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Fri, 21 Feb 2020 08:41:43 +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 5C5AB90F79; Fri, 21 Feb 2020 08:41:35 +0000 (UTC) Subject: Re: [PATCH v1 10/13] migrate/ram: Handle RAM block resizes during postcopy From: David Hildenbrand To: Peter Xu References: <20200219161725.115218-1-david@redhat.com> <20200219161725.115218-11-david@redhat.com> <20200220205443.GD15253@xz-x1> <9a4207fe-4b35-8b6a-6b29-3ad2e704b492@redhat.com> 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: <0bef755a-a798-5cca-ef5d-d1df7affa07c@redhat.com> Date: Fri, 21 Feb 2020 09:41:34 +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: <9a4207fe-4b35-8b6a-6b29-3ad2e704b492@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: HJRojBDcMm2LQKu9mvb25Q-1 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: 207.211.31.81 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 09:35, David Hildenbrand wrote: > On 20.02.20 21:54, Peter Xu wrote: >> On Wed, Feb 19, 2020 at 05:17:22PM +0100, 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 d= oes >>> not expect this to change at random points in time. >>> >>> In the case of postcopy, relying on used_length is racy as soon as the >>> guest is running. Also, when used_length changes we might leave the >>> uffd handler registered for some memory regions, reject valid pages >>> when migrating and fail when sending the recv bitmap to 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() >>> >>> Let's remember the original used_length in a separate variable and >>> use it in relevant postcopy code. Make sure to update it when we resize >>> during precopy, when synchronizing the RAM block sizes with the source. >>> >>> 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 >>> --- >>> include/exec/ramblock.h | 9 +++++++++ >>> migration/postcopy-ram.c | 15 ++++++++++++--- >>> migration/ram.c | 11 +++++++++-- >>> 3 files changed, 30 insertions(+), 5 deletions(-) >>> >>> diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h >>> index 07d50864d8..0e9e9b346b 100644 >>> --- a/include/exec/ramblock.h >>> +++ b/include/exec/ramblock.h >>> @@ -59,6 +59,15 @@ struct RAMBlock { >>> */ >>> unsigned long *clear_bmap; >>> uint8_t clear_bmap_shift; >>> + >>> + /* >>> + * RAM block used_length before the guest started running while po= stcopy >>> + * was active. Once the guest is running, used_length can change. = Used to >>> + * register/unregister uffd handlers and as the size of the recv b= itmap. >>> + * Receiving any page beyond this length will bail out, as it coul= d not have >>> + * been valid on the source. >>> + */ >>> + ram_addr_t postcopy_length; >>> }; >>> #endif >>> #endif >>> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c >>> index a36402722b..c68caf4e42 100644 >>> --- a/migration/postcopy-ram.c >>> +++ b/migration/postcopy-ram.c >>> @@ -17,6 +17,7 @@ >>> */ >>> =20 >>> #include "qemu/osdep.h" >>> +#include "qemu/rcu.h" >>> #include "exec/target_page.h" >>> #include "migration.h" >>> #include "qemu-file.h" >>> @@ -31,6 +32,7 @@ >>> #include "qemu/error-report.h" >>> #include "trace.h" >>> #include "hw/boards.h" >>> +#include "exec/ramblock.h" >>> =20 >>> /* Arbitrary limit on size of each discard command, >>> * keeps them around ~200 bytes >>> @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) >>> ram_addr_t length =3D qemu_ram_get_used_length(rb); >>> trace_postcopy_init_range(block_name, host_addr, offset, length); >>> =20 >>> + /* >>> + * Save the used_length before running the guest. In case we have = to >>> + * resize RAM blocks when syncing RAM block sizes from the source = during >>> + * precopy, we'll update it manually via the ram block notifier. >>> + */ >>> + rb->postcopy_length =3D length; >>> + >>> /* >>> * We need the whole of RAM to be truly empty for postcopy, so thi= ngs >>> * like ROMs and any data tables built during init must be zero'd >>> @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque= ) >>> const char *block_name =3D qemu_ram_get_idstr(rb); >>> void *host_addr =3D qemu_ram_get_host_addr(rb); >>> ram_addr_t offset =3D qemu_ram_get_offset(rb); >>> - ram_addr_t length =3D qemu_ram_get_used_length(rb); >>> + ram_addr_t length =3D rb->postcopy_length; >>> MigrationIncomingState *mis =3D opaque; >>> struct uffdio_range range_struct; >>> trace_postcopy_cleanup_range(block_name, host_addr, offset, length= ); >>> @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) >>> const char *block_name =3D qemu_ram_get_idstr(rb); >>> void *host_addr =3D qemu_ram_get_host_addr(rb); >>> ram_addr_t offset =3D qemu_ram_get_offset(rb); >>> - ram_addr_t length =3D qemu_ram_get_used_length(rb); >>> + ram_addr_t length =3D rb->postcopy_length; >>> trace_postcopy_nhp_range(block_name, host_addr, offset, length); >>> =20 >>> /* >>> @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, vo= id *opaque) >>> struct uffdio_register reg_struct; >>> =20 >>> reg_struct.range.start =3D (uintptr_t)qemu_ram_get_host_addr(rb); >>> - reg_struct.range.len =3D qemu_ram_get_used_length(rb); >>> + reg_struct.range.len =3D rb->postcopy_length; >>> reg_struct.mode =3D UFFDIO_REGISTER_MODE_MISSING; >>> =20 >>> /* Now tell our userfault_fd that it's responsible for this area *= / >>> diff --git a/migration/ram.c b/migration/ram.c >>> index ab1f5534cf..6d1dcb362c 100644 >>> --- a/migration/ram.c >>> +++ b/migration/ram.c >>> @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, >>> return -1; >>> } >>> =20 >>> - nbits =3D block->used_length >> TARGET_PAGE_BITS; >>> + nbits =3D block->postcopy_length >> TARGET_PAGE_BITS; >>> =20 >>> /* >>> * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit >>> @@ -3159,7 +3159,13 @@ static int ram_load_postcopy(QEMUFile *f) >>> break; >>> } >>> =20 >>> - if (!offset_in_ramblock(block, addr)) { >>> + /* >>> + * Relying on used_length is racy and can result in false = positives. >>> + * We might place pages beyond used_length in case RAM was= shrunk >>> + * while in postcopy, which is fine - trying to place via >>> + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. >>> + */ >>> + if (!block->host || addr >=3D block->postcopy_length) { >>> error_report("Illegal RAM offset " RAM_ADDR_FMT, addr)= ; >>> ret =3D -EINVAL; >>> break; >>> @@ -3744,6 +3750,7 @@ static void ram_mig_ram_block_resized(RAMBlockNot= ifier *n, void *host, >>> rb->idstr); >>> } >>> } >>> + rb->postcopy_length =3D new_size; >> >> With this change, postcopy_length will be the same as used_length? >> >> I thought you wanted to cache that value when starting the postcopy >> phase so postcopy_length should be constant after set once. Did I >> misunderstood? >=20 > So, my understanding on the migration target: >=20 > 1. Source VM started and initialized. "Destination VM", sorry. --=20 Thanks, David / dhildenb