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Date:   Wed, 30 Jun 2021 07:56:45 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     "Tian, Kevin" <kevin.tian@intel.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        David Woodhouse <dwmw2@infradead.org>,
        Jason Wang <jasowang@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Robin Murphy <robin.murphy@arm.com>,
        David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [RFC] /dev/ioasid uAPI proposal
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On Mon, Jun 07, 2021 at 03:25:32AM +0000, Tian, Kevin wrote:
> 
> Possibly just a naming thing, but I feel it's better to just talk about
> no-snoop or non-coherent in the uAPI. Per Intel SDM wbinvd is a
> privileged instruction. A process on the host has no privilege to 
> execute it. Only when this process holds a VM, this instruction matters
> as there are guest privilege levels. But having VFIO uAPI (which is
> userspace oriented) to explicitly deal with a CPU instruction which
> makes sense only in a virtualization context sounds a bit weird...

More importantly the Intel instructions here are super weird.
Pretty much every other architecture just has plan old cache
writeback/invalidate/writeback+invalidate instructions without all these
weird implications.