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Fri, 21 Feb 2020 15:46:13 +0000 (UTC) Received: from [10.36.117.197] (ovpn-117-197.ams2.redhat.com [10.36.117.197]) by smtp.corp.redhat.com (Postfix) with ESMTP id 235E227090; Fri, 21 Feb 2020 15:46:05 +0000 (UTC) Subject: Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy To: "Dr. David Alan Gilbert" References: <20200219161725.115218-1-david@redhat.com> <20200219161725.115218-6-david@redhat.com> <20200221151447.GF2931@work-vm> <20200221154017.GG2931@work-vm> 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: Date: Fri, 21 Feb 2020 16:46:05 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200221154017.GG2931@work-vm> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , Juan Quintela , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, Peter Xu , Shannon Zhao , Igor Mammedov , Paolo Bonzini , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 21.02.20 16:40, Dr. David Alan Gilbert wrote: > * David Hildenbrand (david@redhat.com) wrote: >> On 21.02.20 16:14, Dr. David Alan Gilbert wrote: >>> * David Hildenbrand (david@redhat.com) wrote: >>>> Resizing while migrating is dangerous and does not work as expected. >>>> The whole migration code works on the usable_length of ram blocks and = does >>>> not expect this to change at random points in time. >>>> >>>> In the case of precopy, the ram block size must not change on the sour= ce, >>>> after syncing the RAM block list in ram_save_setup(), so as long as th= e >>>> guest is still running on the source. >>>> >>>> Resizing can be trigger *after* (but not during) a reset in >>>> ACPI code by the guest >>>> - hw/arm/virt-acpi-build.c:acpi_ram_update() >>>> - hw/i386/acpi-build.c:acpi_ram_update() >>>> >>>> Use the ram block notifier to get notified about resizes. Let's simply >>>> cancel migration and indicate the reason. We'll continue running on th= e >>>> source. No harm done. >>>> >>>> Update the documentation. Postcopy will be handled separately. >>>> >>>> Cc: "Dr. David Alan Gilbert" >>>> Cc: Juan Quintela >>>> Cc: Eduardo Habkost >>>> Cc: Paolo Bonzini >>>> Cc: Igor Mammedov >>>> Cc: "Michael S. Tsirkin" >>>> Cc: Richard Henderson >>>> Cc: Shannon Zhao >>>> Cc: Alex Benn=C3=A9e >>>> Cc: Peter Xu >>>> Signed-off-by: David Hildenbrand >>>> --- >>>> exec.c | 5 +++-- >>>> include/exec/memory.h | 10 ++++++---- >>>> migration/migration.c | 9 +++++++-- >>>> migration/migration.h | 1 + >>>> migration/ram.c | 41 +++++++++++++++++++++++++++++++++++++++++ >>>> 5 files changed, 58 insertions(+), 8 deletions(-) >>>> >>>> diff --git a/exec.c b/exec.c >>>> index b75250e773..8b015821d6 100644 >>>> --- a/exec.c >>>> +++ b/exec.c >>>> @@ -2120,8 +2120,9 @@ static int memory_try_enable_merging(void *addr,= size_t len) >>>> return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE); >>>> } >>>> =20 >>>> -/* Only legal before guest might have detected the memory size: e.g. = on >>>> - * incoming migration, or right after reset. >>>> +/* >>>> + * Resizing RAM while migrating can result in the migration being can= celed. >>>> + * Care has to be taken if the guest might have already detected the = memory. >>>> * >>>> * As memory core doesn't know how is memory accessed, it is up to >>>> * resize callback to update device state and/or add assertions to de= tect >>>> diff --git a/include/exec/memory.h b/include/exec/memory.h >>>> index e85b7de99a..de111347e8 100644 >>>> --- a/include/exec/memory.h >>>> +++ b/include/exec/memory.h >>>> @@ -113,7 +113,7 @@ typedef struct IOMMUNotifier IOMMUNotifier; >>>> #define RAM_SHARED (1 << 1) >>>> =20 >>>> /* Only a portion of RAM (used_length) is actually used, and migrated= . >>>> - * This used_length size can change across reboots. >>>> + * Resizing RAM while migrating can result in the migration being can= celed. >>>> */ >>>> #define RAM_RESIZEABLE (1 << 2) >>>> =20 >>>> @@ -843,7 +843,9 @@ void memory_region_init_ram_shared_nomigrate(Memor= yRegion *mr, >>>> * RAM. Accesses into the region= will >>>> * modify memory directly. Only = an initial >>>> * portion of this RAM is actuall= y used. >>>> - * The used size can change acros= s reboots. >>>> + * Changing the size while migrat= ing >>>> + * can result in the migration be= ing >>>> + * canceled. >>>> * >>>> * @mr: the #MemoryRegion to be initialized. >>>> * @owner: the object that tracks the region's reference count >>>> @@ -1464,8 +1466,8 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr= ); >>>> =20 >>>> /* memory_region_ram_resize: Resize a RAM region. >>>> * >>>> - * Only legal before guest might have detected the memory size: e.g. = on >>>> - * incoming migration, or right after reset. >>>> + * Resizing RAM while migrating can result in the migration being can= celed. >>>> + * Care has to be taken if the guest might have already detected the = memory. >>>> * >>>> * @mr: