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Laszlo Ersek dab30fbef3 acpi: cpuhp: fix guest-visible maximum access size to the legacy reg block
The modern ACPI CPU hotplug interface was introduced in the following
series (aa1dd39ca307..679dd1a957df), released in v2.7.0:

  1  abd49bc2ed docs: update ACPI CPU hotplug spec with new protocol
  2  16bcab97eb pc: piix4/ich9: add 'cpu-hotplug-legacy' property
  3  5e1b5d9388 acpi: cpuhp: add CPU devices AML with _STA method
  4  ac35f13ba8 pc: acpi: introduce AcpiDeviceIfClass.madt_cpu hook
  5  d2238cb678 acpi: cpuhp: implement hot-add parts of CPU hotplug
                  interface
  6  8872c25a26 acpi: cpuhp: implement hot-remove parts of CPU hotplug
                  interface
  7  76623d00ae acpi: cpuhp: add cpu._OST handling
  8  679dd1a957 pc: use new CPU hotplug interface since 2.7 machine type

Before patch#1, "docs/specs/acpi_cpu_hotplug.txt" only specified 1-byte
accesses for the hotplug register block.  Patch#1 preserved the same
restriction for the legacy register block, but:

- it specified DWORD accesses for some of the modern registers,

- in particular, the switch from the legacy block to the modern block
  would require a DWORD write to the *legacy* block.

The latter functionality was then implemented in cpu_status_write()
[hw/acpi/cpu_hotplug.c], in patch#8.

Unfortunately, all DWORD accesses depended on a dormant bug: the one
introduced in earlier commit a014ed07bd ("memory: accept mismatching
sizes in memory_region_access_valid", 2013-05-29); first released in
v1.6.0.  Due to commit a014ed07bd, the DWORD accesses to the *legacy*
CPU hotplug register block would work in spite of the above series *not*
relaxing "valid.max_access_size = 1" in "hw/acpi/cpu_hotplug.c":

> static const MemoryRegionOps AcpiCpuHotplug_ops = {
>     .read = cpu_status_read,
>     .write = cpu_status_write,
>     .endianness = DEVICE_LITTLE_ENDIAN,
>     .valid = {
>         .min_access_size = 1,
>         .max_access_size = 1,
>     },
> };

Later, in commits e6d0c3ce68 ("acpi: cpuhp: introduce 'Command data 2'
field", 2020-01-22) and ae340aa3d2 ("acpi: cpuhp: spec: add typical
usecases", 2020-01-22), first released in v5.0.0, the modern CPU hotplug
interface (including the documentation) was extended with another DWORD
*read* access, namely to the "Command data 2" register, which would be
important for the guest to confirm whether it managed to switch the
register block from legacy to modern.

This functionality too silently depended on the bug from commit
a014ed07bd.

In commit 5d971f9e67 ('memory: Revert "memory: accept mismatching sizes
in memory_region_access_valid"', 2020-06-26), first released in v5.1.0,
the bug from commit a014ed07bd was fixed (the commit was reverted).
That swiftly exposed the bug in "AcpiCpuHotplug_ops", still present from
the v2.7.0 series quoted at the top -- namely the fact that
"valid.max_access_size = 1" didn't match what the guest was supposed to
do, according to the spec ("docs/specs/acpi_cpu_hotplug.txt").

The symptom is that the "modern interface negotiation protocol"
described in commit ae340aa3d2:

> +      Use following steps to detect and enable modern CPU hotplug interface:
> +        1. Store 0x0 to the 'CPU selector' register,
> +           attempting to switch to modern mode
> +        2. Store 0x0 to the 'CPU selector' register,
> +           to ensure valid selector value
> +        3. Store 0x0 to the 'Command field' register,
> +        4. Read the 'Command data 2' register.
> +           If read value is 0x0, the modern interface is enabled.
> +           Otherwise legacy or no CPU hotplug interface available

falls apart for the guest: steps 1 and 2 are lost, because they are DWORD
writes; so no switching happens.  Step 3 (a single-byte write) is not
lost, but it has no effect; see the condition in cpu_status_write() in
patch#8.  And step 4 *misleads* the guest into thinking that the switch
worked: the DWORD read is lost again -- it returns zero to the guest
without ever reaching the device model, so the guest never learns the
switch didn't work.

