linux-kernel - Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X

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Message-ID: <560DECE9.8020408@gmail.com>
Date:	Thu, 1 Oct 2015 19:33:13 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	hjk@...sjkoch.de, gregkh@...ux-foundation.org, dev@...k.org,
	linux-kernel@...r.kernel.org
Subject: Re: [dpdk-dev] [PATCH 2/2] uio: new driver to support PCI MSI-X

On 10/01/2015 05:04 PM, Stephen Hemminger wrote:
> On Thu, 1 Oct 2015 16:40:10 -0700
> Alexander Duyck <alexander.duyck@...il.com> wrote:
>
>> Do you really need to map IORESOURCE bars?  Most drivers I can think of
>> don't use IO BARs anymore.  Maybe we could look at just dropping the
>> code and adding it back later if we have a use case that absolutely
>> needs it.
> Mapping is not strictly necessary, but for virtio it acts a way to communicate
> the regions.

I think I see what you are saying.  I was hoping we could get away from 
having to map any I/O ports but it looks like virtio is still using them 
for BAR 0, or at least that is what I am seeing on my VM with 
virtio_net.  I was really hoping we could get away from that since a 16b 
address space is far too restrictive anyway.

>> Also how many devices actually need resources beyond BAR 0?  I'm just
>> curious as I know BAR 2 on many of the Intel devices is the register
>> space related to MSI-X so now we have both the PCIe subsystem and user
>> space with access to this region.
> VMXNet3 needs 2 bars. Most use only one.

So essentially we are needing to make exceptions for the virtual interfaces.

I guess there isn't much we can do then and we probably need to map any 
and all base address registers we can find for the given device.  I was 
hoping for something a bit more surgical since we are opening a security 
hole of sorts, but I guess it can't be helped if we want to support 
multiple devices and they all have such radically different configurations.

- Alex
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