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

Srujana Challa
2024-11-12T07:11:24Z

> Subject: RE: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for NO-
> IOMMU mode
>
> > Subject: Re: [EXTERNAL] Re: [PATCH v2 0/2] vhost-vdpa: Add support for
> > NO- IOMMU mode
> >
> > On Wed, Nov 06, 2024 at 12: 38: 02PM +0000, Srujana Challa wrote: > 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
> > On Wed, Nov 06, 2024 at 12:38:02PM +0000, Srujana Challa wrote:
> > > 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
> >
> > Looks ike you are going in circles indeed. Lack of performance is
> > never a reason to disable the basic memoy safety for userspace drivers.
> If security is a priority, the IOMMU should stay enabled. In that case, this
> patch wouldn’t cause any issues, right?
Another important aspect of this patch is that it enables vhost-vdpa functionality on machines that do not support IOMMU, such as the Intel® Core™ i5-2320 CPU @ 3.00GHz. I believe, this enhancement is essential as it broadens the compatibility of our system, allowing users with embedded or less advanced hardware to benefit from vhost-vdpa features.
Thanks.

> >
> > The (also quite bad) reason why vfio-nummu was added was to support
> > hardware entirely with an iommu.
> >
> > There is absolutely no reason to add krnel code for new methods of
> > unsafer userspace I/O without an IOMMU ever.