Re: [RFC] Legacy Virtio Driver with Device Has Limited Memory Access

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 18, 2024 at 07:15:47PM +0900, Shunsuke Mie wrote:
> Thank you for your response.
> 
> 2024年6月18日(火) 18:47 Michael S. Tsirkin <mst@redhat.com>:
> >
> > On Tue, Jun 18, 2024 at 08:41:09AM +0900, Shunsuke Mie wrote:
> > > Let's clarify the situation.
> > >
> > > The Virtio device and driver are not working properly due to a
> > > combination of the following reasons:
> > >
> > > 1. Regarding VIRTIO_F_ACCESS_PLATFORM:
> > > - The modern spec includes VIRTIO_F_ACCESS_PLATFORM, which allows
> > > Physical DMAC to be used.
> > > - This feature is not available in the legacy spec.
> >
> > ... because legacy drivers don't set it
> >
> > > 2. Regarding Virtio PCIe Capability:
> > > - The modern spec requires Virtio PCIe Capability.
> >
> > It's a PCI capability actually. People have been asking
> > about option to make it a pcie extended capability,
> > but no one did the spec, qemu and driver work, yet.
> >
> > > - In some environments, Virtio PCIe Capability cannot be provided.
> >
> > why not?
> PCIe Endpoint Controller chips are available from several vendors and allow
> software to describe the behavior of PCIe Endpoint functions. However, they
> offer only limited functionality. Specifically, while PCIe bus communication is
> programmable, PCIe Capabilities are fixed and cannot be made to show as
> virtio's.

Okay. So where could these structures live, if not in pci config?

-- 
MST