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[79.242.60.54]) by smtp.gmail.com with ESMTPSA id y19sm2606311wma.21.2021.07.27.05.41.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Jul 2021 05:41:17 -0700 (PDT) Subject: Re: [PATCH v2 0/9] memory: Sanity checks memory transaction when releasing BQL To: Peter Xu , qemu-devel@nongnu.org References: <20210723193444.133412-1-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: <7f056d75-51a1-17a8-e946-1aeccb3e1308@redhat.com> Date: Tue, 27 Jul 2021 14:41:17 +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: <20210723193444.133412-1-peterx@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: 7bit 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: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.717, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.438, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 23.07.21 21:34, Peter Xu wrote: > This is v2 of the series. It was actually got forgotten for months until it > was used to identify another potential issue of bql usage here (besides it > could still be helpful when debugging a previous kvm dirty ring issue in that > series): > > https://lore.kernel.org/qemu-devel/CH0PR02MB7898BBD73D0F3F7D5003BB178BE19@CH0PR02MB7898.namprd02.prod.outlook.com/ > > So I figured maybe it's still worth to have it, hence a repost. > > There're some changes against v1: > > - patch "cpus: Introduce qemu_cond_timedwait_iothread()" is dropped because > it's introduced in another commit already (b0c3cf9407e64). > > - two more patches to move do_run_on_cpu() into softmmu/ to fix a linux-user > compliation issue. > > Please review, thanks. > > === Original Cover letter === > > This is a continuous work of previous discussion on memory transactions [1]. > It should be helpful to fail QEMU far earlier if there's misuse of BQL against > the QEMU memory model. > > One example is run_on_cpu() during memory commit. That'll work previously, but > it'll fail with very strange errors (like KVM ioctl failure due to memslot > already existed, and it's not guaranteed to trigger constantly). Now it'll > directly fail when run_on_cpu() is called. > Functions that silently drop the BQL are really nasty. I once fall into a similar trap calling pause_all_vcpus() from within memory_region_transaction_begin(), while resizing RAM blocks. -- Thanks, David / dhildenb