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Mon, 17 Aug 2026 05:22:16 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wvwM4-00000005tO2-0GS8; Mon, 17 Aug 2026 09:22:16 -0300 Date: Mon, 17 Aug 2026 09:22:16 -0300 From: Jason Gunthorpe To: Yu Zhang Cc: Jacob Pan , linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, iommu@lists.linux.dev, linux-pci@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, wei.liu@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, longli@microsoft.com, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, bhelgaas@google.com, kwilczynski@kernel.org, lpieralisi@kernel.org, mani@kernel.org, robh@kernel.org, arnd@arndb.de, mhklinux@outlook.com, tgopinath@linux.microsoft.com, easwar.hariharan@linux.microsoft.com, mrathor@linux.microsoft.com, baolu.lu@linux.intel.com, suravee.suthikulpanit@amd.com, vasant.hegde@amd.com Subject: Re: [PATCH v3 4/5] iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest Message-ID: <20260817122216.GD933791@ziepe.ca> References: <20260811155022.108148-1-zhangyu1@linux.microsoft.com> <20260811155022.108148-5-zhangyu1@linux.microsoft.com> <20260813152913.00003d8a@linux.microsoft.com> <20260813224627.GA933791@ziepe.ca> Precedence: bulk X-Mailing-List: linux-pci@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 Fri, Aug 14, 2026 at 05:37:48PM +0800, Yu Zhang wrote: > > Why check it at all? Is there an issue with attaching the same thing > > twice? Will it blip the DMA or something? > > Actually, I do not think there should be any issue with attaching twice. > Hyper-V *should* be able to accept such attachment. But I do not want to > make such assumption just for a redundant hypercall. > > Does this reasoning make sense, or would you prefer that I remove the > check? I would probably drop it. Having blocking always set blocking to the HW regardless of what the SW tracking state says feels more robust to me. Jason