[v3] arm_mpam: Add KVM/arm64 and resctrl glue code

[PATCH v3 08/47] arm64: mpam: Advertise the CPUs MPAM limits to the driver

Posted by Ben Horgan 4 weeks ago

From: James Morse <james.morse@arm.com>

Requestors need to populate the MPAM fields for any traffic they send on
the interconnect. For the CPUs these values are taken from the
corresponding MPAMy_ELx register. Each requestor may have a limit on the
largest PARTID or PMG value that can be used. The MPAM driver has to
determine the system-wide minimum supported PARTID and PMG values.

To do this, the driver needs to be told what each requestor's limit is.

CPUs are special, but this infrastructure is also needed for the SMMU and
GIC ITS. Call the helper to tell the MPAM driver what the CPUs can do.

The return value can be ignored by the arch code as it runs well before the
MPAM driver starts probing.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
 arch/arm64/kernel/mpam.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
index 9866d2ca0faa..e6feff2324ac 100644
--- a/arch/arm64/kernel/mpam.c
+++ b/arch/arm64/kernel/mpam.c
@@ -3,6 +3,7 @@
 
 #include <asm/mpam.h>
 
+#include <linux/arm_mpam.h>
 #include <linux/jump_label.h>
 #include <linux/percpu.h>
 
@@ -11,3 +12,14 @@ DEFINE_PER_CPU(u64, arm64_mpam_default);
 DEFINE_PER_CPU(u64, arm64_mpam_current);
 
 u64 arm64_mpam_global_default;
+
+static int __init arm64_mpam_register_cpus(void)
+{
+	u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
+	u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
+	u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);
+
+	return mpam_register_requestor(partid_max, pmg_max);
+}
+/* Must occur before mpam_msc_driver_init() from subsys_initcall() */
+arch_initcall(arm64_mpam_register_cpus)
-- 
2.43.0

Re: [PATCH v3 08/47] arm64: mpam: Advertise the CPUs MPAM limits to the driver

Posted by Gavin Shan 3 weeks ago

Hi Ben,

On 1/13/26 12:58 AM, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
> 
> Requestors need to populate the MPAM fields for any traffic they send on
> the interconnect. For the CPUs these values are taken from the
> corresponding MPAMy_ELx register. Each requestor may have a limit on the
> largest PARTID or PMG value that can be used. The MPAM driver has to
> determine the system-wide minimum supported PARTID and PMG values.
> 
> To do this, the driver needs to be told what each requestor's limit is.
> 
> CPUs are special, but this infrastructure is also needed for the SMMU and
> GIC ITS. Call the helper to tell the MPAM driver what the CPUs can do.
> 
> The return value can be ignored by the arch code as it runs well before the
> MPAM driver starts probing.
> 
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
>   arch/arm64/kernel/mpam.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
> index 9866d2ca0faa..e6feff2324ac 100644
> --- a/arch/arm64/kernel/mpam.c
> +++ b/arch/arm64/kernel/mpam.c
> @@ -3,6 +3,7 @@
>   
>   #include <asm/mpam.h>
>   
> +#include <linux/arm_mpam.h>
>   #include <linux/jump_label.h>
>   #include <linux/percpu.h>
>   
> @@ -11,3 +12,14 @@ DEFINE_PER_CPU(u64, arm64_mpam_default);
>   DEFINE_PER_CPU(u64, arm64_mpam_current);
>   
>   u64 arm64_mpam_global_default;
> +
> +static int __init arm64_mpam_register_cpus(void)
> +{
> +	u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
> +	u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
> +	u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);
> +
> +	return mpam_register_requestor(partid_max, pmg_max);

mpam_register_requestor() is exposed until CONFIG_ARM64_MPAM_DRIVER is set.
CONFIG_ARM64_MPAM_DRIVER and CONFIG_ARM64_MPAM can be different until PATCH[39/47]
is applied. So we need PATCH[39/47] to be applied prior to this patch so that
mpam_register_requestor() is always existing and exposed.