This means that guest behavior centered on the "Command data 2" register
worked *only* in the v5.0.0 release; it got effectively regressed in
v5.1.0.

To make things *even more* complicated, the breakage was (and remains, as
of today) visible with TCG acceleration only.  Commit 5d971f9e67 makes
no difference with KVM acceleration -- the DWORD accesses still work,
despite "valid.max_access_size = 1".

As commit 5d971f9e67 suggests, fix the problem by raising
"valid.max_access_size" to 4 -- the spec now clearly instructs the guest
to perform DWORD accesses to the legacy register block too, for enabling
(and verifying!) the modern block.  In order to keep compatibility for the
device model implementation though, set "impl.max_access_size = 1", so
that wide accesses be split before they reach the legacy read/write
handlers, like they always have been on KVM, and like they were on TCG
before 5d971f9e67 (v5.1.0).

Tested with:

- OVMF IA32 + qemu-system-i386, CPU hotplug/hot-unplug with SMM,
  intermixed with ACPI S3 suspend/resume, using KVM accel
  (regression-test);

- OVMF IA32X64 + qemu-system-x86_64, CPU hotplug/hot-unplug with SMM,
  intermixed with ACPI S3 suspend/resume, using KVM accel
  (regression-test);

- OVMF IA32 + qemu-system-i386, SMM enabled, using TCG accel; verified the
  register block switch and the present/possible CPU counting through the
  modern hotplug interface, during OVMF boot (bugfix test);

