Re: Windows 10 won't run on default x86_64 machine anymore

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Mar 15, 2021 at 05:58:04PM +0100, Reinoud Zandijk wrote:
> Hi,
> 
> 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".


Thanks for the report!
Could you provide a bit more detail please?
Which windows version is used, which qemu command line, etc etc.

Also does this only affect pre-installed guests? what if you
install a fresh copy of windows?

> 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,
> Reinoud
> 
> 
> 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 4.8.10.1 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>
>     Message-Id:
> <500f62081626997e46f96377393d3662211763a8.1613615732.git.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(-)
> 
>