linux-kernel - Re: vPASID capability for VF

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Message-ID: <ZFwA9vAJAaoUi4xE@nvidia.com>
Date:   Wed, 10 May 2023 17:39:18 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Nicolin Chen <nicolinc@...dia.com>,
        "Lu, Baolu" <baolu.lu@...el.com>
Subject: Re: vPASID capability for VF

On Wed, May 10, 2023 at 02:16:05AM +0000, Tian, Kevin wrote:

> We don't have a control knob to hide/unhide a specific PCI cap
> today. It's hardcoded with proper virtualization policy in vfio-pci.
> 
> Following current convention once vfio-pci adds the support for the
> PASID cap it will be exposed if present (for VF it's the presence in PF).

We probably shouldn't do this - the PASID cap should only exist if the
VMM is actualy able to handle PASID throughout, and currently no VMM
does this.

So we can't just have the kernel unconditionally add the cap. There
needs to be a negotiation with the VMM

Jason