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Date: Tue, 16 Jan 2024 11:29:28 -0400
From: Jason Gunthorpe <jgg@ziepe.ca>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Baochen Qiang <quic_bqiang@quicinc.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Kalle Valo <kvalo@kernel.org>, James Prestwood <prestwoj@gmail.com>,
	linux-wireless@vger.kernel.org, ath11k@lists.infradead.org,
	iommu@lists.linux.dev
Subject: Re: ath11k and vfio-pci support
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On Tue, Jan 16, 2024 at 11:41:19AM +0100, David Woodhouse wrote:

> If we had had this posted interrupt support from the beginning, perhaps
> we could have have a much simpler model — we just let the guest write
> its intended (v)CPU#/vector *directly* to the MSI table in the device,
> and let the IOMMU fix it up by having a table pointing to the
> appropriate set of vCPUs. But that isn't how it happened. The model we
> have is that the VMM has to *emulate* the config space and handle the
> interrupts as described above.

I do have a strong desire to rework things to be more like this, just
not time yet :)

We have enough real problems related to the fake interrupt data in
the guest.

This ath11k thing sounds more like IMS really - it makes zero sense
that a device would be designed where the MSI vector has to be copied
to another location - most likely the other location is another
interrupt source that can be programmed independently, with its own
irqchip, etc? Linux supports this now. Thomas and Intel did it to
support SIOV IMS.

Are you sure you have implemented your Linux driver correctly? :)

Of course IMS doesn't work in VMs, but that is a big motivation to fix
the irq organizing. At least you'd know why the device is broken :)

Jason