From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@scylladb.com>
Subject: Re: Having troubles binding an SR-IOV VF to
 uio_pci_generic on Amazon instance
Date: Thu, 1 Oct 2015 14:34:00 +0300
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On 10/01/2015 02:31 PM, Michael S. Tsirkin wrote:
> On Thu, Oct 01, 2015 at 02:20:37PM +0300, Avi Kivity wrote:
>>
>> On 10/01/2015 02:09 PM, Michael S. Tsirkin wrote:
>>> On Thu, Oct 01, 2015 at 01:50:10PM +0300, Avi Kivity wrote:
>>>>>> It's not just the lack of system calls, of course, the architecture is
>>>>>> completely different.
>>>>> Absolutely - I'm not saying move all of DPDK into kernel.
>>>>> We just need to protect the RX rings so hardware does
>>>>> not corrupt kernel memory.
>>>>>
>>>>>
>>>>> Thinking about it some more, many devices
>>>>> have separate rings for DMA: TX (device reads memory)
>>>>> and RX (device writes memory).
>>>>> With such devices, a mode where userspace can write TX ring
>>>>> but not RX ring might make sense.
>>>> I'm sure you can cause havoc just by reading, if you read from I/O memory.
>>> Not talking about I/O memory here. These are device rings in RAM.
>> Right.  But you program them with DMA addresses, so the device can read
>> another device's memory.
> It can't if host has limited it to only DMA into guest RAM, which is
> pretty common.
>

Ok.  So yes, the tx ring can be mapped R/W.