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

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Date:	Tue, 6 Oct 2015 18:28:15 +0300
From:	Vlad Zolotarov <vladz@...udius-systems.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...lladb.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 10/06/15 17:56, Michael S. Tsirkin wrote:
> On Tue, Oct 06, 2015 at 05:43:50PM +0300, Vlad Zolotarov wrote:
>> The only "like VFIO" behavior we implement here is binding the MSI-X
>> interrupt notification to eventfd descriptor.
> There will be more if you add some basic memory protections.

I've already explained that there is no need for any additional memory 
protections since it won't be able to protect anything.

>
> Besides, that's not true.
> Your patch queries MSI capability, sets # of vectors.

My patch doesn't set # of vectors.

> You even hinted you want to add BAR mapping down the road.
>
> VFIO does all of that.
>
>> This doesn't justifies the
>> hassle of implementing IOMMU-less VFIO mode.
> This applies to both VFIO and UIO really.  I'm not sure the hassle of
> maintaining this functionality in tree is justified.  It remains to be
> seen whether there are any users that won't taint the kernel.
> Apparently not in the current form of the patch, but who knows.

Again, uio_pci_generic with my patch simply follows the UIO design and 
in addition allows mapping MSI-X interrupts to eventfd's and it does it 
much more laconically compared to VFIO. Therefore these two modules 
won't be more related than they are today.

thanks,
vlad

>

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