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([2001:b07:6468:f312:a0d1:fc42:c610:f977]) by smtp.gmail.com with ESMTPSA id f131sm29355950wme.40.2020.08.17.09.27.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Aug 2020 09:27:19 -0700 (PDT) Subject: Re: [PATCH] memory: Directly dispatch alias accesses on origin memory region To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200816173051.16274-1-f4bug@amsat.org> From: Paolo Bonzini Message-ID: <706c1969-3e73-7a8e-d4fe-9a2516f44054@redhat.com> Date: Mon, 17 Aug 2020 18:27:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200816173051.16274-1-f4bug@amsat.org> Content-Language: en-US Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/17 03:34:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, 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: Peter Maydell , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 16/08/20 19:30, Philippe Mathieu-Daudé wrote: > There is an issue when accessing an alias memory region via the > memory_region_dispatch_read() / memory_region_dispatch_write() > calls: > > The memory_region_init_alias() flow is: > > memory_region_init_alias() > -> memory_region_init() > -> object_initialize(TYPE_MEMORY_REGION) > -> memory_region_initfn() > -> mr->ops = &unassigned_mem_ops; > > Later when accessing the alias, the memory_region_dispatch_read() > flow is: > > memory_region_dispatch_read() > -> memory_region_access_valid(mr) > -> mr->ops->valid.accepts() > -> unassigned_mem_accepts() > <- false > <- false > <- MEMTX_DECODE_ERROR > > The caller gets a MEMTX_DECODE_ERROR while the access is OK. What is the path that leads to this call? > Fix by directly dispatching aliases accesses to its origin region. > > Fixes: 2cdfcf272d ("memory: assign MemoryRegionOps to all regions") I don't think the "Fixes" is okay because you'd have gotten a different bug before. > + if (mr->alias) { > + addr += mr->alias_offset; > + mr = mr->alias; > + } Also, I think this would have to be a while loop. Paolo