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Re: [PATCH V6 00/24] IOREQ feature (+ virtio-mmio) on Arm

On 29.01.21 10:13, Wei Chen wrote:
Hi Oleksandr,

Hi Wei

I just tested the v6 and the latest backend service with the latest staging 
They work well.

Tested-by: Wei Chen <Wei.Chen@xxxxxxx>

Thank you, I appreciate your help!

Wei Chen

-----Original Message-----
From: Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>
Sent: 2021年1月29日 9:48
To: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>; Paul Durrant
<paul@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>;
Wei Liu <wl@xxxxxxx>; Julien Grall <Julien.Grall@xxxxxxx>; George Dunlap
<george.dunlap@xxxxxxxxxx>; Ian Jackson <iwj@xxxxxxxxxxxxxx>; Julien Grall
<julien@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Jun Nakajima
<jun.nakajima@xxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>; Tim Deegan
<tim@xxxxxxx>; Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>; Volodymyr
Babchuk <Volodymyr_Babchuk@xxxxxxxx>; Bertrand Marquis
<Bertrand.Marquis@xxxxxxx>; Wei Chen <Wei.Chen@xxxxxxx>; Kaly Xin
<Kaly.Xin@xxxxxxx>; Artem Mygaiev <joculator@xxxxxxxxx>; Alex Bennée
Subject: [PATCH V6 00/24] IOREQ feature (+ virtio-mmio) on Arm

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Hello all.

The purpose of this patch series is to add IOREQ/DM support to Xen on Arm.
You can find an initial discussion at [1] and RFC-V5 series at [2]-[7].
Xen on Arm requires some implementation to forward guest MMIO access to a
model in order to implement virtio-mmio backend or even mediator outside of
As Xen on x86 already contains required support this series tries to make it
and introduce Arm specific bits plus some new functionality. Patch series is
based on
Julien's PoC "xen/arm: Add support for Guest IO forwarding to a device
Besides splitting existing IOREQ/DM support and introducing Arm side, the series
also includes virtio-mmio related changes (last 2 patches for toolstack)
for the reviewers to be able to see how the whole picture could look like
and give it a try.

According to the initial/subsequent discussions there are a few open
questions/concerns regarding security, performance in VirtIO solution:
1. virtio-mmio vs virtio-pci, SPI vs MSI, or even a composition of virtio-mmio +
    different use-cases require different transport...
2. virtio backend is able to access all guest memory, some kind of protection
    is needed: 'virtio-iommu in Xen' vs 'pre-shared-memory & memcpys in guest',
    (for these Alex have provided some input at [8])
3. interface between toolstack and 'out-of-qemu' virtio backend, avoid using
    Xenstore in virtio backend if possible. Also, there is a desire to make 
    backend hypervisor-agnostic.
4. a lot of 'foreing mapping' could lead to the memory exhaustion at the host
    as we are stealing the page from host memory in order to map the guest page.
    Julien has some idea regarding that.
5. Julien also has some ideas how to optimize the IOREQ code:
    5.1 vcpu_ioreq_handle_completion (former handle_hvm_io_completion)
which is called in
        an hotpath on Arm (everytime we are re-entering to the guest):
        Ideally, vcpu_ioreq_handle_completion should be a NOP (at max a few
        if there is nothing to do (if we don't have I/O forwarded to an IOREQ 
        Maybe we want to introduce a per-vCPU flag indicating if an I/O has been
        forwarded to an IOREQ server. This would allow us to bypass most of the
        if there is nothing to do.
    5.2 The current way to handle MMIO is the following:
        - Pause the vCPU
        - Forward the access to the backend domain
        - Schedule the backend domain
        - Wait for the access to be handled
        - Unpause the vCPU
        The sequence is going to be fairly expensive on Xen.
        It might be possible to optimize the ACK and avoid to wait for the 
        to handle the access.

Looks like all of them are valid and worth considering, but the first thing
which we need on Arm is a mechanism to forward guest IO to a device emulator,
so let's focus on it in the first place.



1. Current patch series doesn't contain VirtIO related changes for the toolstack
(but they are still available at the GitHub repo [9]):
- libxl: Introduce basic virtio-mmio support on Arm
- [RFC] libxl: Add support for virtio-disk configuration
I decided to skip these patches for now since they require some rework (not Xen
4.15 materials),
I will resume pushing them once we get *common* IOREQ in.

