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Tue, 14 Apr 2020 14:49:30 +0000 (UTC) Received: from [10.36.113.201] (ovpn-113-201.ams2.redhat.com [10.36.113.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id D9CF918A85; Tue, 14 Apr 2020 14:49:27 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He References: <20200411093009.GH25745@shell.armlinux.org.uk> <20200412053507.GA4247@MiWiFi-R3L-srv> <20200412080836.GM25745@shell.armlinux.org.uk> <87wo6klbw0.fsf@x220.int.ebiederm.org> <20200413023701.GA20265@MiWiFi-R3L-srv> <871rorjzmc.fsf@x220.int.ebiederm.org> <20200414064031.GB4247@MiWiFi-R3L-srv> <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> <20200414092201.GD4247@MiWiFi-R3L-srv> <20200414143912.GE4247@MiWiFi-R3L-srv> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <0085f460-b0c7-b25f-36a7-fa3bafaab6fe@redhat.com> Date: Tue, 14 Apr 2020 16:49:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200414143912.GE4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: piliu@redhat.com, Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , "Eric W. Biederman" , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 14.04.20 16:39, Baoquan He wrote: > On 04/14/20 at 11:37am, David Hildenbrand wrote: >> On 14.04.20 11:22, Baoquan He wrote: >>> On 04/14/20 at 10:00am, David Hildenbrand wrote: >>>> On 14.04.20 08:40, Baoquan He wrote: >>>>> On 04/13/20 at 08:15am, Eric W. Biederman wrote: >>>>>> Baoquan He writes: >>>>>> >>>>>>> On 04/12/20 at 02:52pm, Eric W. Biederman wrote: >>>>>>>> >>>>>>>> The only benefit of kexec_file_load is that it is simple enough fr= om a >>>>>>>> kernel perspective that signatures can be checked. >>>>>>> >>>>>>> We don't have this restriction any more with below commit: >>>>>>> >>>>>>> commit 99d5cadfde2b ("kexec_file: split KEXEC_VERIFY_SIG into KEXEC= _SIG >>>>>>> and KEXEC_SIG_FORCE") >>>>>>> >>>>>>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover b= oth >>>>>>> secure boot or legacy system for kexec/kdump. Being simple enough i= s >>>>>>> enough to astract and convince us to use it instead. And kexec_file= _load >>>>>>> has been in use for several years on systems with secure boot, sinc= e >>>>>>> added in 2014, on x86_64. >>>>>> >>>>>> No. Actaully kexec_file_load is the less capable interface, and les= s >>>>>> flexible interface. Which is why it is appropriate for signature >>>>>> verification. >>>>> >>>>> Well, everyone has a stance and the corresponding view. You could hav= e >>>>> wider view from long time maintenance and in upstrem position, and th= ink >>>>> kexec_file_load is horrible. But I can only see from our work as a fr= ont >>>>> line engineer to maintain/develop kexec/kdump in RHEL, and think >>>>> kexec_file_load is easier to maintain. >>>>> >>>>> Surely except of multiple kernel image format support. No matter it i= s >>>>> kexec_load and kexec_file_load, e.g in x86_64, we only support bzImag= e. >>>>> This is produced from kerel building by default. We have no way to >>>>> support it in our distros and add it into kexec_file_load. >>>>> >>>>> [RFC PATCH] x86/boot: make ELF kernel multiboot-able >>>>> https://lkml.org/lkml/2017/2/15/654 >>>>> >>>>>> >>>>>>>> kexec_load in every other respect is the more capable and function= al >>>>>>>> interface. It makes no sense to get rid of it. >>>>>>>> >>>>>>>> It does make sense to reload with a loaded kernel on memory hotplu= g. >>>>>>>> That is simple and easy. If we are going to handle something in t= he >>>>>>>> kernel it should simple an automated unloading of the kernel on me= mory >>>>>>>> hotplug. >>>>>>>> >>>>>>>> >>>>>>>> I think it would be irresponsible to deprecate kexec_load on any >>>>>>>> platform. >>>>>>>> >>>>>>>> I also suspect that kexec_file_load could be taught to copy the dt= b >>>>>>>> on arm32 if someone wants to deal with signatures. >>>>>>>> >>>>>>>> We definitely can not