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[34.126.98.232]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-759cbd66eecsm10238885b3a.142.2025.07.23.11.58.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Jul 2025 11:58:25 -0700 (PDT) Date: Wed, 23 Jul 2025 18:58:20 +0000 From: Pranjal Shrivastava To: Nicolin Chen Cc: jgg@nvidia.com, will@kernel.org, joro@8bytes.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org Subject: Re: [PATCH v3 2/2] iommu/arm-smmu-v3: Replace vsmmu_size/type with get_viommu_size Message-ID: References: <20250721200444.1740461-1-nicolinc@nvidia.com> <20250721200444.1740461-3-nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jul 23, 2025 at 11:05:26AM -0700, Nicolin Chen wrote: > On Wed, Jul 23, 2025 at 01:37:53PM +0000, Pranjal Shrivastava wrote: > > On Mon, Jul 21, 2025 at 01:04:44PM -0700, Nicolin Chen wrote: > > > @@ -1273,6 +1279,10 @@ tegra241_cmdqv_init_vintf_user(struct arm_vsmmu *vsmmu, > > > phys_addr_t page0_base; > > > int ret; > > > > > > + /* Unsupported type was rejected in tegra241_cmdqv_get_vintf_size() */ > > > + if (WARN_ON(vsmmu->core.type != IOMMU_VIOMMU_TYPE_TEGRA241_CMDQV)) > > > + return -EOPNOTSUPP; > > > + > > > > Nit: I don't think we'd expect a call to this if the vintf_size returned > > 0? I see that in iommufd_viommu_alloc_ioctl, we already have a check: > > It's added in the previous patch where I explained that this is > to detect data corruption. When something like that happens, it > would be often illogical. > Right.. I got mis-led by the comment, my point is that if an "unsupported type" was rejected in _get_vintf_size, we wouldn't be here calling viommu_init since we error out based on the check in iommufd_viommu_alloc_ioctl.. but yes, if there was some data corruption that changed the viommu type between these calls, I guess it makes sense to check and error out here. > > And call ops->viommu_init only when the above isn't met. Thus, > > if we still end up calling ops->viommu_init, shouldn't we BUG_ON() it? > > I'd rather have the core code handle such things (since the driver is > > simply implementing the ops) and BUG_ON() something that's terribly > > wrong.. > > BUG_ON is discouraged following the coding style: > https://docs.kernel.org/process/coding-style.html#use-warn-rather-than-bug > Noted. Thanks. > > I can't see any ops->viommu_init being called elsewhere atm, let me > > know if there's a different path that I missed.. > > I see it as a precaution that should never get triggered. But in > case that it happens, I don't want it to proceed further wasting > precious HW resource given that this function allocates a VINTF. > Agreed. > Nicolin Praan