Re: [PATCH v2 00/21] Introduce ACPI watchdog for Q35 and arm/virt boards

[Igor Mammedov <imammedo@redhat.com>]

On Tue,  3 Mar 2026 10:25:11 +0100
Igor Mammedov <imammedo@redhat.com> wrote:

> Changelog:
>   v2:
>      * ditch generic '-machine acpi-watchdog' option in favor of
>        board specific variants:
>            x86/q35:  -machine wdat={on|off}
>            arm/virt: -device sbsa_gwdt,wdat={on|off}
>      * arm/virt: add FDT and GTDT ACPI entries for GWDT when it's present
>        and hide GDTD one when WDAT is enabled.
>      * arm/virt: add test case for GTDT 
>      * [18-21] optional GWDT cleanup/fixes in handling WCV register update,
>        make QEMU behave according to spec (at least the way I read it and
>        it appears MS also read it that way). It fixes Windows 11 reboots when
>        GWDT is present (without WDAT). With that fixed it's up to MS to fix
>        their driver to set sane timeout as with the current one wdatchdog
>        will never trigger.

given merge window should be open by now,
gentle ping

> Windows doesn't ship built-in TCO watchdog driver, and users are
> forced to install vendor specific driver(s) if such exists.
> However the OS provides a generic watchdog driver that uses
> ACPI WDAT table [1] to abstract actual hardware behind it.
> The same applies to ARM version of Windows.
> 
> This series adds
>  *  WDAT table tailored for TCO watchdog that Q35 already
>     has as part of ICH9 chipset and a knob to enable it.
>  *  SBSA GWDT to arm/virt machine with WDAT table tailored
>     for it and necessary tweaks to GWDT to make usable
>     with WDAT driver.
>     * in addition to WDAT, it also adds native variant
>       with GWDT described in FDT and DTDT
>       (broken on Windows/works on linux).
> 
> Guest OS WDAT support is present since Windows Vista and Linux since 2016[2].
> 
> One can test it launching VM with following options:
>   * x86:
>        -machine q35,wdat=on
>   * arm/virt:
>        -device sbsa_gwdt,wdat=on
> 
> to trace access to TCO registers one can add to CLI:
>     -trace "tco_*"
> to trace access to GWDT registers one can add to CLI:
>     -trace "sbsa_gwdt*"
> 
> To verify that guest uses WDAT (both Windows and Linux would use it if present),
>   * on linux make sure that watchdog service is configured/enabled
>     (use wdctl to check what watchdog device is in use) and then
>     trigger kernel panic with command:
>       echo c > /proc/sysrq-trigger
>   * on Windows kill svchost process, running cmd in admin mode:
>       taskkill /f /im svchost.exe
> 
> Tested with WS2025 & RHEL9.6 & Fedora 43 (aarch64)
> 
> git tree at: https://gitlab.com/imammedo/qemu/-/commits/gwdt_v2
> 
> 1) http://msdn.microsoft.com/en-us/windows/hardware/gg463320.aspx
> 2) https://lwn.net/Articles/700524/
> 
> PS:
>  previous revision:
>   https://patchew.org/QEMU/20260206131438.1857182-1-imammedo@redhat.com/
> 
> Igor Mammedov (21):
>   acpi: add API to build WDAT instructions
>   x86: q35: add 'wdat' property
>   x86: q35: generate WDAT ACPI table
>   tests: acpi: x86/q35: whitelist new WDAT table
>   tests: acpi: x86/q35: add WDAT table test case
>   tests: acpi: x86/q35: update expected WDAT blob
>   arm: sbsa_gwdt: fixup default "clock-frequency"
>   arm: add tracing events to sbsa_gwdt
>   arm: virt: create sbsa_gwdt watchdog
>   arm: sbsa_gwdt: add 'wdat' option
>   arm: virt: add support for WDAT based watchdog
>   tests: acpi: arm/virt: whitelist new WDAT table
>   tests: acpi: arm/virt: add WDAT table test case
>   tests: acpi: arm/virt: update expected WDAT blob
>   tests: acpi: arm/virt: whitelist GTDT table
>   tests: acpi: arm/virt: add GTDT watchdog table test case
>   tests: acpi: arm/virt: update expected GTDT blob
>   sbsa_gwdt: reduce code ident
>   sbsa_gwdt: move all foo_REFRESH logic under REFRESH condition
>   sbsa_gwdt: reschedule timer on direct WCV load
>   sbsa_gwdt: limit compare_value to INT64_MAX
> 
>  include/hw/acpi/wdat-gwdt.h            |  19 ++++
>  include/hw/acpi/wdat-ich9.h            |  15 ++++
>  include/hw/acpi/wdat.h                 | 118 +++++++++++++++++++++++++
>  include/hw/i386/pc.h                   |   1 +
>  include/hw/watchdog/sbsa_gwdt.h        |   1 +
>  hw/acpi/aml-build.c                    |  14 +++
>  hw/acpi/meson.build                    |   5 +-
>  hw/acpi/wdat-gwdt-stub.c               |  16 ++++
>  hw/acpi/wdat-gwdt.c                    |  92 +++++++++++++++++++
>  hw/acpi/wdat-ich9-stub.c               |  15 ++++
>  hw/acpi/wdat-ich9.c                    |  90 +++++++++++++++++++
>  hw/arm/Kconfig                         |   1 +
>  hw/arm/virt-acpi-build.c               |  65 +++++++++++++-
>  hw/arm/virt.c                          |   2 +
>  hw/core/sysbus-fdt.c                   |  32 +++++++
>  hw/i386/acpi-build.c                   |  12 +++
>  hw/i386/pc_q35.c                       |  18 ++++
>  hw/watchdog/sbsa_gwdt.c                |  65 +++++++++-----
>  hw/watchdog/trace-events               |   9 ++
>  tests/data/acpi/aarch64/virt/GTDT.gwdt | Bin 0 -> 132 bytes
>  tests/data/acpi/aarch64/virt/WDAT.wdat | Bin 0 -> 260 bytes
>  tests/data/acpi/x86/q35/WDAT.wdat      | Bin 0 -> 308 bytes
>  tests/qtest/bios-tables-test.c         |  54 +++++++++++
>  23 files changed, 618 insertions(+), 26 deletions(-)
>  create mode 100644 include/hw/acpi/wdat-gwdt.h
>  create mode 100644 include/hw/acpi/wdat-ich9.h
>  create mode 100644 include/hw/acpi/wdat.h
>  create mode 100644 hw/acpi/wdat-gwdt-stub.c
>  create mode 100644 hw/acpi/wdat-gwdt.c
>  create mode 100644 hw/acpi/wdat-ich9-stub.c
>  create mode 100644 hw/acpi/wdat-ich9.c
>  create mode 100644 tests/data/acpi/aarch64/virt/GTDT.gwdt
>  create mode 100644 tests/data/acpi/aarch64/virt/WDAT.wdat
>  create mode 100644 tests/data/acpi/x86/q35/WDAT.wdat
>