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Tue, 13 Apr 2021 08:29:16 -0700 (PDT) Received: from [192.168.1.11] ([71.212.131.83]) by smtp.gmail.com with ESMTPSA id c11sm14463708pgk.83.2021.04.13.08.29.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 13 Apr 2021 08:29:15 -0700 (PDT) Subject: Re: [PATCH] accel/tcg: Fix translation exception on invalid instruction To: Ilya Leoshkevich , Paolo Bonzini References: <20210413132349.20520-1-iii@linux.ibm.com> From: Richard Henderson Message-ID: Date: Tue, 13 Apr 2021 08:29:13 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210413132349.20520-1-iii@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1031; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1031.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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: Christian Borntraeger , Cornelia Huck , qemu-devel@nongnu.org, David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/13/21 6:23 AM, Ilya Leoshkevich wrote: > * When tb_gen_code() is called on that page, tb->size ends up being 0 This is the bug, in target/s390x. Perhaps we need to add an assert that size != 0 after translation... > Fix by special-casing tb->size == 0: since there is no useful code, we > don't need to link pages in this case. Yes we do, because we need to link to the page to notice when changes to that page occur. While this won't happen in the specific case of uretprobe, it affects every other instance of a TB which begins with an illegal instruction. r~