Re: [RFC] /dev/ioasid uAPI proposal

From: Jason Gunthorpe
Date: Mon Jun 07 2021 - 14:01:11 EST

On Mon, Jun 07, 2021 at 08:51:42AM +0200, Paolo Bonzini wrote:
> On 07/06/21 05:25, Tian, Kevin wrote:
> > Per Intel SDM wbinvd is a privileged instruction. A process on the
> > host has no privilege to execute it.
> (Half of) the point of the kernel is to do privileged tasks on the
> processes' behalf. There are good reasons why a process that uses VFIO
> (without KVM) could want to use wbinvd, so VFIO lets them do it with a ioctl
> and adequate checks around the operation.

Yes, exactly.

You cannot write a correct VFIO application for hardware that uses the
no-snoop bit without access to wbinvd.

KVM or not does not matter.