> +}
> +/* Must occur before mpam_msc_driver_init() from subsys_initcall() */
> +arch_initcall(arm64_mpam_register_cpus)

Thanks,
Gavin

Re: [PATCH v3 08/47] arm64: mpam: Advertise the CPUs MPAM limits to the driver

Posted by Ben Horgan 3 weeks ago

Hi Gavin,

On 1/19/26 06:37, Gavin Shan wrote:
> Hi Ben,
> 
> On 1/13/26 12:58 AM, Ben Horgan wrote:
>> From: James Morse <james.morse@arm.com>
>>
>> Requestors need to populate the MPAM fields for any traffic they send on
>> the interconnect. For the CPUs these values are taken from the
>> corresponding MPAMy_ELx register. Each requestor may have a limit on the
>> largest PARTID or PMG value that can be used. The MPAM driver has to
>> determine the system-wide minimum supported PARTID and PMG values.
>>
>> To do this, the driver needs to be told what each requestor's limit is.
>>
>> CPUs are special, but this infrastructure is also needed for the SMMU and
>> GIC ITS. Call the helper to tell the MPAM driver what the CPUs can do.
>>
>> The return value can be ignored by the arch code as it runs well
>> before the
>> MPAM driver starts probing.
>>
>> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
>> Signed-off-by: James Morse <james.morse@arm.com>
>> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
>> ---
>>   arch/arm64/kernel/mpam.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
>> index 9866d2ca0faa..e6feff2324ac 100644
>> --- a/arch/arm64/kernel/mpam.c
>> +++ b/arch/arm64/kernel/mpam.c
>> @@ -3,6 +3,7 @@
>>     #include <asm/mpam.h>
>>   +#include <linux/arm_mpam.h>
>>   #include <linux/jump_label.h>
>>   #include <linux/percpu.h>
>>   @@ -11,3 +12,14 @@ DEFINE_PER_CPU(u64, arm64_mpam_default);
>>   DEFINE_PER_CPU(u64, arm64_mpam_current);
>>     u64 arm64_mpam_global_default;
>> +
>> +static int __init arm64_mpam_register_cpus(void)
>> +{
>> +    u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
>> +    u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
>> +    u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);
>> +
>> +    return mpam_register_requestor(partid_max, pmg_max);
> 
> mpam_register_requestor() is exposed until CONFIG_ARM64_MPAM_DRIVER is set.
> CONFIG_ARM64_MPAM_DRIVER and CONFIG_ARM64_MPAM can be different until
> PATCH[39/47]
> is applied. So we need PATCH[39/47] to be applied prior to this patch so
> that
> mpam_register_requestor() is always existing and exposed.

I've split out the part of PATCH[39/47] that removes the CONFIG_EXPERT
restriction and put it before this patch. With that CONFIG_ARM64_MPAM
will unconditionally select CONFIG_ARM64_MPAM_DRIVER.

> 
>> +}
>> +/* Must occur before mpam_msc_driver_init() from subsys_initcall() */
>> +arch_initcall(arm64_mpam_register_cpus)
> 
> Thanks,
> Gavin
> 
Thanks,

Ben

Re: [PATCH v3 08/47] arm64: mpam: Advertise the CPUs MPAM limits to the driver

Posted by Catalin Marinas 3 weeks, 4 days ago

On Mon, Jan 12, 2026 at 04:58:35PM +0000, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
> 
> Requestors need to populate the MPAM fields for any traffic they send on
> the interconnect. For the CPUs these values are taken from the
> corresponding MPAMy_ELx register. Each requestor may have a limit on the
> largest PARTID or PMG value that can be used. The MPAM driver has to
> determine the system-wide minimum supported PARTID and PMG values.
> 
> To do this, the driver needs to be told what each requestor's limit is.
> 
> CPUs are special, but this infrastructure is also needed for the SMMU and
> GIC ITS. Call the helper to tell the MPAM driver what the CPUs can do.
> 
> The return value can be ignored by the arch code as it runs well before the
> MPAM driver starts probing.
> 
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>