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

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Date:	Thu, 8 Oct 2015 12:38:28 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...lladb.com>
Cc:	Avi Kivity <avi@...lladb.com>,
	Alex Williamson <alex.williamson@...hat.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 Thu, Oct 08, 2015 at 10:59:10AM +0300, Gleb Natapov wrote:
> I do not remember this been an issue when uio_generic was accepted
> into the kernel. The reason was because it meant to be accessible by root
> only.

No - because it does not need bus mastering. So it can be used safely
with some devices.

[mst@...in linux]$ git grep pci_set_master|wc -l 533
[mst@...in linux]$ git grep pci_enable|wc -l 1597

Looks like about 2/3 devices don't need to be bus masters.

It's up to admin not to bind it to devices, and that is unfortunate,
but manually binding an incorrect driver to a device is generally
a hard problem to solve.

> > There's also drivers/vfio/virqfd.c which deals
> > with sending interrupts over eventfds correctly.
> > 
> As opposite to this patch that deals with them incorrectly? In what way?

cleanup on fd close is not handled.

-- 
MST
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