- I do not have any testcase (guest payload) for regression-testing CPU
  hotplug through the *legacy* CPU hotplug register block.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Ani Sinha <ani@anisinha.ca>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Cc: qemu-stable@nongnu.org
Ref: "IO port write width clamping differs between TCG and KVM"
Link: http://mid.mail-archive.com/aaedee84-d3ed-a4f9-21e7-d221a28d1683@redhat.com
Link: https://lists.gnu.org/archive/html/qemu-devel/2023-01/msg00199.html
Reported-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230105161804.82486-1-lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2023-01-08 01:54:23 -05:00
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audio qapi audio: Elide redundant has_FOO in generated C 2022-12-13 18:31:37 +01:00
authz configure, meson: convert pam detection to meson 2021-06-25 10:54:10 +02:00
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bsd-user Drop more useless casts from void * to pointer 2022-12-14 16:19:35 +01:00
chardev qapi chardev: Elide redundant has_FOO in generated C 2022-12-14 20:04:47 +01:00
common-user common-user: Only compile the common user code if have_user is set 2022-06-28 11:12:05 +02:00
configs i386, mips: Resolve redundant ACPI and APM dependencies 2023-01-08 01:54:21 -05:00
contrib contrib/vhost-user-blk: Replace lseek64 with lseek 2022-12-21 07:32:24 -05:00
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disas disas/nanomips: Tidy read for 48-bit opcodes 2022-11-08 01:04:25 +01:00
docs docs/devel: Rules on #include in headers 2023-01-08 01:54:22 -05:00
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gdb-xml gdb-xml: Fix size of EFER register on i386 architecture when debugged by GDB 2022-11-06 09:48:26 +01:00
gdbstub gdbstub: move guest debug support check to ops 2022-10-06 11:53:41 +01:00
hw acpi: cpuhp: fix guest-visible maximum access size to the legacy reg block 2023-01-08 01:54:23 -05:00
include hw/acpi/aml-build: Only generate cluster node in PPTT when specified 2023-01-08 01:54:23 -05:00
io io/channel-watch: Fix socket watch on Windows 2022-10-26 13:32:08 +01:00
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meson@3a9b285a55 meson: require 0.61.3 2022-10-01 21:16:36 +02:00
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scsi QIOChannel: Add flags on io_writev and introduce io_flush callback 2022-05-16 13:56:24 +01:00
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storage-daemon qsd: Unlink absolute PID file path 2022-07-12 14:30:38 +02:00
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subprojects libvhost-user: Switch to unsigned int for inuse field in struct VuVirtq 2022-12-21 07:32:24 -05:00
target First RISC-V PR for QEMU 8.0 2023-01-06 22:15:53 +00:00
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tests tests: acpi: aarch64: Add *.topology tables 2023-01-08 01:54:23 -05:00
tools cleanup: Tweak and re-run return_directly.cocci 2022-12-14 16:19:35 +01:00
trace include/hw/core: Create struct CPUJumpCache 2022-10-04 12:13:12 -07:00
ui include/hw/pci: Split pci_device.h off pci.h 2023-01-08 01:54:22 -05:00
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.dir-locals.el Add .dir-locals.el file to configure emacs coding style 2015-10-08 19:46:01 +03:00
.editorconfig .editorconfig: update the automatic mode setting for Emacs 2021-03-10 15:34:11 +00:00
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.travis.yml Revert "gitlab: disable accelerated zlib for s390x" 2022-07-20 12:15:09 +01:00
block.c block: GRAPH_RDLOCK for functions only called by co_wrappers 2022-12-15 16:08:23 +01:00
blockdev-nbd.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
blockdev.c block: Fix locking in external_snapshot_prepare() 2022-12-15 16:08:23 +01:00
blockjob.c block: Remove drained_end_counter 2022-12-15 16:07:42 +01:00
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COPYING.LIB COPYING.LIB: Synchronize the LGPL 2.1 with the version from gnu.org 2019-01-30 11:01:22 +01:00
cpu.c accel/tcg: Complete cpu initialization before registration 2022-11-01 08:31:41 +11:00
cpus-common.c cpus: Introduce cpu_list_generation_id 2022-07-20 12:15:08 +01:00
disas.c disas: use result of ->read_memory_func 2022-10-06 11:53:40 +01:00
event-loop-base.c util/event-loop-base: Introduce options to set the thread pool size 2022-05-09 10:43:23 +01:00
gitdm.config contrib/gitdm: add a new interns group-map for GSoC/Outreachy work 2021-07-23 17:22:16 +01:00
hmp-commands-info.hx hmp: add virtio commands 2022-10-09 16:38:45 -04:00
hmp-commands.hx qapi: net: add stream and dgram netdevs 2022-10-28 13:28:52 +08:00
iothread.c error: Move ERRP_GUARD() to the beginning of the function 2022-12-14 16:19:35 +01:00
job-qmp.c qapi job: Elide redundant has_FOO in generated C 2022-12-14 20:04:47 +01:00
job.c block: remove bdrv_try_set_aio_context and replace it with bdrv_try_change_aio_context 2022-10-27 20:14:11 +02:00
Kconfig meson: Introduce target-specific Kconfig 2021-07-09 18:21:34 +02:00
Kconfig.host vfio-user: build library 2022-06-15 16:42:33 +01:00
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MAINTAINERS testing updates: 2023-01-04 16:47:37 +00:00
Makefile configure: cleanup creation of tests/tcg target config 2022-10-06 11:53:40 +01:00
memory_ldst.c.inc exec/memory_ldst: Use correct type sizes 2021-05-26 08:35:51 -07:00
meson_options.txt target/hexagon: prepare input for the idef-parser 2022-12-16 11:36:50 -08:00
meson.build Fix race conditions in new user-only vma tracking. 2023-01-06 15:40:37 +00:00
module-common.c all: Clean up includes 2016-02-04 17:41:30 +00:00
os-posix.c os-posix: asynchronous teardown for shutdown on Linux 2022-10-31 09:46:34 +01:00
os-win32.c Remove qemu-common.h include from most units 2022-04-06 14:31:55 +02:00
page-vary-common.c Remove qemu-common.h include from most units 2022-04-06 14:31:55 +02:00
page-vary.c include: move target page bits declaration to page-vary.h 2022-04-06 14:31:43 +02:00
qemu-bridge-helper.c qemu-bridge-helper: relocate path to default ACL 2020-09-30 19:11:36 +02:00
qemu-edid.c qemu-edid: Restrict input parameter -d to avoid division by zero 2022-10-12 13:38:15 +02:00
qemu-img-cmds.hx qemu-img: Unify [-b [-F]] documentation 2022-02-01 13:49:15 +01:00
qemu-img.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
qemu-io-cmds.c block: Change blk_pwrite_compressed() param order 2022-07-12 12:14:56 +02:00
qemu-io.c include: move qemu_*_exec_dir() to cutils 2022-05-28 11:42:56 +02:00
qemu-keymap.c qemu-keymap: Add license in generated files 2021-12-17 10:41:50 +01:00
qemu-nbd.c qapi block: Elide redundant has_FOO in generated C 2022-12-14 20:03:25 +01:00
qemu-options.hx hw/acpi/aml-build: Only generate cluster node in PPTT when specified 2023-01-08 01:54:23 -05:00
qemu.nsi nsis installer: Fix mouse-over descriptions for emulators 2022-03-18 10:55:15 +00:00
qemu.sasl sasl: remove comment about obsolete kerberos versions 2021-06-14 13:28:50 +01:00
README.rst README.rst: fix link formatting 2022-08-04 13:44:21 +02:00
replication.c replication: move include out of root directory 2021-05-26 14:49:46 +02:00
trace-events accel/tcg: Remove trace events from trace-root.h 2022-12-20 17:11:12 -08:00
VERSION Open 8.0 development tree 2022-12-13 15:56:26 -05:00
version.rc configure: remove CONFIG_FILEVERSION and CONFIG_PRODUCTVERSION 2021-01-02 21:03:37 +01:00

