Re: [PATCH for-next 2/2] IB/hfi1: Make Unsupported Request error non-fatal

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On Thu, Apr 11, 2019 at 06:22:45PM +0000, Arumugam, Kamenee wrote:

> > What exactly is causing the UR?  Is it something the driver could
> > potentially avoid, e.g., an AtomicOp that HFI doesn't support?  I
> > have a > vague notion that InfiniBand allows some sort of direct
> > user-space access to hardware; is there something there that can
> > cause a UR?
> 
> HFI PCIe BAR are mapped to user space to implement kernel bypass for
> MPI/PSM jobs. In this case, user-level application is making
> spurious read accesses (invalid width access) to this memory mapping
> causing the device to report an unsupported request error through
> AER. The spurious read accesses may be due to errant application
> behavior (e.g. reading beyond the end of an array).

This is a device bug then. 

A RDMA device must accept and respond to all TLPs that the CPU could
create for the user accessible BAR pages.

A user process must not be able to crash the CPU or make the device
malfunction by accessing the exposed BAR page. This includes a broad
range of topics, like mis-aligned acceses, SSE instructions, atomics,
etc.

Is blocking AER even enough here? If the device isn't generating a
reasonable reply I have a bad feeling worse will happen.

Jason



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