From: Oleksandr <olekstysh@gmail.com>
To: Julien Grall <julien@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>
Cc: "'Kevin Tian'" <kevin.tian@intel.com>,
"'Jun Nakajima'" <jun.nakajima@intel.com>,
"'Wei Liu'" <wl@xen.org>,
paul@xen.org, "'Andrew Cooper'" <andrew.cooper3@citrix.com>,
"'Ian Jackson'" <ian.jackson@eu.citrix.com>,
"'George Dunlap'" <george.dunlap@citrix.com>,
"'Tim Deegan'" <tim@xen.org>,
"'Oleksandr Tyshchenko'" <oleksandr_tyshchenko@epam.com>,
"'Julien Grall'" <julien.grall@arm.com>,
"Jan Beulich" <jbeulich@suse.com>,
xen-devel@lists.xenproject.org,
"'Roger Pau Monné'" <roger.pau@citrix.com>
Subject: Re: [RFC PATCH V1 01/12] hvm/ioreq: Make x86's IOREQ feature common
Date: Tue, 11 Aug 2020 13:10:19 +0300 [thread overview]
Message-ID: <dc6de2f4-8f9d-aa96-8513-aecedb11e0ef@gmail.com> (raw)
In-Reply-To: <441f4413-b746-035e-948e-da3ff76a9a3b@xen.org>
On 11.08.20 12:19, Julien Grall wrote:
Hi Julien, Stefano
> Hi Stefano,
>
> On 11/08/2020 00:34, Stefano Stabellini wrote:
>> On Mon, 10 Aug 2020, Oleksandr wrote:
>>> On 08.08.20 01:19, Oleksandr wrote:
>>>> On 08.08.20 00:50, Stefano Stabellini wrote:
>>>>> 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.
>>>>
>>>
>>> I optimized test patch a bit (now it looks much simpler). I didn't
>>> face any
>>> issues during a quick test.
>>
>> Both patches get much closer to following the proper state machine,
>> great! I think this patch is certainly a good improvement. I think the
>> other patch you sent earlier, slightly larger, is even better. It makes
>> the following additional changes that would be good to have:
>>
>> - try_fwd_ioserv returns IO_HANDLED on state == STATE_IORESP_READY
>> - handle_mmio simply calls do_trap_stage2_abort_guest
>
> I don't think we should call do_trap_stage2_abort_guest() as part of
> the completion because:
> * The function do_trap_stage2_abort_guest() is using registers
> that are not context switched (such as FAR_EL2). I/O handling is split
> in two with likely a context switch in the middle. The second part is
> the completion (i.e call to handle_mmio()). So the system registers
> will be incorrect.
> * A big chunk of do_trap_stage2_abort_guest() is not necessary for
> the completion. For instance, there is no need to try to translate the
> guest virtual address to a guest physical address.
>
> Therefore the version below is probably the best approach.
Indeed, the first version (with calling do_trap_stage2_abort_guest() for
a completion) is a racy. When testing it more heavily I faced an issue
(sometimes) which resulted in DomU got stuck completely.
(XEN) d2v1: vGICD: bad read width 0 r11 offset 0x000f00
I didn't investigate an issue in detail, but I assumed that code in
do_trap_stage2_abort_guest() caused that. This was the main reason why I
decided to optimize an initial patch (and took only advance_pc).
Reading Julien's answer I understand now what could happen.
--
Regards,
Oleksandr Tyshchenko
next prev parent reply other threads:[~2020-08-11 10:10 UTC|newest]
Thread overview: 140+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 18:21 [RFC PATCH V1 00/12] IOREQ feature (+ virtio-mmio) on Arm Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 01/12] hvm/ioreq: Make x86's IOREQ feature common Oleksandr Tyshchenko
2020-08-04 7:45 ` Paul Durrant
2020-08-04 11:10 ` Oleksandr
2020-08-04 11:23 ` Paul Durrant
2020-08-04 11:51 ` Oleksandr
2020-08-04 13:18 ` Paul Durrant
2020-08-04 13:52 ` Julien Grall
2020-08-04 15:41 ` Jan Beulich
2020-08-04 19:11 ` Stefano Stabellini
2020-08-05 7:01 ` Jan Beulich
2020-08-06 0:37 ` Stefano Stabellini
2020-08-06 6:59 ` Jan Beulich
2020-08-06 20:32 ` Stefano Stabellini
2020-08-07 13:19 ` Oleksandr
2020-08-07 16:45 ` Oleksandr
2020-08-07 21:50 ` Stefano Stabellini
2020-08-07 22:19 ` Oleksandr
2020-08-10 13:41 ` Oleksandr
2020-08-10 23:34 ` Stefano Stabellini
2020-08-11 9:19 ` Julien Grall
2020-08-11 10:10 ` Oleksandr [this message]
2020-08-11 22:47 ` Stefano Stabellini
2020-08-12 14:35 ` Oleksandr
2020-08-12 23:08 ` Stefano Stabellini
2020-08-13 20:16 ` Julien Grall
2020-08-07 23:45 ` Oleksandr
2020-08-10 23:34 ` Stefano Stabellini
2020-08-05 8:33 ` Julien Grall
2020-08-06 0:37 ` Stefano Stabellini
2020-08-06 9:45 ` Julien Grall
2020-08-06 23:48 ` Stefano Stabellini
2020-08-10 19:20 ` Julien Grall
2020-08-10 23:34 ` Stefano Stabellini
2020-08-11 11:28 ` Julien Grall
