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

Christoph Hellwig
2024-10-01T08:47:27Z

On Fri, Sep 20, 2024 at 07:35:28PM +0530, Srujana Challa wrote:
> This patchset introduces support for an UNSAFE, no-IOMMU mode in the
> vhost-vdpa driver. When enabled, this mode provides no device isolation,
> no DMA translation, no host kernel protection, and cannot be used for
> device assignment to virtual machines. It requires RAWIO permissions
> and will taint the kernel.
>
> This mode requires enabling the "enable_vhost_vdpa_unsafe_noiommu_mode"
> option on the vhost-vdpa driver and also negotiate the feature flag
> VHOST_BACKEND_F_NOIOMMU. This mode would be useful to get
> better performance on specifice low end machines and can be leveraged
> by embedded platforms where applications run in controlled environment.

... and is completely broken and dangerous.