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Mon, 18 Jan 2021 18:09:34 -0800 (PST) Received: from localhost ([211.108.35.36]) by smtp.gmail.com with ESMTPSA id s65sm5674942pfc.95.2021.01.18.18.09.33 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Mon, 18 Jan 2021 18:09:33 -0800 (PST) Date: Tue, 19 Jan 2021 11:09:31 +0900 From: Minwoo Im To: Klaus Jensen Subject: Re: [PATCH v2 02/12] hw/block/nvme: fix 64 bit register hi/lo split writes Message-ID: <20210119020931.GA5939@localhost.localdomain> References: <20210118094705.56772-1-its@irrelevant.dk> <20210118094705.56772-3-its@irrelevant.dk> <20210118124100.GB18718@localhost.localdomain> <20210118125945.GI18718@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) Received-SPF: pass client-ip=2607:f8b0:4864:20::1033; envelope-from=minwoo.im.dev@gmail.com; helo=mail-pj1-x1033.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, FREEMAIL_FROM=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: Fam Zheng , Kevin Wolf , qemu-block@nongnu.org, Klaus Jensen , qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , Keith Busch Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 21-01-18 20:53:24, Klaus Jensen wrote: > On Jan 18 21:59, Minwoo Im wrote: > > > The spec requires aligned 32 bit accesses (or the size of the register), > > > so maybe it's about time we actually ignore instead of falling through. > > > > Agreed. > > > > On the other hand. > > The spec just allows undefined behavior if the alignment or size > requirement is violated. So falling through is not wrong. If so, maybe we just can make this MMIO region support under 4bytes access with error messaging. I don't think we should not support them on purpose because spec says it just results in undefined behaviors which is just undefined how to handle them.