===========
QEMU README
===========

QEMU is a generic and open source machine & userspace emulator and
virtualizer.

QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).

QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.

QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.

QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.


Documentation
=============

Documentation can be found hosted online at
`<https://www.qemu.org/documentation/>`_. The documentation for the
current development version that is available at
`<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/``
folder in the source tree, and is built by `Sphinx
<https://www.sphinx-doc.org/en/master/>`_.


Building
========

QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:


.. code-block:: shell

  mkdir build
  cd build
  ../configure
  make

Additional information can also be found online via the QEMU website:

* `<https://wiki.qemu.org/Hosts/Linux>`_
* `<https://wiki.qemu.org/Hosts/Mac>`_
* `<https://wiki.qemu.org/Hosts/W32>`_


Submitting patches
==================

The QEMU source code is maintained under the GIT version control system.

.. code-block:: shell

   git clone https://gitlab.com/qemu-project/qemu.git

When submitting patches, one common approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the `style section
<https://www.qemu.org/docs/master/devel/style.html>`_ of
the Developers Guide.

Additional information on submitting patches can be found online via
the QEMU website

* `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_
* `<https://wiki.qemu.org/Contribute/TrivialPatches>`_

The QEMU website is also maintained under source control.

.. code-block:: shell

  git clone https://gitlab.com/qemu-project/qemu-web.git

* `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_

A 'git-publish' utility was created to make above process less
cumbersome, and is highly recommended for making regular contributions,
or even just for sending consecutive patch series revisions. It also
requires a working 'git send-email' setup, and by default doesn't
automate everything, so you may want to go through the above steps
manually for once.

For installation instructions, please go to

*  `<https://github.com/stefanha/git-publish>`_

The workflow with 'git-publish' is:

.. code-block:: shell

  $ git checkout master -b my-feature
  $ # work on new commits, add your 'Signed-off-by' lines to each
  $ git publish

Your patch series will be sent and tagged as my-feature-v1 if you need to refer
back to it in the future.

Sending v2:

.. code-block:: shell

  $ git checkout my-feature # same topic branch
  $ # making changes to the commits (using 'git rebase', for example)
  $ git publish

Your patch series will be sent with 'v2' tag in the subject and the git tip
will be tagged as my-feature-v2.

Bug reporting
=============

The QEMU project uses GitLab issues to track bugs. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:

* `<https://gitlab.com/qemu-project/qemu/-/issues>`_

If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via GitLab.

For additional information on bug reporting consult:

* `<https://wiki.qemu.org/Contribute/ReportABug>`_


ChangeLog
=========

For version history and release notes, please visit
`<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for
more detailed information.


Contact
=======

The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC

* `<mailto:qemu-devel@nongnu.org>`_
* `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_
* #qemu on irc.oftc.net

Information on additional methods of contacting the community can be
found online via the QEMU website:

* `<https://wiki.qemu.org/Contribute/StartHere>`_