On 08.08.20 00:50, Stefano Stabellini wrote:
Hi
On Fri, 7 Aug 2020, Oleksandr wrote:
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?
I think you should check the ioreq->state in try_fwd_ioserv(), if the
result is ready, then ioreq->state should be STATE_IORESP_READY, and you
can return IO_HANDLED.
That is assuming that you are looking at the live version of the ioreq
shared with QEMU instead of a private copy of it, which I am not sure.
Looking at try_fwd_ioserv() it would seem that vio->io_req is just a
copy? The live version is returned by get_ioreq() ?
If I understand the code correctly, indeed, get_ioreq() returns live
version shared with emulator.
Desired state change (STATE_IORESP_READY) what actually the
hvm_wait_for_io() is waiting for is set here (in my case):
https://xenbits.xen.org/gitweb/?p=people/pauldu/demu.git;a=blob;f=demu.c;h=f785b394d0cf141dffa05bdddecf338214358aea;hb=refs/heads/master#l698
Even in handle_hvm_io_completion, instead of setting vio->io_req.state
to STATE_IORESP_READY by hand, it would be better to look at the live
version of the ioreq because QEMU will have already set ioreq->state
to STATE_IORESP_READY (hw/i386/xen/xen-hvm.c:cpu_handle_ioreq).
It seems that after detecting STATE_IORESP_READY in hvm_wait_for_io()
the state of live version is set to STATE_IOREQ_NONE immediately, so
looking at the live version down the handle_hvm_io_completion()
or in try_fwd_ioserv() shows us nothing I am afraid.
--
Regards,
Oleksandr Tyshchenko
