On Aug 1, 2023, at 6:46 PM, Jason Gunthorpe [off-list ref] wrote:

On Tue, Aug 01, 2023 at 07:06:57PM +0000, Long Li wrote:

quoted

The driver interrupt code limits the CPU processing time of each EQ
by reading a small batch of EQEs in this interrupt. It guarantees
all the EQs are checked on this CPU, and limits the interrupt
processing time for any given EQ. In this way, a bad EQ (which is
stormed by a bad user doing unreasonable re-arming on the CQ) can't
storm other EQs on this CPU.

Of course it can, the bad use just creates a million EQs and pushes a
bit of work through them constantly. How is that really any different
from pushing more EQEs into a single EQ?

And how does your EQ multiplexing work anyhow? Do you poll every EQ on
every interrupt? That itself is a DOS vector.

Jason

User does not create eqs directly . EQ creation is by product of opening device ie allocating context. I am not sure if the same process is allowed to open device multiple times - must be some kind of lock implemented. So million eqs are probably far fetched .
As for how the eq servicing is done - only those eq’s for which the interrupt is raised are checked. And each eq is tied only once and only to a single interrupt. 

Ajay