linux-kernel - Re: [PATCH v3 0/3] uio: add MSI/MSI-X support to uio_pci

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Message-ID: <5614F3EA.5060208@scylladb.com>
Date:	Wed, 7 Oct 2015 13:28:58 +0300
From:	Avi Kivity <avi@...lladb.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...udius-systems.com>,
	Vlad Zolotarov <vladz@...udius-systems.com>,
	linux-kernel@...r.kernel.org, hjk@...sjkoch.de, corbet@....net,
	gregkh@...uxfoundation.org, bruce.richardson@...el.com,
	gleb@...udius-systems.com, stephen@...workplumber.org,
	alexander.duyck@...il.com
Subject: Re: [PATCH v3 0/3] uio: add MSI/MSI-X support to uio_pci_generic
 driver



On 10/07/2015 01:25 PM, Michael S. Tsirkin wrote:
> On Tue, Oct 06, 2015 at 07:09:11PM +0300, Avi Kivity wrote:
>>
>> On 10/06/2015 06:15 PM, Michael S. Tsirkin wrote:
>>>> While it is possible that userspace malfunctions and accidentally programs
>>>> MSI incorrectly, the risk is dwarfed by the ability of userspace to program
>>>> DMA incorrectly.
>>> That seems to imply that for the upstream kernel this is not a valid usecase at all.
>>>
>> That is trivially incorrect, upstream pci_uio_generic is used with dpdk for
>> years.
> dpdk used to do polling for years. patch to use interrupts was posted in
> june 2015.

dpdk used interrupts long before that.

>
>>   Are dpdk applications an invalid use case?
> The way dpdk is using UIO/sysfs is borderline at best, and can't be used
> to justify new interfaces.  They have a more secure mode using VFIO.
> That one's more reasonable.
>

Maybe this was not stressed enough times, but not all configurations 
have an iommu, or want to use one.

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