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[34.140.83.185]) by smtp.gmail.com with ESMTPSA id ps10-20020a170906bf4a00b00a368718314dsm1289315ejb.7.2024.02.01.03.32.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Feb 2024 03:32:46 -0800 (PST) Date: Thu, 1 Feb 2024 11:32:41 +0000 From: Mostafa Saleh To: Jason Gunthorpe Cc: iommu@lists.linux.dev, Joerg Roedel , linux-arm-kernel@lists.infradead.org, Robin Murphy , Will Deacon , Moritz Fischer , Moritz Fischer , Michael Shavit , Nicolin Chen , patches@lists.linux.dev, Shameer Kolothum Subject: Re: [PATCH v4 02/16] iommu/arm-smmu-v3: Consolidate the STE generation for abort/bypass Message-ID: References: <0-v4-c93b774edcc4+42d2b-smmuv3_newapi_p1_jgg@nvidia.com> <2-v4-c93b774edcc4+42d2b-smmuv3_newapi_p1_jgg@nvidia.com> <20240131144702.GJ1455070@nvidia.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240131144702.GJ1455070@nvidia.com> On Wed, Jan 31, 2024 at 10:47:02AM -0400, Jason Gunthorpe wrote: > On Wed, Jan 31, 2024 at 02:40:24PM +0000, Mostafa Saleh wrote: > > > +static void arm_smmu_make_bypass_ste(struct arm_smmu_ste *target) > > > +{ > > > + memset(target, 0, sizeof(*target)); > > > > I see this can be used with the actual STE. Although this is done at init, but > > briefly making the STE abort from “arm_smmu_make_bypass_ste”, seems a bit > > fragile to me, in case we use this in the future in different scenarios, it > > might break the hitless assumption. But no strong opinion though. > > At init time, when that case happens, the STE table hasn't been > installed in the HW yet. This is why that specific code path has been > directly manipulating the STE and does not call the normal update path > with the sync'ing. > > It is perhaps subtle that is why it is a different flow. > > (this is also why I moved the function order as it was a bit obscure > to see that indeed all this stuff was sequenced right and we were not > updating a live STE improperly) I agree, this is not an issue, but it was just confusing when I first read it as “arm_smmu_make_bypass_ste” would make the STE transiently unavailable, and I had to go and check the usage. Maybe we can add a comment to clarify how this function is expected to be used. 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