2. There are two new patches (according to the recent discussion) which likely
want Release-Ack:
- xen/ioreq: Do not let bufioreq to be used on other than x86 arches
- xen/ioreq: Make the IOREQ feature selectable on Arm
Also it feels to me that
- xen/dm: Introduce xendevicemodel_set_irq_level DM op
doesn't have all required Acks (at least for toolstack part).

3. I didn't manage to test patch-by-patch (in all possible modes for x86 and 
for this version how I did for all previous versions (due to the limited time),
but I performed selective build-testing for patches touched and with the whole


There are a lot of changes since RFC series, almost all TODOs were resolved on
Arm code was improved and hardened, common IOREQ/DM code became really
(without HVM-ism), the "legacy" mechanism of mapping magic pages for the
IOREQ servers
was left x86 specific, etc. But one TODO still remains which is "PIO handling" 
The "PIO handling" TODO is expected to left unaddressed for the current series.
It is not an big issue for now while Xen doesn't have support for vPCI on Arm.
On Arm64 they are only used for PCI IO Bar and we would probably want to
them to emulator as PIO access to make a DM completely arch-agnostic. So
"PIO handling"
should be implemented when we add support for vPCI.

There are patches on review this series depends on (but it was agreed that this
could go in without them):

Please note, that IOREQ feature is disabled by default on Arm within current
but there is a possibility to enable it via menuconfig.


Patch series [9] was rebased on recent "staging branch"
(6ca5101 x86/boot: Drop 'noapic' suggestion from check_timer()) and tested on
Renesas Salvator-X board + H3 ES3.0 SoC (Arm64) with virtio-mmio disk backend
running in driver domain and unmodified Linux Guest running on existing
virtio-blk driver (frontend). No issues were observed. Guest domain
use-cases work properly. Patch series was only build-tested on x86.

Please note, build-test passed for the following modes:
1. x86: CONFIG_HVM=y / CONFIG_IOREQ_SERVER=y (default)
2. x86: #CONFIG_HVM is not set / #CONFIG_IOREQ_SERVER is not set
4. Arm64: CONFIG_HVM=y / #CONFIG_IOREQ_SERVER is not set  (default)
6. Arm32: CONFIG_HVM=y / #CONFIG_IOREQ_SERVER is not set  (default)


Any feedback/help would be highly appreciated.

[1] https://lists.xenproject.org/archives/html/xen-devel/2020-
[2] https://lists.xenproject.org/archives/html/xen-devel/2020-
[3] https://lists.xenproject.org/archives/html/xen-devel/2020-
[4] https://lists.xenproject.org/archives/html/xen-devel/2020-
[5] https://lists.xenproject.org/archives/html/xen-devel/2020-
[6] https://lists.xenproject.org/archives/html/xen-devel/2021-
[7] https://lists.xenproject.org/archives/html/xen-devel/2021-
[8] https://lists.xenproject.org/archives/html/xen-devel/2020-
[9] https://github.com/otyshchenko1/xen/commits/ioreq_4.14_ml7
[10] https://github.com/otyshchenko1/virtio-disk/commits/ioreq_ml2

Julien Grall (3):
   xen/ioreq: Make x86's IOREQ related dm-op handling common
   xen/mm: Make x86's XENMEM_resource_ioreq_server handling common
   arm/ioreq: Introduce arch specific bits for IOREQ/DM features

Oleksandr Tyshchenko (21):
   x86/ioreq: Prepare IOREQ feature for making it common
   x86/ioreq: Add IOREQ_STATUS_* #define-s and update code for moving
   x86/ioreq: Provide out-of-line wrapper for the handle_mmio()
   xen/ioreq: Make x86's IOREQ feature common
   xen/ioreq: Make x86's hvm_ioreq_needs_completion() common
   xen/ioreq: Make x86's hvm_mmio_first(last)_byte() common
   xen/ioreq: Make x86's hvm_ioreq_(page/vcpu/server) structs common
   xen/ioreq: Move x86's ioreq_server to struct domain
   xen/ioreq: Move x86's io_completion/io_req fields to struct vcpu
   xen/ioreq: Remove "hvm" prefixes from involved function names
   xen/ioreq: Use guest_cmpxchg64() instead of cmpxchg()
   xen/arm: Call vcpu_ioreq_handle_completion() in check_for_vcpu_work()
   xen/mm: Handle properly reference in set_foreign_p2m_entry() on Arm
   xen/ioreq: Introduce domain_has_ioreq_server()
   xen/dm: Introduce xendevicemodel_set_irq_level DM op
   xen/arm: io: Abstract sign-extension
   xen/arm: io: Harden sign extension check
   xen/ioreq: Make x86's send_invalidate_req() common
   xen/arm: Add mapcache invalidation handling
   xen/ioreq: Do not let bufioreq to be used on other than x86 arches
   xen/ioreq: Make the IOREQ feature selectable on Arm

