Hi,
A few cents from the Realm support point of view.
On 05/02/2023 10:12, Marc Zyngier wrote:
On Fri, 03 Feb 2023 13:50:40 +0000,
James Morse <james.morse@xxxxxxx> wrote:
From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
When capability KVM_CAP_ARM_HVC_TO_USER is available, userspace can
request to handle all hypercalls that aren't handled by KVM. With the
help of another capability, this will allow userspace to handle PSCI
calls.
Suggested-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
---
On top of Oliver's ask not to make this a blanket "steal everything",
but instead to have an actual request for ranges of forwarded
hypercalls:
Notes on this implementation:
* A similar mechanism was proposed for SDEI some time ago [1]. This RFC
generalizes the idea to all hypercalls, since that was suggested on
the list [2, 3].
* We're reusing kvm_run.hypercall. I copied x0-x5 into
kvm_run.hypercall.args[] to help userspace but I'm tempted to remove
this, because:
- Most user handlers will need to write results back into the
registers (x0-x3 for SMCCC), so if we keep this shortcut we should
go all the way and read them back on return to kernel.
- QEMU doesn't care about this shortcut, it pulls all vcpu regs before
handling the call.
This may not be always possible, e.g., for Realms. GET_ONE_REG is
not supported. So using an explicit passing down of the args is
preferrable.
Thanks
Suzuki
