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[91.12.99.11]) by smtp.gmail.com with ESMTPSA id l5sm5967522wrc.90.2021.08.05.01.07.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Aug 2021 01:07:21 -0700 (PDT) To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20210730085249.8246-1-david@redhat.com> <20210730085249.8246-7-david@redhat.com> <5f8c6173-046d-9fc2-c649-93ede45ca77d@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v3 6/7] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination Message-ID: Date: Thu, 5 Aug 2021 10:07:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <5f8c6173-046d-9fc2-c649-93ede45ca77d@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.132, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Alex Williamson , Eduardo Habkost , Juan Quintela , "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , Peter Xu , Andrey Gruzdev , Pankaj Gupta , teawater , Paolo Bonzini , Marek Kedzierski , Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05.08.21 09:48, Philippe Mathieu-Daudé wrote: > On 7/30/21 10:52 AM, David Hildenbrand wrote: >> Currently, when someone (i.e., the VM) accesses discarded parts inside a >> RAMBlock with a RamDiscardManager managing the corresponding mapped memory >> region, postcopy will request migration of the corresponding page from the >> source. The source, however, will never answer, because it refuses to >> migrate such pages with undefined content ("logically unplugged"): the >> pages are never dirty, and get_queued_page() will consequently skip >> processing these postcopy requests. >> >> Especially reading discarded ("logically unplugged") ranges is supposed to >> work in some setups (for example with current virtio-mem), although it >> barely ever happens: still, not placing a page would currently stall the >> VM, as it cannot make forward progress. >> >> Let's check the state via the RamDiscardManager (the state e.g., >> of virtio-mem is migrated during precopy) and avoid sending a request >> that will never get answered. Place a fresh zero page instead to keep >> the VM working. This is the same behavior that would happen >> automatically without userfaultfd being active, when accessing virtual >> memory regions without populated pages -- "populate on demand". >> >> For now, there are valid cases (as documented in the virtio-mem spec) where >> a VM might read discarded memory; in the future, we will disallow that. >> Then, we might want to handle that case differently, e.g., warning the >> user that the VM seems to be mis-behaving. >> >> Signed-off-by: David Hildenbrand >> --- >> migration/postcopy-ram.c | 31 +++++++++++++++++++++++++++---- >> migration/ram.c | 21 +++++++++++++++++++++ >> migration/ram.h | 1 + >> 3 files changed, 49 insertions(+), 4 deletions(-) >> >> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c >> index 2e9697bdd2..38cdfc09c3 100644 >> --- a/migration/postcopy-ram.c >> +++ b/migration/postcopy-ram.c >> @@ -671,6 +671,29 @@ int postcopy_wake_shared(struct PostCopyFD *pcfd, >> return ret; >> } >> >> +static int postcopy_request_page(MigrationIncomingState *mis, RAMBlock *rb, >> + ram_addr_t start, uint64_t haddr) >> +{ >> + void *aligned = (void *)(uintptr_t)(haddr & -qemu_ram_pagesize(rb)); > > void *aligned = QEMU_ALIGN_PTR_DOWN(haddr, qemu_ram_pagesize(rb))); > Does not compile as haddr is not a pointer. void *aligned = QEMU_ALIGN_PTR_DOWN((void *)haddr, qemu_ram_pagesize(rb))); should work. I can also add a patch to adjust a similar call in migrate_send_rp_req_pages()! Thanks! -- Thanks, David / dhildenb