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

[Gleb Natapov <gleb@scylladb.com>]

On Thu, Oct 08, 2015 at 12:38:28PM +0300, Michael S. Tsirkin wrote:
> 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.
> 
It still can be used safely with same devices. Admittedly I did not look
close, but I am sure the patch does not enable bus mastering if MSI
interrupt is not requested. If not, well that can be fixed. But more
importantly it can be used unsafely in its current state. Not only can,
it is widely used so.

> [mst@robin linux]$ git grep pci_set_master|wc -l 533
> [mst@robin 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.
> 
Have you commented about this on the patch and it was not fixed?

--
			Gleb.