  MAINTAINERS                                  |    9 +-
  tools/include/xendevicemodel.h               |    4 +
  tools/libs/devicemodel/core.c                |   18 +
  tools/libs/devicemodel/libxendevicemodel.map |    1 +
  xen/arch/arm/Makefile                        |    2 +
  xen/arch/arm/dm.c                            |  149 +++
  xen/arch/arm/domain.c                        |    9 +
  xen/arch/arm/io.c                            |   30 +-
  xen/arch/arm/ioreq.c                         |  196 ++++
  xen/arch/arm/p2m.c                           |   51 +-
  xen/arch/arm/traps.c                         |   55 +-
  xen/arch/x86/Kconfig                         |    2 +-
  xen/arch/x86/hvm/dm.c                        |  134 +--
  xen/arch/x86/hvm/emulate.c                   |  220 ++--
  xen/arch/x86/hvm/hvm.c                       |   14 +-
  xen/arch/x86/hvm/hypercall.c                 |    9 +-
  xen/arch/x86/hvm/intercept.c                 |    5 +-
  xen/arch/x86/hvm/io.c                        |   52 +-
  xen/arch/x86/hvm/ioreq.c                     | 1368 ++----------------------
  xen/arch/x86/hvm/stdvga.c                    |   12 +-
  xen/arch/x86/hvm/svm/nestedsvm.c             |    2 +-
  xen/arch/x86/hvm/vmx/realmode.c              |    8 +-
  xen/arch/x86/hvm/vmx/vvmx.c                  |    5 +-
  xen/arch/x86/mm.c                            |   46 +-
  xen/arch/x86/mm/p2m-ept.c                    |    1 +
  xen/arch/x86/mm/p2m-pt.c                     |    1 +
  xen/arch/x86/mm/p2m.c                        |   17 +-
  xen/arch/x86/mm/shadow/common.c              |    2 +-
  xen/common/Kconfig                           |   12 +-
  xen/common/Makefile                          |    2 +
  xen/common/dm.c                              |   55 +
  xen/common/ioreq.c                           | 1429 ++++++++++++++++++++++++++
  xen/common/memory.c                          |   72 +-
  xen/include/asm-arm/domain.h                 |    2 +
  xen/include/asm-arm/ioreq.h                  |   70 ++
  xen/include/asm-arm/mmio.h                   |    1 +
  xen/include/asm-arm/p2m.h                    |   19 +-
  xen/include/asm-arm/traps.h                  |   25 +
  xen/include/asm-x86/hvm/domain.h             |   45 -
  xen/include/asm-x86/hvm/emulate.h            |    2 +-
  xen/include/asm-x86/hvm/io.h                 |   17 -
  xen/include/asm-x86/hvm/ioreq.h              |   39 +-
  xen/include/asm-x86/hvm/vcpu.h               |   18 -
  xen/include/asm-x86/ioreq.h                  |   39 +
  xen/include/asm-x86/mm.h                     |    4 -
  xen/include/asm-x86/p2m.h                    |   22 +-
  xen/include/public/hvm/dm_op.h               |   16 +
  xen/include/xen/dm.h                         |   44 +
  xen/include/xen/ioreq.h                      |  140 +++
  xen/include/xen/mm.h                         |    9 -
  xen/include/xen/p2m-common.h                 |    4 +
  xen/include/xen/sched.h                      |   34 +
  xen/include/xsm/dummy.h                      |    4 +-
  xen/include/xsm/xsm.h                        |    6 +-
  xen/xsm/dummy.c                              |    2 +-
  xen/xsm/flask/hooks.c                        |    5 +-
  56 files changed, 2722 insertions(+), 1837 deletions(-)
  create mode 100644 xen/arch/arm/dm.c
  create mode 100644 xen/arch/arm/ioreq.c
  create mode 100644 xen/common/dm.c
  create mode 100644 xen/common/ioreq.c
  create mode 100644 xen/include/asm-arm/ioreq.h
  create mode 100644 xen/include/asm-x86/ioreq.h
  create mode 100644 xen/include/xen/dm.h
  create mode 100644 xen/include/xen/ioreq.h



Oleksandr Tyshchenko



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