On 06.08.20 03:37, Stefano Stabellini wrote:
Hi Stefano
Trying to simulate IO_RETRY handling mechanism (according to model
below) I continuously get IO_RETRY from try_fwd_ioserv() ...
OK, thanks for the details. My interpretation seems to be correct.
In which case, it looks like xen/arch/arm/io.c:try_fwd_ioserv should
return IO_RETRY. Then, xen/arch/arm/traps.c:do_trap_stage2_abort_guest
also needs to handle try_handle_mmio returning IO_RETRY the first
around, and IO_HANDLED when after QEMU does its job.
What should do_trap_stage2_abort_guest do on IO_RETRY? Simply return
early and let the scheduler do its job? Something like:
enum io_state state = try_handle_mmio(regs, hsr, gpa);
switch ( state )
{
case IO_ABORT:
goto inject_abt;
case IO_HANDLED:
advance_pc(regs, hsr);
return;
case IO_RETRY:
/* finish later */
return;
case IO_UNHANDLED:
/* IO unhandled, try another way to handle it. */
break;
default:
ASSERT_UNREACHABLE();
}
Then, xen/arch/arm/ioreq.c:handle_mmio() gets called by
handle_hvm_io_completion() after QEMU completes the emulation. Today,
handle_mmio just sets the user register with the read value.
But it would be better if it called again the original function
do_trap_stage2_abort_guest to actually retry the original operation.
This time do_trap_stage2_abort_guest calls try_handle_mmio() and gets
IO_HANDLED instead of IO_RETRY,
I may miss some important point, but I failed to see why try_handle_mmio
(try_fwd_ioserv) will return IO_HANDLED instead of IO_RETRY at this stage.
Or current try_fwd_ioserv() logic needs rework?
thus, it will advance_pc (the program
counter) completing the handling of this instruction.
The user register with the read value could be set by try_handle_mmio if
try_fwd_ioserv returns IO_HANDLED instead of IO_RETRY.
Is that how the state machine is expected to work?
--
Regards,
Oleksandr Tyshchenko
