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Re: [PATCH V4 00/24] IOREQ feature (+ virtio-mmio) on Arm

On 14.01.21 05:55, Wei Chen wrote:
Hi Oleksandr,

Hi Wei.

I have tested this series with latest master and staging branches.
The virtio function works well for Arm as v3.

Thank you! This is good news.

For latest staging branch, it needs a tiny rebase for:
0011 xen/mm: Make x86's XENMEM_resource_ioreq_server handling common
As staging branch changes rapidly, I had done it manually and done the test.
It should not affect review.

Yes, very rapidly I would say) Yes, I will need to rebase due to the recent "xen/memory: Introduce CONFIG_ARCH_ACQUIRE_RESOURCE" patch

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


-----Original Message-----
From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of
Oleksandr Tyshchenko
Sent: 2021年1月13日 5:52
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>; Anthony PERARD
<anthony.perard@xxxxxxxxxx>; Bertrand Marquis <Bertrand.Marquis@xxxxxxx>;
Wei Chen <Wei.Chen@xxxxxxx>; Kaly Xin <Kaly.Xin@xxxxxxx>; Artem
Mygaiev <joculator@xxxxxxxxx>; Alex Bennée <alex.bennee@xxxxxxxxxx>
Subject: [PATCH V4 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-V3 series at [2]-[5].
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 the first two Alex have provided valuable input at [6])
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.


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. Also patch that makes DM code public was reworked
to have
the top level dm-op handling arch-specific and call into ioreq_server_dm_op()
for otherwise unhandled ops.
But one TODO still remains which is "PIO handling" on Arm.
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.

I left interface untouched in the following patch
"xen/dm: Introduce xendevicemodel_set_irq_level DM op"
since there is still an open discussion what interface to use/what
information to pass to the hypervisor.

There are patches on review this series depends on:

Please note, that IOREQ feature is disabled by default on Arm within current


Patch series [7] was rebased on recent "staging branch"
(7ba2ab4 x86/p2m: Fix paging_gva_to_gfn() for nested virt) 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/2020-
[7] https://github.com/otyshchenko1/xen/commits/ioreq_4.14_ml5
[8] https://github.com/xen-troops/virtio-disk/commits/ioreq_ml1

Julien Grall (5):
   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
   xen/dm: Introduce xendevicemodel_set_irq_level DM op
   libxl: Introduce basic virtio-mmio support on Arm

Oleksandr Tyshchenko (19):
   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: Stick around in leave_hypervisor_to_guest until I/O has
   xen/mm: Handle properly reference in set_foreign_p2m_entry() on Arm
   xen/ioreq: Introduce domain_has_ioreq_server()
   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
   [RFC] libxl: Add support for virtio-disk configuration

  MAINTAINERS                                  |    8 +-
  tools/include/xendevicemodel.h               |    4 +
  tools/libs/devicemodel/core.c                |   18 +
  tools/libs/devicemodel/libxendevicemodel.map |    1 +
  tools/libs/light/Makefile                    |    1 +
  tools/libs/light/libxl_arm.c                 |   94 +-
  tools/libs/light/libxl_create.c              |    1 +
  tools/libs/light/libxl_internal.h            |    1 +
  tools/libs/light/libxl_types.idl             |   16 +
  tools/libs/light/libxl_types_internal.idl    |    1 +
  tools/libs/light/libxl_virtio_disk.c         |  109 ++
  tools/xl/Makefile                            |    2 +-
  tools/xl/xl.h                                |    3 +
  tools/xl/xl_cmdtable.c                       |   15 +
  tools/xl/xl_parse.c                          |  116 +++
  tools/xl/xl_virtio_disk.c                    |   46 +
  xen/arch/arm/Makefile                        |    2 +
  xen/arch/arm/dm.c                            |  174 ++++
  xen/arch/arm/domain.c                        |    9 +
  xen/arch/arm/io.c                            |   30 +-
  xen/arch/arm/ioreq.c                         |  198 ++++
  xen/arch/arm/p2m.c                           |   51 +-
  xen/arch/arm/traps.c                         |   72 +-
  xen/arch/x86/Kconfig                         |    1 +
  xen/arch/x86/hvm/dm.c                        |  107 +-
  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                     | 1375 ++-----------------------
  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.c                        |   17 +-
  xen/arch/x86/mm/shadow/common.c              |    2 +-
  xen/common/Kconfig                           |    3 +
  xen/common/Makefile                          |    1 +
  xen/common/ioreq.c                           | 1426 ++++++++++++++++++++++++++
  xen/common/memory.c                          |   72 +-
  xen/include/asm-arm/domain.h                 |    3 +
  xen/include/asm-arm/hvm/ioreq.h              |   72 ++
  xen/include/asm-arm/mm.h                     |    8 -
  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             |   43 -
  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/mm.h                     |    4 -
  xen/include/asm-x86/p2m.h                    |   27 +-
  xen/include/public/arch-arm.h                |    5 +
  xen/include/public/hvm/dm_op.h               |   16 +
  xen/include/xen/dm.h                         |   39 +
  xen/include/xen/ioreq.h                      |  140 +++
  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 +-
  65 files changed, 3073 insertions(+), 1809 deletions(-)
  create mode 100644 tools/libs/light/libxl_virtio_disk.c
  create mode 100644 tools/xl/xl_virtio_disk.c
  create mode 100644 xen/arch/arm/dm.c
  create mode 100644 xen/arch/arm/ioreq.c
  create mode 100644 xen/common/ioreq.c
  create mode 100644 xen/include/asm-arm/hvm/ioreq.h
  create mode 100644 xen/include/xen/dm.h
  create mode 100644 xen/include/xen/ioreq.h



Oleksandr Tyshchenko



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