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[34.78.232.44]) by smtp.gmail.com with ESMTPSA id i3-20020a5d5223000000b002bfae1398bbsm11805596wra.42.2023.02.07.10.08.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Feb 2023 10:08:00 -0800 (PST) Date: Tue, 7 Feb 2023 18:07:44 +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 v2] hw/arm/smmuv3: Add GBPA register Message-ID: References: <20230126141120.448641-1-smostafa@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=smostafa@google.com; helo=mail-wm1-x332.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=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@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-arm-bounces+alex.bennee=linaro.org@nongnu.org Sender: qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org X-TUID: jVEf0d+GUxtc Hi Peter, On Tue, Feb 07, 2023 at 02:03:02PM +0000, Peter Maydell wrote: > On Thu, 26 Jan 2023 at 14:12, Mostafa Saleh wrote: > > > > GBPA register can be used to globally abort all > > transactions. > > > > It is described in the SMMU manual in "6.3.14 SMMU_GBPA". > > ABORT reset value is IMPLEMENTATION DEFINED, it is chosen to > > be zero(Do not abort incoming transactions). > > > > Other fields have default values of Use Incoming. > > > > If UPDATE is not set, the write is ignored. This is the only permitted > > behavior in SMMUv3.2 and later.(6.3.14.1 Update procedure) > > > > As this patch adds a new state to the SMMU (GBPA), it is added > > in a new subsection for forward migration compatibility. > > > > Property "migrate-gbpa" was added to support backward compatibility. > > However, if the GBPA.ABORT is set from SW at time of migration, the > > GBPA migration will be forced to avoid inconsistencies where a qemu > > instance is aborting transactions and it is migrated to another > > instance bypassing them. > > Nothing ever sets the migrate-gpba property to anything > except its default 'true' value, so this (a) means that > it breaks migration compat and (b) seems a bit unneccessary. > > Can we say "migrate the field only if it is something other > than its reset value", not have the property, and get > migration compatibility that way ? > > Otherwise the patch looks OK. > > thanks > -- PMM Thanks for reviewing the patch. I am not really familiar with migration, My understanding that this would be set from cmdline(that is how I tested it). But yes, you are right, this is actually unnecessary, we can just migrate only if GBPA value is different from reset value. I will send v3 with this change. Thanks, Mostafa