Re: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for NO-IOMMU mode

Michael S. Tsirkin
2024-11-06T18:11:56Z

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.

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MST