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acpi: Add machine option to disable SPCR table

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The ACPI SPCR (Serial Port Console Redirection) table allows firmware
to specify a preferred serial console device to the operating system.
On ARM64 systems, Linux by default respects this table: even if the
kernel command line does not include a hardware serial console (e.g.,
"console=ttyAMA0"), the kernel still register the serial device
referenced by SPCR as a printk console.

While this behavior is standard-compliant, it can lead to situations
where guest console behavior is influenced by platform firmware rather
than user-specified configuration. To make guest console behavior more
predictable and under user control, this patch introduces a machine
option to explicitly disable SPCR table exposure:

    -machine spcr=off

By default, the option is enabled (spcr=on), preserving existing
behavior. When disabled, QEMU will omit the SPCR table from the guest's
ACPI namespace, ensuring that only consoles explicitly declared in the
kernel command line are registered.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Message-Id: <20250528105404.457729-2-me@linux.beauty>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Li Chen 2025-05-28 18:53:35 +08:00 • committed by Michael S. Tsirkin
parent 5788929e05
commit 54401d5abd
6 changed files with 39 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

5
hw/arm/virt-acpi-build.c
View file

@ -1023,7 +1023,10 @@ void virt_acpi_build(VirtMachineState *vms, AcpiBuildTables *tables)
}
acpi_add_table(table_offsets, tables_blob);
spcr_setup(tables_blob, tables->linker, vms);
if (ms->acpi_spcr_enabled) {
spcr_setup(tables_blob, tables->linker, vms);
}
acpi_add_table(table_offsets, tables_blob);
build_dbg2(tables_blob, tables->linker, vms);

22
hw/core/machine.c
View file

@ -577,6 +577,20 @@ static void machine_set_nvdimm(Object *obj, bool value, Error **errp)
ms->nvdimms_state->is_enabled = value;
}
static bool machine_get_spcr(Object *obj, Error **errp)
{
MachineState *ms = MACHINE(obj);
return ms->acpi_spcr_enabled;
}
static void machine_set_spcr(Object *obj, bool value, Error **errp)
{
MachineState *ms = MACHINE(obj);
ms->acpi_spcr_enabled = value;
}
static bool machine_get_hmat(Object *obj, Error **errp)
{
MachineState *ms = MACHINE(obj);
@ -1281,6 +1295,14 @@ static void machine_initfn(Object *obj)
"Table (HMAT)");
}
/* SPCR */
ms->acpi_spcr_enabled = true;
object_property_add_bool(obj, "spcr", machine_get_spcr, machine_set_spcr);
object_property_set_description(obj, "spcr",
"Set on/off to enable/disable "
"ACPI Serial Port Console Redirection "
"Table (spcr)");
/* default to mc->default_cpus */
ms->smp.cpus = mc->default_cpus;
ms->smp.max_cpus = mc->default_cpus;

4
hw/loongarch/virt-acpi-build.c
View file

@ -557,7 +557,9 @@ static void acpi_build(AcpiBuildTables *tables, MachineState *machine)
acpi_add_table(table_offsets, tables_blob);
build_srat(tables_blob, tables->linker, machine);
acpi_add_table(table_offsets, tables_blob);
spcr_setup(tables_blob, tables->linker, machine);
if (machine->acpi_spcr_enabled)
spcr_setup(tables_blob, tables->linker, machine);
if (machine->numa_state->num_nodes) {
if (machine->numa_state->have_numa_distance) {

5
hw/riscv/virt-acpi-build.c
View file

@ -894,7 +894,10 @@ static void virt_acpi_build(RISCVVirtState *s, AcpiBuildTables *tables)
}
acpi_add_table(table_offsets, tables_blob);
spcr_setup(tables_blob, tables->linker, s);
if (ms->acpi_spcr_enabled) {
spcr_setup(tables_blob, tables->linker, s);
}
acpi_add_table(table_offsets, tables_blob);
{

1
include/hw/boards.h
View file

@ -443,6 +443,7 @@ struct MachineState {
SmpCache smp_cache;
struct NVDIMMState *nvdimms_state;
struct NumaState *numa_state;
bool acpi_spcr_enabled;
};
/*

5
qemu-options.hx
View file

@ -38,6 +38,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
" nvdimm=on|off controls NVDIMM support (default=off)\n"
" memory-encryption=@var{} memory encryption object to use (default=none)\n"
" hmat=on|off controls ACPI HMAT support (default=off)\n"
" spcr=on|off controls ACPI SPCR support (default=on)\n"
#ifdef CONFIG_POSIX
" aux-ram-share=on|off allocate auxiliary guest RAM as shared (default: off)\n"
#endif
@ -105,6 +106,10 @@ SRST
Enables or disables ACPI Heterogeneous Memory Attribute Table
(HMAT) support. The default is off.
``spcr=on|off``
Enables or disables ACPI Serial Port Console Redirection Table
(SPCR) support. The default is on.
``aux-ram-share=on|off``
Allocate auxiliary guest RAM as an anonymous file that is
shareable with an external process. This option applies to