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

Christoph Hellwig
2024-11-06T15:45:53Z

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.

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.