Re: [PATCH v4 06/17] KVM: arm64: Add pkvm_hyp_req infrastructure

Vincent Donnefort [off-list ref] writes:

Introduce a struct pkvm_hyp_req to enable the pKVM hypervisor to request
resources from the host.

Provide serialisation helpers to transport these requests via SMCCC
registers (starting from a2):

  pkvm_hyp_req_to_smccc() to encode into the SMCCC args.
  smccc_to_pkvm_hyp_req() to decode them.

When the hypervisor raises a request, the host must handle it and retry
the HVC. To automate this sequence, introduce the pkvm_call_hyp_req()
macro. This intercepts pending requests, invokes the handler and retries
the HVC.

Additionally, introduce a trace event to track the handling of these
requests.

Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Signed-off-by: Vincent Donnefort <redacted>

This is very similar to the memory-transferring SRO operations described
in section B4.3, RMI operations, of https://support.arm.com/documentation/den0137/2-0bet3/

The SRO model covers more details than the pkvm_hyp_req infrastructure.
Should we look at making the two more similar?

-aneesh