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

Srujana Challa
2024-11-07T06:08:51Z

> 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?
>
> 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.