From: Li Chen <chenl...@chinatelecom.cn>
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 <chenl...@chinatelecom.cn>
Reviewed-by: Bibo Mao <maob...@loongson.cn>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Reviewed-by: Gavin Shan <gs...@redhat.com>
---
Changes since V2: Add Reviewed-by from Gavin Shan <gs...@redhat.com>
for the first patch and fix style issue.
Changes since V1: add Reviewed-by and Acked-by
hw/arm/virt-acpi-build.c | 5 ++++-
hw/core/machine.c | 22 ++++++++++++++++++++++
hw/loongarch/virt-acpi-build.c | 4 +++-
hw/riscv/virt-acpi-build.c | 5 ++++-
include/hw/boards.h | 1 +
qemu-options.hx | 5 +++++
6 files changed, 39 insertions(+), 3 deletions(-)
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 3ac8f8e178..f25c3b26ce 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -940,7 +940,10 @@ void virt_acpi_build(VirtMachineState *vms,
AcpiBuildTables *tables)
}
acpi_add_table(table_offsets, tables_blob);
- spcr_setup(tables_blob, tables->linker, vms);
+
+ if (ms->enable_spcr) {
+ spcr_setup(tables_blob, tables->linker, vms);
+ }
acpi_add_table(table_offsets, tables_blob);
build_dbg2(tables_blob, tables->linker, vms);
diff --git a/hw/core/machine.c b/hw/core/machine.c
index ed01798d37..71a935512e 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -593,6 +593,20 @@ 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->enable_spcr;
+}
+
+static void machine_set_spcr(Object *obj, bool value, Error **errp)
+{
+ MachineState *ms = MACHINE(obj);
+
+ ms->enable_spcr = value;
+}
+
static bool machine_get_hmat(Object *obj, Error **errp)
{
MachineState *ms = MACHINE(obj);
@@ -1297,6 +1311,14 @@ static void machine_initfn(Object *obj)
"Table (HMAT)");
}
+ /* SPCR */
+ ms->enable_spcr = 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;
diff --git a/hw/loongarch/virt-acpi-build.c b/hw/loongarch/virt-acpi-build.c
index fced6c445a..0e437bcf25 100644
--- a/hw/loongarch/virt-acpi-build.c
+++ b/hw/loongarch/virt-acpi-build.c
@@ -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->enable_spcr)
+ spcr_setup(tables_blob, tables->linker, machine);
if (machine->numa_state->num_nodes) {
if (machine->numa_state->have_numa_distance) {
diff --git a/hw/riscv/virt-acpi-build.c b/hw/riscv/virt-acpi-build.c
index 1ad6800508..7f6d221c63 100644
--- a/hw/riscv/virt-acpi-build.c
+++ b/hw/riscv/virt-acpi-build.c
@@ -680,7 +680,10 @@ static void virt_acpi_build(RISCVVirtState *s,
AcpiBuildTables *tables)
build_rhct(tables_blob, tables->linker, s);
acpi_add_table(table_offsets, tables_blob);
- spcr_setup(tables_blob, tables->linker, s);
+
+ if (ms->enable_spcr) {
+ spcr_setup(tables_blob, tables->linker, s);
+ }
acpi_add_table(table_offsets, tables_blob);
{
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 765dc8dd35..089104d54b 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -444,6 +444,7 @@ struct MachineState {
SmpCache smp_cache;
struct NVDIMMState *nvdimms_state;
struct NumaState *numa_state;
+ bool enable_spcr;
};
/*
diff --git a/qemu-options.hx b/qemu-options.hx
index dc694a99a3..953680595f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -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
--
2.49.0
