Caitlin> True, but how does that constrain the local interfaces by
Caitlin> which the driver is informed of the set of pages that
Caitlin> back a given memory region? The driver must still
Caitlin> ultimately provide dma accessible addresses to the
Caitlin> device. RDMA just changes the timing of the steps, albeit
Caitlin> radically, but not what the steps are.
It's only a problem for "reserved L_Key" types of things, where the
device is supposed to just use the address given in a work request
without translating it. No translation means that work requests have
to contain "bus addresses" -- addresses that are what the device would
put on the bus to access memory. But if a device needs to simulate
DMA in software, then it really needs a kernel virtual address, not a
bus address. But it's pretty ugly to have to put that knowledge in
every consumer.
- R.
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