a memory region created with @memory_region_init_resizeable_r= am. >>>> * @newsize: the new size the region >>>> diff --git a/migration/migration.c b/migration/migration.c >>>> index 8fb68795dc..ac9751dbe5 100644 >>>> --- a/migration/migration.c >>>> +++ b/migration/migration.c >>>> @@ -175,13 +175,18 @@ void migration_object_init(void) >>>> } >>>> } >>>> =20 >>>> +void migration_cancel(void) >>>> +{ >>>> + migrate_fd_cancel(current_migration); >>>> +} >>>> + >>>> void migration_shutdown(void) >>>> { >>>> /* >>>> * Cancel the current migration - that will (eventually) >>>> * stop the migration using this structure >>>> */ >>>> - migrate_fd_cancel(current_migration); >>>> + migration_cancel(); >>>> object_unref(OBJECT(current_migration)); >>>> } >>>> =20 >>>> @@ -2019,7 +2024,7 @@ void qmp_migrate(const char *uri, bool has_blk, = bool blk, >>>> =20 >>>> void qmp_migrate_cancel(Error **errp) >>>> { >>>> - migrate_fd_cancel(migrate_get_current()); >>>> + migration_cancel(); >>>> } >>>> =20 >>>> void qmp_migrate_continue(MigrationStatus state, Error **errp) >>>> diff --git a/migration/migration.h b/migration/migration.h >>>> index 8473ddfc88..79fd74afa5 100644 >>>> --- a/migration/migration.h >>>> +++ b/migration/migration.h >>>> @@ -343,5 +343,6 @@ int foreach_not_ignored_block(RAMBlockIterFunc fun= c, void *opaque); >>>> void migration_make_urgent_request(void); >>>> void migration_consume_urgent_request(void); >>>> bool migration_rate_limit(void); >>>> +void migration_cancel(void); >>>> =20 >>>> #endif >>>> diff --git a/migration/ram.c b/migration/ram.c >>>> index ed23ed1c7c..57f32011a3 100644 >>>> --- a/migration/ram.c >>>> +++ b/migration/ram.c >>>> @@ -52,6 +52,7 @@ >>>> #include "migration/colo.h" >>>> #include "block.h" >>>> #include "sysemu/sysemu.h" >>>> +#include "sysemu/runstate.h" >>>> #include "savevm.h" >>>> #include "qemu/iov.h" >>>> #include "multifd.h" >>>> @@ -3710,8 +3711,48 @@ static SaveVMHandlers savevm_ram_handlers =3D { >>>> .resume_prepare =3D ram_resume_prepare, >>>> }; >>>> =20 >>>> +static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host= , >>>> + size_t old_size, size_t new_siz= e) >>>> +{ >>>> + ram_addr_t offset; >>>> + Error *err =3D NULL; >>>> + RAMBlock *rb =3D qemu_ram_block_from_host(host, false, &offset); >>>> + >>>> + if (ramblock_is_ignored(rb)) { >>>> + return; >>>> + } >>>> + >>>> + /* >>>> + * Some resizes are triggered on the migration target by precopy = code, >>>> + * when synchronizing RAM block sizes. In these cases, the VM is = not >>>> + * running and migration is not idle. We have to ignore these res= izes, >>>> + * as we only care about resizes during precopy on the migration = source. >>>> + * This handler is always registered, so ignore when migration is= idle. >>>> + */ >>>> + if (migration_is_idle() || !runstate_is_running() || >>>> + postcopy_is_running()) { >>>> + return; >>>> + } >>>> + >>>> + /* >>>> + * Precopy code cannot deal with the size of ram blocks changing = at >>>> + * random points in time. We're still running on the source, abor= t >>>> + * the migration and continue running here. Make sure to wait unt= il >>>> + * migration was canceled. >>>> + */ >>>> + error_setg(&err, "RAM block '%s' resized during precopy.", rb->id= str); >>>> + migrate_set_error(migrate_get_current(), err); >>>> + error_free(err); >>>> + migration_cancel(); >>>> +} >>>> + >>>> +static RAMBlockNotifier ram_mig_ram_notifier =3D { >>>> + .ram_block_resized =3D ram_mig_ram_block_resized, >>>> +}; >>>> + >>>> void ram_mig_init(void) >>>> { >>>> qemu_mutex_init(&XBZRLE.lock); >>>> register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_stat= e); >>>> + ram_block_notifier_add(&ram_mig_ram_notifier); >>> >>> Can we avoid the question of the 'is_idle' checks by doing this >>> registration in save_setup/load_setup and unregistering in >>> save_cleanup/load_cleanup? >> >> Well, I figured it out now :) >> >> migration_is_idle() is enough to handle it in this patch. >> >>> >>> That means if we land in the handler we know we're in either an incomin= g >>> or outgoing migration and then you just have to check which? >> >> Can save/load race with other QEMU code that might register/unregister >> notifiers? I want to avoid having to introduce locking just for that. >=20 > It looks like it can; qemu_savevm_state_setup > is called from near the top of migration_thread, so I don't > think it's holding locks at that point; and all the existing notifier > changes on this notifier seem to be done from either init or vfio_open > which I guess is under the big lock (?) Yes, same as actual resizes AFAIK (which could otherwise also race with (un)registration when traversing the list). So I'd prefer to not register the notifier dynamically for now. (at least makes it easier for me :) ) --=20 Thanks, David / dhildenb