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[34.78.232.44]) by smtp.gmail.com with ESMTPSA id p13-20020a05600c358d00b003dd19baf45asm6427978wmq.40.2023.02.10.10.08.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Feb 2023 10:08:44 -0800 (PST) Date: Fri, 10 Feb 2023 18:08:39 +0000 From: Mostafa Saleh To: Peter Maydell Cc: qemu-devel@nongnu.org, jean-philippe@linaro.org, eric.auger@redhat.com, qemu-arm@nongnu.org Subject: Re: [PATCH v3] hw/arm/smmuv3: Add GBPA register Message-ID: References: <20230207181933.1999817-1-smostafa@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=2a00:1450:4864:20::333; envelope-from=smostafa@google.com; helo=mail-wm1-x333.google.com X-Spam_score_int: -175 X-Spam_score: -17.6 X-Spam_bar: ----------------- X-Spam_report: (-17.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_MED=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, ENV_AND_HDR_SPF_MATCH=-0.5, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5, USER_IN_DEF_SPF_WL=-7.5 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Feb 10, 2023 at 04:11:37PM +0000, Peter Maydell wrote: > > I think we should check the whole register against its reset value, > not just the ABORT bit. Otherwise if the guest writes the other fields > to non default values we won't migrate them. That doesn't change the > device behaviour now but it will have the weird effect that the guest > could write the register and then after a migration find it reading > back as a different value. Plus if in future we implement actual > functionality for any of the other fields then we'll want to know > what their true values written by the guest are. > > Linux never changes any fields except ABORT so for the most interesting > guest it won't make a difference right now. I agree, I was trying to achieve maximum backward compatibility as we don’t care about other fields, but this can be weird for forward migration, if the register is not fully migrated. And if SW touches this register it would probably want to configure the ABORT at some point, so it won’t help much for backward migration. I will update this in v4. Thanks, Mostafa