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Fri, 21 Feb 2020 10:20:09 +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 975BD19756; Fri, 21 Feb 2020 10:19:59 +0000 (UTC) Subject: Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy From: David Hildenbrand To: Peter Xu References: <20200219161725.115218-1-david@redhat.com> <20200219161725.115218-6-david@redhat.com> <3c3d4d50-a30d-b4e9-6256-4656f4e78cf6@redhat.com> <20200220201719.GC15253@xz-x1> 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: <81ca5783-97d5-555c-c361-9b5b0ec144b3@redhat.com> Date: Fri, 21 Feb 2020 11:19:58 +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: 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] X-Received-From: 205.139.110.61 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, "Dr . David Alan Gilbert" , 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 11:10, David Hildenbrand wrote: > On 21.02.20 10:18, David Hildenbrand wrote: >> On 20.02.20 21:17, Peter Xu wrote: >>> On Thu, Feb 20, 2020 at 04:16:02PM +0100, David Hildenbrand wrote: >>>> On 19.02.20 17:17, David Hildenbrand 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 sou= rce, >>>>> after syncing the RAM block list in ram_save_setup(), so as long as t= he >>>>> 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 simpl= y >>>>> cancel migration and indicate the reason. We'll continue running on t= he >>>>> 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 ca= nceled. >>>>> + * 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 d= etect >>>>> 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 migrate= d. >>>>> - * This used_length size can change across reboots. >>>>> + * Resizing RAM while migrating can result in the migration being ca= nceled. >>>>> */ >>>>> #define RAM_RESIZEABLE (1 << 2) >>>>> =20 >>>>> @@ -843,7 +843,9 @@ void memory_region_init_ram_shared_nomigrate(Memo= ryRegion *mr, >>>>> * RAM. Accesses into the regio= n will >>>>> * modify memory directly. Only= an initial >>>>> * portion of this RAM is actual= ly used. >>>>> - * The used size can change acro= ss reboots. >>>>> + * Changing the size while migra= ting >>>>> + * can result in the migration b= eing >>>>> + * 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 *m= r); >>>>> =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 ca= nceled. >>>>> + * Care has to be taken if the guest might have already detected the= memory. >>>>> * >>>>> * @mr: a memory region created with @memory_region_init_resizeable_= ram. >>>>> * @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 fu= nc, 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 *hos= t, >>>>> + size_t old_size, size_t new_si= ze) >>>>> +{ >>>>> + 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 re= sizes, >>>>> + * as we only care about resizes during precopy on the migration= source. >>>>> + * This handler is always registered, so ignore when migration i= s idle. >>>>> + */ >>>>> + if (migration_is_idle() || !runstate_is_running() || >>> >>> So I noticed that I mis-misread the code after chat with Dave... >>> >>> migration_is_idle() should only return false if on the source and only >>> if during migration. Destination should still return true for that >>> (destination VM reads state from MigrationIncomingState.state >>> instead). >>> >>> With that, I think we can drop the confusing !runstate_is_running() >>> check because migration_is_idle() will cover that (and touch up the >>> comment too)? >> >> So, we want to cancel migration whenever we are on the source and we are >> migrating (postcopy). Resizing will only happen while the VM is running >> on the source once we're migrating. >> >> So you're saying that >> >> if (migration_is_idle() || postcopy_is_running()) { >> =09return: >> } >> >> is enough. Will migration_is_idle() always return true on the >> destination (I remember something different, but might be *I* misread >> the code)? >> >> Then this would distill down to >> >> if (migration_is_idle()) { >> =09return: >> } >> >> Which would be nice. >=20 > ... but looking at process_incoming_migration_co(), we'll set the state > to MIGRATION_STATUS_ACTIVE right at the start. >=20 >=20 > So dropping postcopy_is_running() would be wrong and dropping > !runstate_is_running() would be wrong as well right now. >=20 > What we actually want is >=20 > if (!migration_outgoing()) { > =09return; > } >=20 > Any experts? >=20 Lol, man this code is confusing. So, migration_is_idle() really only checks current_migration, not current_incoming. I didn't expect to be knees deep in migration code at this point ... if (migration_is_idle()) { =09return: } works. Thanks! --=20 Thanks, David / dhildenb