From: Li Chen <chenl311@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 <chenl311@chinatelecom.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
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 63c6ef93d2..d56f44f4e8 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -590,6 +590,20 @@ 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);
@@ -1294,6 +1308,14 @@ 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 f22b2e7fc7..cdf2791a50 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
--
2.49.0On 4/22/25 10:05 PM, Li Chen wrote:
> From: Li Chen <chenl311@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 <chenl311@chinatelecom.cn>
> Reviewed-by: Bibo Mao <maobibo@loongson.cn>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>
> 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(-)
>
One coding style issue below. With it fixed:
Reviewed-by: Gavin Shan <gshan@redhat.com>
> 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 63c6ef93d2..d56f44f4e8 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -590,6 +590,20 @@ 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);
> @@ -1294,6 +1308,14 @@ 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->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 f22b2e7fc7..cdf2791a50 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
Thanks,
Gavin
Hi Gavin, ---- On Wed, 23 Apr 2025 08:11:24 +0800 Gavin Shan <gshan@redhat.com> wrote --- > On 4/22/25 10:05 PM, Li Chen wrote: > > From: Li Chen <chenl311@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 <chenl311@chinatelecom.cn> > > Reviewed-by: Bibo Mao <maobibo@loongson.cn> > > Acked-by: Michael S. Tsirkin <mst@redhat.com> > > --- > > > > 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(-) > > > > One coding style issue below. With it fixed: > > Reviewed-by: Gavin Shan <gshan@redhat.com> Thanks for your catch! I would fix it in the next version. Regards, Li
Hi,
On 22/4/25 14:05, Li Chen wrote:
> From: Li Chen <chenl311@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 <chenl311@chinatelecom.cn>
> Reviewed-by: Bibo Mao <maobibo@loongson.cn>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>
> 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/include/hw/boards.h b/include/hw/boards.h
> index f22b2e7fc7..cdf2791a50 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;
I'm a bit reluctant to add a field used by 3 virt machines as
generic in MachineState. Shouldn't it be for each machine state?
Also I'm surprised we announce the SPCR table regardless a virt
serial exists. Shouldn't we have a disabled default and only
enable on virt machines, preferably checking the serial port
availability?
> };
>
> /*
> 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.
Hi Philippe Mathieu-Daudé,
Thanks for your review!
---- On Tue, 22 Apr 2025 21:18:46 +0800 Philippe Mathieu-Daudé <philmd@linaro.org> wrote ---
> Hi,
>
> On 22/4/25 14:05, Li Chen wrote:
> > diff --git a/include/hw/boards.h b/include/hw/boards.h
> > index f22b2e7fc7..cdf2791a50 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;
>
> I'm a bit reluctant to add a field used by 3 virt machines as
> generic in MachineState. Shouldn't it be for each machine state?
I looked for alternative locations for this field before submitting v1 but couldn't find any.
I re-evaluated potential locations, like struct AcpiBuildState, but ARM, LoongArch, and RISC-V
just use their own AcpiBuildState.
BTW, ACPI-supporting virtual machines may eventually adopt SPCR. Although current there
are just three users, future adoption is probable, making it a suitable field for each machine state.
Feel free to tell me if you have any other suggestions.
>
> Also I'm surprised we announce the SPCR table regardless a virt
> serial exists. Shouldn't we have a disabled default and only
> enable on virt machines, preferably checking the serial port
> availability?
So you mean we should avoid building SPCR for cases like "-serial none"? If so, I can add a patch to check serial
device availability before doing spcr_setup in ARM/RISC-V/LoongArch codes.
Should this change be the first patch in this series, or just a separate series?
Regards,
Li
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