linux-kernel - Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

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Message-ID: <20151007225835-mutt-send-email-mst@redhat.com>
Date:	Wed, 7 Oct 2015 23:05:32 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Avi Kivity <avi@...lladb.com>,
	Vlad Zolotarov <vladz@...udius-systems.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, hjk@...sjkoch.de, corbet@....net,
	bruce.richardson@...el.com, avi@...udius-systems.com,
	gleb@...udius-systems.com, stephen@...workplumber.org,
	alexander.duyck@...il.com
Subject: Re: [PATCH v3 2/3] uio_pci_generic: add MSI/MSI-X support

On Wed, Oct 07, 2015 at 10:31:04AM -0600, Alex Williamson wrote:
> It sounds like a separate vfio iommu backend from type1, one that just
> pins the page and returns the bus address.  The curse and benefit would
> be that existing type1 users wouldn't "just work" in an insecure mode,
> the DMA mapping code would need to be aware of the difference.  Still, I
> do really prefer to keep vfio as only exposing a secure, iommu protected
> device to the user because surely someone will try and users would
> expect that removing iommu restrictions from vfio means they can do
> device assignment to VMs w/o an iommu.

What I had in mind is rather reusing vfio code.

What is needed is all the logic for handling device reset, protecting
BARs and config space regions, MSI/MSI-X and device-specific
work-arounds.

Also, all the interface things such as eventfd.

But I don't think it should be the same char device as vfio -
/dev/vfio/vfio is world-accessible - should be a separate non-world
accessible device, maybe /dev/vfio/noiommu.

This will ensure e.g. qemu does not attempts to use it automatically.
-- 
MST
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