Re: [dpdk-dev] Having troubles binding an SR-IOV VF to uio_pci_generic on Amazon instance

[Avi Kivity <avi@scylladb.com>]

On 10/01/2015 11:52 AM, Avi Kivity wrote:
>
>
> On 10/01/2015 11:44 AM, Michael S. Tsirkin wrote:
>> On Wed, Sep 30, 2015 at 11:40:16PM +0300, Michael S. Tsirkin wrote:
>>>> And for what, to prevent
>>>> root from touching memory via dma that they can access in a million other
>>>> ways?
>>> So one can be reasonably sure a kernel oops is not a result of a
>>> userspace bug.
>> Actually, I thought about this overnight, and  it should be possible to
>> drive it securely from userspace, without hypervisor changes.
>
> Also without the performance that was the whole reason from doing it 
> in userspace in the first place.
>
> I still don't understand your objection to the patch:
>
>> MSI messages are memory writes so any generic device capable
>> of MSI is capable of corrupting kernel memory.
>> This means that a bug in userspace will lead to kernel memory corruption
>> and crashes.  This is something distributions can't support.
>

And this:

> What userspace can't be allowed to do:
>
> 	access BAR
> 	write rings
>

It can access the BAR by mmap()ing the resourceN files under sysfs. 
You're not denying userspace the ability to oops the kernel, just the 
ability to do useful things with hardware.