2020-08-11 22:48 ` Stefano Stabellini
2020-08-12 8:19 ` Julien Grall
2020-08-20 19:14 ` Oleksandr
2020-08-21 0:53 ` Stefano Stabellini
2020-08-21 18:54 ` Julien Grall
2020-08-05 13:30 ` Julien Grall
2020-08-06 11:37 ` Oleksandr
2020-08-10 16:29 ` Julien Grall
2020-08-10 17:28 ` Oleksandr
2020-08-05 16:15 ` Andrew Cooper
2020-08-06 8:20 ` Oleksandr
2020-08-15 17:30 ` Julien Grall
2020-08-16 19:37 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 02/12] hvm/dm: Make x86's DM " Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 03/12] xen/mm: Make x86's XENMEM_resource_ioreq_server handling common Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features Oleksandr Tyshchenko
2020-08-04 7:49 ` Paul Durrant
2020-08-04 14:01 ` Julien Grall
2020-08-04 23:22 ` Stefano Stabellini
2020-08-15 17:56 ` Julien Grall
2020-08-17 14:36 ` Oleksandr
2020-08-04 23:22 ` Stefano Stabellini
2020-08-05 7:05 ` Jan Beulich
2020-08-05 16:41 ` Stefano Stabellini
2020-08-05 19:45 ` Oleksandr
2020-08-05 9:32 ` Julien Grall
2020-08-05 15:41 ` Oleksandr
2020-08-06 10:19 ` Julien Grall
2020-08-10 18:09 ` Oleksandr
2020-08-10 18:21 ` Oleksandr
2020-08-10 19:00 ` Julien Grall
2020-08-10 20:29 ` Oleksandr
2020-08-10 22:37 ` Julien Grall
2020-08-11 6:13 ` Oleksandr
2020-08-12 15:08 ` Oleksandr
2020-08-11 17:09 ` Oleksandr
2020-08-11 17:50 ` Julien Grall
2020-08-13 18:41 ` Oleksandr
2020-08-13 20:36 ` Julien Grall
2020-08-13 21:49 ` Oleksandr
2020-08-13 20:39 ` Oleksandr Tyshchenko
2020-08-13 22:14 ` Julien Grall
2020-08-14 12:08 ` Oleksandr
2020-08-05 14:12 ` Julien Grall
2020-08-05 14:45 ` Jan Beulich
2020-08-05 19:30 ` Oleksandr
2020-08-06 11:08 ` Julien Grall
2020-08-06 11:29 ` Jan Beulich
2020-08-20 18:30 ` Oleksandr
2020-08-21 6:16 ` Jan Beulich
2020-08-21 11:13 ` Oleksandr
2020-08-06 13:27 ` Oleksandr
2020-08-10 18:25 ` Julien Grall
2020-08-10 19:58 ` Oleksandr
2020-08-05 16:13 ` Jan Beulich
2020-08-05 19:47 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 05/12] hvm/dm: Introduce xendevicemodel_set_irq_level DM op Oleksandr Tyshchenko
2020-08-04 23:22 ` Stefano Stabellini
2020-08-05 9:39 ` Julien Grall
2020-08-06 0:37 ` Stefano Stabellini
2020-08-06 11:32 ` Julien Grall
2020-08-06 23:49 ` Stefano Stabellini
2020-08-07 8:43 ` Jan Beulich
2020-08-07 21:50 ` Stefano Stabellini
2020-08-08 9:27 ` Julien Grall
2020-08-08 9:28 ` Julien Grall
2020-08-10 23:34 ` Stefano Stabellini
2020-08-11 13:04 ` Julien Grall
2020-08-11 22:48 ` Stefano Stabellini
2020-08-18 9:31 ` Julien Grall
2020-08-21 0:53 ` Stefano Stabellini
2020-08-17 15:23 ` Jan Beulich
2020-08-17 22:56 ` Stefano Stabellini
2020-08-18 8:03 ` Jan Beulich
2020-08-05 16:15 ` Jan Beulich
2020-08-05 22:12 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 06/12] libxl: Introduce basic virtio-mmio support on Arm Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 07/12] A collection of tweaks to be able to run emulator in driver domain Oleksandr Tyshchenko
2020-08-05 16:19 ` Jan Beulich
2020-08-05 16:40 ` Paul Durrant
2020-08-06 9:22 ` Oleksandr
2020-08-06 9:27 ` Jan Beulich
2020-08-14 16:30 ` Oleksandr
2020-08-16 15:36 ` Julien Grall
2020-08-17 15:07 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 08/12] xen/arm: Invalidate qemu mapcache on XENMEM_decrease_reservation Oleksandr Tyshchenko
2020-08-05 16:21 ` Jan Beulich
2020-08-06 11:35 ` Julien Grall
2020-08-06 11:50 ` Jan Beulich
2020-08-06 14:28 ` Oleksandr
2020-08-06 16:33 ` Jan Beulich
2020-08-06 16:57 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 09/12] libxl: Handle virtio-mmio irq in more correct way Oleksandr Tyshchenko
2020-08-04 23:22 ` Stefano Stabellini
2020-08-05 20:51 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 10/12] libxl: Add support for virtio-disk configuration Oleksandr Tyshchenko
2020-08-04 23:23 ` Stefano Stabellini
2020-08-05 21:12 ` Oleksandr
2020-08-06 0:37 ` Stefano Stabellini
2020-08-03 18:21 ` [RFC PATCH V1 11/12] libxl: Insert "dma-coherent" property into virtio-mmio device node Oleksandr Tyshchenko
2020-08-04 23:23 ` Stefano Stabellini
2020-08-05 20:35 ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 12/12] libxl: Fix duplicate memory node in DT Oleksandr Tyshchenko
2020-08-15 17:24 ` [RFC PATCH V1 00/12] IOREQ feature (+ virtio-mmio) on Arm Julien Grall
2020-08-16 19:34 ` Oleksandr
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