Re: [PATCH v2] hw/i386/acpi: Set PCAT_COMPAT bit only when pic is not disabled

[Igor Mammedov]

On Wed,  3 Apr 2024 10:59:53 -0400
Xiaoyao Li <xiaoyao.li@intel.com> wrote:

> A value 1 of PCAT_COMPAT (bit 0) of MADT.Flags indicates that the system
> also has a PC-AT-compatible dual-8259 setup, i.e., the PIC.
> 
> When PIC is not enabled (pic=off) for x86 machine, the PCAT_COMPAT bit
> needs to be cleared. Otherwise, the guest thinks there is a present PIC.

Can you add to commit message reproducer (aka qemu CLI and relevant
logs/symptoms observed on guest side)?

> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> changes in v2:
> - Clarify more in commit message;
> ---
>  hw/i386/acpi-common.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i386/acpi-common.c b/hw/i386/acpi-common.c
> index 20f19269da40..0cc2919bb851 100644
> --- a/hw/i386/acpi-common.c
> +++ b/hw/i386/acpi-common.c
> @@ -107,7 +107,9 @@ void acpi_build_madt(GArray *table_data, BIOSLinker 
> *linker,
>      acpi_table_begin(&table, table_data);
>      /* Local APIC Address */
>      build_append_int_noprefix(table_data, APIC_DEFAULT_ADDRESS, 4);
> -    build_append_int_noprefix(table_data, 1 /* PCAT_COMPAT */, 4); /* Flags 
> */
> +    /* Flags. bit 0: PCAT_COMPAT */
> +    build_append_int_noprefix(table_data,
> +                              x86ms->pic != ON_OFF_AUTO_OFF ? 1 : 0 , 4);
>  
>      for (i = 0; i < apic_ids->len; i++) {
>          pc_madt_cpu_entry(i, apic_ids, table_data, false);