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[159.2.73.22]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89c8534f9ccsm89564136d6.39.2026.03.23.06.54.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 06:54:15 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1w4fjS-000000004Z9-0f4n; Mon, 23 Mar 2026 10:54:14 -0300 Date: Mon, 23 Mar 2026 10:54:14 -0300 From: Jason Gunthorpe To: Tudor Ambarus Cc: Joerg Roedel , Will Deacon , Robin Murphy , Lorenzo Pieralisi , "Rob Herring (Arm)" , Joerg Roedel , Bjorn Helgaas , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, peter.griffin@linaro.org, andre.draszik@linaro.org, willmcvicker@google.com, jyescas@google.com, kernel-team@android.com, stable@vger.kernel.org Subject: Re: [PATCH] iommu: Fix bypass of IOMMU readiness check for multi-IOMMU devices Message-ID: <20260323135414.GA8437@ziepe.ca> References: <20260323-iommu-ready-check-v1-1-5f6fef8f9f59@linaro.org> 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: <20260323-iommu-ready-check-v1-1-5f6fef8f9f59@linaro.org> On Mon, Mar 23, 2026 at 01:09:27PM +0000, Tudor Ambarus wrote: > Commit da33e87bd2bf ("iommu: Handle yet another race around > registration") introduced a readiness check in `iommu_fwspec_init()` to > prevent client drivers from configuring their IOMMUs before > `bus_iommu_probe()` has completed. > > To optimize the replay path, the readiness check was conditionally > gated behind `!dev->iommu`: > if (!dev->iommu && !READ_ONCE(iommu->ready)) > return -EPROBE_DEFER; > > However, this assumption breaks down for devices that map to multiple > IOMMU instances. ?? We don't directly support "multiple IOMMU instances". There is only one dev->iommu. AFAIK if some drivers need to support multiple different instances of the same IOMMU driver they must deal with this fully internally and present to the core a "single instance" view. So, your explanation doesn't make sense to me. If dev->iommu is set then the driver must be ready, including any multi-instances it has. If it is not ready then this is really an iommu driver bug, not a core bug? Jason