (maybe no one will notice) > Usually somewhere in the loaded image > is a copy of the memory map at the time the kexec kernel was loaded. > That will invalidate the memory map as well. Ah, unconditionally. Sure, x86 needs this. (arm64 re-discovers the memory map from firmware tables after kexec) If that's an acceptable change in behaviour, sure, lets do that. > All of this should be for a very brief window of a few seconds, as > the loaded kexec image is quite short. It seems I'm the outlier anticipating anything could happen between those syscalls. Thanks, James _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec