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Windows 10 won't run on default x86_64 machine anymore

From: Reinoud Zandijk
Subject: Windows 10 won't run on default x86_64 machine anymore
Date: Mon, 15 Mar 2021 17:58:04 +0100


with the introduction of the following patch from 17th of February, Win10
won't boot anymore without explicitly setting the machine to be 5.2 compatible
like pc-1440fx-5.2. The default 6.0 will cause it to panic and gives as reason
only "ACPI error".

It might work to counter a bug in Linux but this is not the place to do the
patch. The BSDs don't care and will boot fine with full ACPI regardless of the
machine chosen. Windows 10 however DOES care and gets confused.

I think its better to revert this and fix Linux ;) or make it a selectable
feature as a workaround that's by default OFF :)

With regards,

The patch concerned is:

commit 6be8cf56bc8bda2ed9a070bdb04446191f31acc9
Author: Isaku Yamahata <isaku.yamahata@intel.com>
Date:   Wed Feb 17 21:51:12 2021 -0800

    acpi/core: always set SCI_EN when SMM isn't supported
    If SMM is not supported, ACPI fixed hardware doesn't support
    legacy-mode. ACPI-only platform. Where SCI_EN in PM1_CNT register is
    always set.
    The bit tells OS legacy mode(SCI_EN cleared) or ACPI mode(SCI_EN set).
    With the next patch (setting fadt.smi_cmd = 0 when smm isn't enabled),
    guest Linux tries to switch to ACPI mode, finds smi_cmd = 0, and then
    fails to initialize acpi subsystem. This patch proactively fixes it.
    This patch changes guest ABI. To keep compatibility, use
    "smm-compat" introduced by earlier patch. If the property is true,
    disable new behavior.
    ACPI spec PM1 Event Grouping
    PM1 Eanble Registers
    > For ACPI-only platforms (where SCI_EN is always set)
    Reviewed-by: Igor Mammedov <imammedo@redhat.com>
    Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

 hw/acpi/core.c         | 11 ++++++++++-
 hw/acpi/ich9.c         |  2 +-
 hw/acpi/piix4.c        |  3 ++-
 hw/core/machine.c      |  5 ++++-
 hw/isa/vt82c686.c      |  2 +-
 include/hw/acpi/acpi.h |  4 +++-
 6 files changed, 21 insertions(+), 6 deletions(-)

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