linux-kernel - Re: vPASID capability for VF

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Message-ID: <ZFrMneCMKuCtu7JF@nvidia.com>
Date:   Tue, 9 May 2023 19:43:41 -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 Tue, May 09, 2023 at 08:34:53AM +0000, Tian, Kevin wrote:
> According to PCIe spec (7.8.9 PASID Extended Capability Structure):
> 
>   The PASID configuration of the single non-VF Function representing
>   the device is also used by all VFs in the device. A PF is permitted
>   to implement the PASID capability, but VFs must not implement it.
> 
> To enable PASID on VF then one open is where to locate the PASID
> capability in VF's vconfig space. vfio-pci doesn't know which offset
> may contain VF specific config registers. Finding such offset must
> come from a device specific knowledge.

Why? Can't vfio probe the cap tree and just find a gap to insert a new
cap? We already mangle the cap list, I'm not sure I see what
the problem is?

Jason