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Mon, 24 Feb 2020 14:26:20 -0800 (PST) Date: Mon, 24 Feb 2020 17:26:18 -0500 From: Peter Xu To: David Hildenbrand Subject: Re: [PATCH v2 10/13] migration/ram: Handle RAM block resizes during postcopy Message-ID: <20200224222618.GA113102@xz-x1> References: <20200221164204.105570-1-david@redhat.com> <20200221164204.105570-11-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200221164204.105570-11-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline 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 , Alex =?utf-8?Q?Benn=C3=A9e?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Feb 21, 2020 at 05:42:01PM +0100, David Hildenbrand wrote: [...] > @@ -3160,7 +3160,13 @@ 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 po= sitives. > + * We might place pages beyond used_length in case RAM was s= hrunk > + * 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) { I'm thinking whether we can even avoid the -ENOENT failure of UFFDIO_COPY. With the postcopy_length you introduced, I think it's the case when addr >=3D used_length && addr < postcopy_length, right? Can we skip those? Thanks, > error_report("Illegal RAM offset " RAM_ADDR_FMT, addr); > ret =3D -EINVAL; > break; > @@ -3757,6 +3763,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotif= ier *n, void *host, > rb->idstr); > } > } > + rb->postcopy_length =3D new_size; > break; > case POSTCOPY_INCOMING_NONE: > case POSTCOPY_INCOMING_RUNNING: > --=20 > 2.24.1 >=20 --=20 Peter Xu