even think of deprecating kexec_load until >>>>>>>> architecture that supports it also supports kexec_file_load and ev= eryone >>>>>>>> is happy with that interface. That is Linus's no regression rule. >>>>>>> >>>>>>> I should pick a milder word to express our tendency and tell our pl= an >>>>>>> then 'obsolete'. Even though I added 'gradually', seems it doesn't = help >>>>>>> much. I didn't mean to say 'deprecate' at all when replied. >>>>>>> >>>>>>> The situation and trend I understand about kexec_load and kexec_fil= e_load >>>>>>> are: >>>>>>> >>>>>>> 1) Supporting kexec_file_load is suggested to add in ARCHes which d= on't >>>>>>> have yet, just as x86_64, arm64 and s390 have done; >>>>>>> =20 >>>>>>> 2) kexec_file_load is suggested to use, and take precedence over >>>>>>> kexec_load in the future, if both are supported in one ARCH. >>>>>> >>>>>> The deep problem is that kexec_file_load is distinctly less expressi= ve >>>>>> than kexec_load. >>>>>> >>>>>>> 3) Kexec_load is kept being used by ARCHes w/o kexc_file_load suppo= rt, >>>>>>> and by ARCHes for back compatibility w/ kexec_file_load support. >>>>>>> >>>>>>> For 1) and 2), I think the reason is obvious as Eric said, >>>>>>> kexec_file_load is simple enough. And currently, whenever we got a = bug >>>>>>> report, we may need fix them twice, for kexec_load and kexec_file_l= oad. >>>>>>> If kexec_file_load is made by default, e.g on x86_64, we will chang= e it >>>>>>> in kernel space only, for kexec_file_load. This is what I meant abo= ut >>>>>>> 'obsolete gradually'. I think for arm64, s390, they will do these t= oo. >>>>>>> Unless there's some critical/blocker bug in kexec_load, to corrupt = the >>>>>>> old kexec_load interface in old product. >>>>>> >>>>>> Maybe. The code that kexec_file_load sucked into the kernel is quit= e >>>>>> stable and rarely needs changes except during a port of kexec to >>>>>> another architecture. >>>>>> >>>>>> Last I looked the real maintenance effor of kexec and kexec on panic= was >>>>>> in the drivers. So I don't think we can use maintenance to do anyth= ing. >>>>> >>>>> Not sure if I got it. But if check Lianbo's patches, a lot of effort = has >>>>> been taken to make SEV work well on kexec_file_load. And we have >>>>> switched to use kexec_file_load in the newly published Fedora releas= e >>>>> on x86_64 by default. Before this, Lianbo has investigated and done m= any >>>>> experiments to make sure the switching is safe. We finally made this >>>>> decision. Next we will do the switch in Enterprise distros. Once thes= e >>>>> are proved safe, we will suggest customers to use kexec_file_load for >>>>> kexec rebooting too. In the future, we will only care about >>>>> kexec_file_load if everying is going well. But as I have explained >>>>> repeatedly, only caring about kexec_file_load means we will leave >>>>> kexec_load as is, we will not add new feature or improvement patches >>>>> for it. >>>>> >>>>> commit 6a20bd54473e11011bf2b47efb52d0759d412854 >>>>> Author: Lianbo Jiang >>>>> Date: Thu Jan 16 13:47:35 2020 +0800 >>>>> >>>>> kdump-lib: switch to the kexec_file_load() syscall on x86_64 by d= efault >>>>> >>>>>> >>>>>>> For 3), people can still use kexec_load and develop/fix for it, if = no >>>>>>> kexec_file_load supported. But 32-bit arm should be a different one= , >>>>>>> more like i386, we will leave it as is, and fix anything which coul= d >>>>>>> break it. But people really expects to improve or add feature to it= ? E.g >>>>>>> in this patchset, the mem hotplug issue James raised, I assume Jame= s is >>>>>>> focusing on arm64, x86_64, but not 32-bit arm. As DavidH commented = in >>>>>>> another reply, people even don't agree to continue supporting memor= y >>>>>>> hotplug on 32-bit system. We ever took effort to fix a memory hotpl= ug >>>>>>> bug on i386 with a patch, but people would rather set it as BROKEN. >>>>>> >>>>>> For memory hotplug just reload. Userspace already gets good events. >>>>> >>>>> Kexec_file_load is easy to maintain. This is an example. >>>>> >>>>> Lock the hotplug area where kexed-ed kernel is targeted in this patch= set, >>>>> it's obviously not right. We can't disable memory hotplug just becaus= e >>>>> kexec-ed kernel is loaded ahead of time.