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[83.59.160.93]) by smtp.gmail.com with ESMTPSA id e17sm118776eja.51.2020.06.17.07.42.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Jun 2020 07:42:53 -0700 (PDT) Subject: Re: [PATCH 0/6] Add various undefined MMIO r/w functions To: =?UTF-8?Q?Alex_Benn=c3=a9e?= References: <20200617053934.122642-1-ppandit@redhat.com> <20200617063956.GA12597@umbus.fritz.box> <20200617070621.29051d4b@x1.home> <8357f8a5-83e3-47a7-57c9-b88edfa3812c@redhat.com> <87tuz9wzwq.fsf@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Autocrypt: addr=philmd@redhat.com; keydata= mQINBDXML8YBEADXCtUkDBKQvNsQA7sDpw6YLE/1tKHwm24A1au9Hfy/OFmkpzo+MD+dYc+7 bvnqWAeGweq2SDq8zbzFZ1gJBd6+e5v1a/UrTxvwBk51yEkadrpRbi+r2bDpTJwXc/uEtYAB GvsTZMtiQVA4kRID1KCdgLa3zztPLCj5H1VZhqZsiGvXa/nMIlhvacRXdbgllPPJ72cLUkXf z1Zu4AkEKpccZaJspmLWGSzGu6UTZ7UfVeR2Hcc2KI9oZB1qthmZ1+PZyGZ/Dy+z+zklC0xl XIpQPmnfy9+/1hj1LzJ+pe3HzEodtlVA+rdttSvA6nmHKIt8Ul6b/h1DFTmUT1lN1WbAGxmg CH1O26cz5nTrzdjoqC/b8PpZiT0kO5MKKgiu5S4PRIxW2+RA4H9nq7nztNZ1Y39bDpzwE5Sp bDHzd5owmLxMLZAINtCtQuRbSOcMjZlg4zohA9TQP9krGIk+qTR+H4CV22sWldSkVtsoTaA2 qNeSJhfHQY0TyQvFbqRsSNIe2gTDzzEQ8itsmdHHE/yzhcCVvlUzXhAT6pIN0OT+cdsTTfif MIcDboys92auTuJ7U+4jWF1+WUaJ8gDL69ThAsu7mGDBbm80P3vvUZ4fQM14NkxOnuGRrJxO qjWNJ2ZUxgyHAh5TCxMLKWZoL5hpnvx3dF3Ti9HW2dsUUWICSQARAQABtDJQaGlsaXBwZSBN YXRoaWV1LURhdWTDqSAoUGhpbCkgPHBoaWxtZEByZWRoYXQuY29tPokCVQQTAQgAPwIbDwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AWIQSJweePYB7obIZ0lcuio/1u3q3A3gUCXsfWwAUJ KtymWgAKCRCio/1u3q3A3ircD/9Vjh3aFNJ3uF3hddeoFg1H038wZr/xi8/rX27M1Vj2j9VH 0B8Olp4KUQw/hyO6kUxqkoojmzRpmzvlpZ0cUiZJo2bQIWnvScyHxFCv33kHe+YEIqoJlaQc JfKYlbCoubz+02E2A6bFD9+BvCY0LBbEj5POwyKGiDMjHKCGuzSuDRbCn0Mz4kCa7nFMF5Jv piC+JemRdiBd6102ThqgIsyGEBXuf1sy0QIVyXgaqr9O2b/0VoXpQId7yY7OJuYYxs7kQoXI 6WzSMpmuXGkmfxOgbc/L6YbzB0JOriX0iRClxu4dEUg8Bs2pNnr6huY2Ft+qb41RzCJvvMyu gS32LfN0bTZ6Qm2A8ayMtUQgnwZDSO23OKgQWZVglGliY3ezHZ6lVwC24Vjkmq/2yBSLakZE 6DZUjZzCW1nvtRK05ebyK6tofRsx8xB8pL/kcBb9nCuh70aLR+5cmE41X4O+MVJbwfP5s/RW 9BFSL3qgXuXso/3XuWTQjJJGgKhB6xXjMmb1J4q/h5IuVV4juv1Fem9sfmyrh+Wi5V1IzKI7 RPJ3KVb937eBgSENk53P0gUorwzUcO+ASEo3Z1cBKkJSPigDbeEjVfXQMzNt0oDRzpQqH2vp apo2jHnidWt8BsckuWZpxcZ9+/9obQ55DyVQHGiTN39hkETy3Emdnz1JVHTU0Q== Message-ID: <4189f993-b79b-b07f-4019-b1a1c9e192a0@redhat.com> Date: Wed, 17 Jun 2020 16:42:52 +0200 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: <87tuz9wzwq.fsf@linaro.org> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/16 23:30:45 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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 , Prasad J Pandit , Li Qiang , Li Qiang , qemu-devel@nongnu.org, P J P , Lei Sun , Alex Williamson , =?UTF-8?Q?Herv=c3=a9_Poussineau?= , Joel Stanley , Li Qiang , Paolo Bonzini , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/17/20 4:05 PM, Alex Bennée wrote: > > Philippe Mathieu-Daudé writes: > >> On 6/17/20 3:06 PM, Alex Williamson wrote: >>> On Wed, 17 Jun 2020 16:39:56 +1000 >>> David Gibson wrote: >>> >>>> On Wed, Jun 17, 2020 at 11:09:27AM +0530, P J P wrote: >>>>> From: Prasad J Pandit >>>>> >>>>> Hello, >>>>> >>>>> This series adds various undefined MMIO read/write functions >>>>> to avoid potential guest crash via a NULL pointer dereference. >>>> >>>> Hrm. If this is such a common problem, maybe we should just add a >>>> NULL check in the common paths. >>> >>> +1, clearly the behavior is already expected. Thanks, >> >> 20 months ago Peter suggested: >> >> "assert that every MemoryRegionOps has pointers to callbacks >> in it, when it is registered in memory_region_init_io() and >> memory_region_init_rom_device_nomigrate()." >> >> https://www.mail-archive.com/qemu-devel@nongnu.org/msg573310.html >> >> Li Qiang refers to this post from Paolo: >> >>> static const MemoryRegionOps notdirty_mem_ops = { >>> + .read = notdirty_mem_read, >>> .write = notdirty_mem_write, >>> .valid.accepts = notdirty_mem_accepts, >>> .endianness = DEVICE_NATIVE_ENDIAN, >> >> "This cannot happen, since TLB_NOTDIRTY is only added >> to the addr_write member (see accel/tcg/cputlb.c)." >> >> https://www.mail-archive.com/qemu-devel@nongnu.org/msg561345.html > > What about catching it in memory_region_dispatch_write: > > if (mr->ops->write) { > return access_with_adjusted_size(addr, &data, size, > mr->ops->impl.min_access_size, > mr->ops->impl.max_access_size, > memory_region_write_accessor, mr, > attrs); > } else if (mr->ops->write_with_attrs) { > return > access_with_adjusted_size(addr, &data, size, > mr->ops->impl.min_access_size, > mr->ops->impl.max_access_size, > memory_region_write_with_attrs_accessor, > mr, attrs); > } else { > qemu_log_mask(LOG_UNIMP|LOG_GUEST_ERROR, "%s: %s un-handled write\n", > __func__, mr->name); The problem is what return value to return... MEMTX_OK/MEMTX_ERROR/MEMTX_DECODE_ERROR? This is very device-specific and can't be decided here for all the cases. Better to abort() and fix each device? > } > >