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Tsirkin" To: Srujana Challa Cc: Christoph Hellwig , "virtualization@lists.linux.dev" , "kvm@vger.kernel.org" , "jasowang@redhat.com" , "eperezma@redhat.com" , Nithin Kumar Dabilpuram , Jerin Jacob , Greg Kroah-Hartman Subject: Re: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for NO-IOMMU mode Message-ID: <20241106131108-mutt-send-email-mst@kernel.org> References: <20241016134127-mutt-send-email-mst@kernel.org> <20241019201059-mutt-send-email-mst@kernel.org> <20241023041739-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: PMkf1-LU_zr2wdHIIw8Y3-XQvU3KYKFXiITFE0gFNFk_1730916713 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Wed, Nov 06, 2024 at 12:38:02PM +0000, Srujana Challa wrote: > > Subject: Re: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for NO- > > IOMMU mode > > > > On Wed, Oct 23, 2024 at 04: 19: 02AM -0400, Michael S. Tsirkin wrote: > On > > Tue, Oct 22, 2024 at 11: 58: 19PM -0700, Christoph Hellwig wrote: > > On Sat, > > Oct 19, 2024 at 08: 16: 44PM -0400, Michael S. Tsirkin wrote: > > > Because > > > > On Wed, Oct 23, 2024 at 04:19:02AM -0400, Michael S. Tsirkin wrote: > > > On Tue, Oct 22, 2024 at 11:58:19PM -0700, Christoph Hellwig wrote: > > > > On Sat, Oct 19, 2024 at 08:16:44PM -0400, Michael S. Tsirkin wrote: > > > > > Because people want to move from some vendor specific solution > > > > > with vfio to a standard vdpa compatible one with vdpa. > > > > > > > > So now you have a want for new use cases and you turn that into a > > > > must for supporting completely insecure and dangerous crap. > > > > > > Nope. > > > > > > kernel is tainted -> unsupported > > > > > > whoever supports tainted kernels is already in dangerous waters. > > > > That's not a carte blanche for doing whatever crazy stuff you want. > > > > And if you don't trust me I'll add Greg who has a very clear opinion on > > IOMMU-bypassing user I/O hooks in the style of the uio driver as well I think > > :) > > It is going in circles, let me give the summary, > Issue: We need to address the lack of no-IOMMU support in the vhost vDPA driver for better performance. > Measured Performance: On the machine "13th Gen Intel(R) Core(TM) i9-13900K, 32 Cores", we observed > a performance improvement of 70 - 80% with intel_iommu=off when we run high-throughput network > packet processing. > Rationale for Fix: High-end machines which gives better performance with IOMMU are very expensive, > and certain use cases, such as embedded environment and trusted applications, do not require > the security features provided by IOMMU. > Initial Approach: We initially considered a driver-based solution, specifically integrating no-IOMMU > support into Marvell’s octep-vdpa driver. > Initial Community Feedback: The community suggested adopting a VFIO-like scheme to make the solution > more generic and widely applicable. > Decision Point: Should we pursue a generic approach for no-IOMMU support in the vhost vDPA driver, > or should we implement a driver-specific solution? > > Thanks, > Srujana. This point does not matter for Christoph. -- MST