On Thu, May 15, 2025 at 08:41:03PM +0800, Li Chen wrote:
> 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.
> +
Reviewed-by: Sunil V L <suni...@ventanamicro.com>
Thanks!
Sunil
