diff options
| author | Xiaoyao Li <xiaoyao.li@intel.com> | 2024-04-03 10:59:53 -0400 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2024-04-15 06:50:58 -0400 |
| commit | c44d44d76d443884b77bebef39cba74b89803401 (patch) | |
| tree | 11e5aed24c32ae53ed4b84ef8d7b1ad5106738e1 | |
| parent | 9fc5d5b3903f6f982801320f376146a2f8b4d0f6 (diff) | |
| download | qemu-next.tar.gz | |
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.
To detect:
When booting a VM with "-machine xx,pic=off", there is supposed to be no PIC
for the guest. When guest probes PIC, it should find nothing and log of below
should be printed:
[ 0.155970] Using NULL legacy PIC
However, the fact is that no such log printed in guest kernel, with the VM
created with "pic=off". This is because guest think there is a present due to
pcat_compat is reporte as 1 in MADT. See Linux code of probe_8259A() in
arch/x86/kernel/i8259.c
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20240403145953.3082491-1-xiaoyao.li@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
| -rw-r--r-- | hw/i386/acpi-common.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/hw/i386/acpi-common.c b/hw/i386/acpi-common.c index 20f19269da4..0cc2919bb85 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); |