=20 >>>>> >>>>> Reloading is also not a good fix. Kexec-ed kernel is targeted at a >>>>> movable area, reloading can avoid kexec rebooting corruption if that >>>>> area is hot removed. But if that area is not removed, locating kernel >>>>> into the hotpluggable area will change the area into ummovable zone. >>>>> Unless we decide to not support memory hotplug in kexec-ed kernel, I >>>>> guess it's very hard. Now in our distros kexec rebooting has been >>>>> supported, the big cloud providers are deploying linux in guest, bugs= on >>>>> kexec reboot failure has been reported. They need the memory hotplug = to >>>>> increase/decrease memory. >>>>> >>>>> The root cause is kexec-ed kernel is targeted at hotpluggable memory >>>>> region. Just avoiding the movable area can fix it. In kexec_file_load= (), >>>>> just checking or picking those unmovable region to put kernel/initrd = in >>>>> function locate_mem_hole_callback() can fix it. The page or pageblock= 's >>>>> zone is movable or not, it's easy to know. This fix doesn't need to >>>>> bother other component. >>>> >>>> I don't fully agree. E.g., just because memory is onlined to ZONE_NORM= AL >>>> does not imply that it cannot get offlined and removed e.g., this is >>>> heavily used on ppc64, with 16MB sections. >>> >>> Really? I just know there are two kinds of mem hoplug in ppc, but don't >>> know the details. So in this case, is there any flag or a way to know >>> those memory block are hotpluggable? I am curious how those kernel data >>> is avoided to be put in this area. Or ppc just freely uses it for kerne= l >>> data or user space data, then try to migrate when hot remove? >> >> See >> arch/powerpc/platforms/pseries/hotplug-memory.c:dlpar_memory_remove_by_c= ount() >> >> Under DLAPR, it can remove memory in LMB granularity, which is usually >> 16MB (=3D=3D single section on ppc64). DLPAR will directly online all >> hotplugged memory (LMBs) from the kernel using device_online(), which >> will go to ZONE_NORMAL. >> >> When trying to remove memory, it simply scans for offlineable 16MB >> memory blocks (=3D=3Dsection =3D=3D LMB), offlines and removes them. No = need for >> the movable zone and all the involved issues. >=20 > Yes, this is a different one, thanks for pointing it out. It sounds like > balloon driver in virt platform, doesn't it? With DLPAR there is a hypervisor involved (which manages the actual HW DIMMs), so yes. >=20 > Avoiding to put kexec kernel into movable zone can't solve this DLPAR > case as you said. >=20 >> >> Now, the interesting question is, can we have LMBs added during boot >> (not via add_memory()), that will later be removed via remove_memory(). >> IIRC, we had BUGs related to that, so I think yes. If a section contains >> no unmovable allocations (after boot), it can get removed. >=20 > I do want to ask this question. If we can add LMB into system RAM, then > reload kexec can solve it.=20 >=20 > Another better way is adding a common function to filter out the > movable zone when search position for kexec kernel, use a arch specific > funciton to filter out DLPAR memory blocks for ppc only. Over there, > we can simply use for_each_drmem_lmb() to do that. I was thinking about something similar. Maybe something like a notifier that can be used to test if selected memory can be used for kexec images. It would apply to - arm64 and filter out all hotadded memory (IIRC, only boot memory can be used). - 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(). --=20 Thanks, David / dhildenb