linux-kernel - Re: [PATCH] arm64: cpufeature: Add support for the MPAM v0.1 architecture version

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Message-ID: <0944256a-bcc6-56fa-e3f9-eb3a83c45505@huawei.com>
Date: Wed, 28 Jan 2026 16:54:30 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: Ben Horgan <ben.horgan@....com>, <james.morse@....com>,
	<miko.lenczewski@....com>, <thuth@...hat.com>, <mark.rutland@....com>,
	<yeoreum.yun@....com>, <robh@...nel.org>, <james.clark@...aro.org>,
	<ahmed.genidi@....com>, <xry111@...111.site>, <oupton@...nel.org>,
	<lpieralisi@...nel.org>, <catalin.marinas@....com>,
	<mrigendra.chaubey@...il.com>, <suzuki.poulose@....com>, <maz@...nel.org>,
	<ardb@...nel.org>, <broonie@...nel.org>, <will@...nel.org>,
	<kevin.brodsky@....com>, <leo.yan@....com>, <anshuman.khandual@....com>,
	<yang@...amperecomputing.com>, <frederic@...nel.org>, <guohanjun@...wei.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Kefeng Wang
	<wangkefeng.wang@...wei.com>
CC: <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<leijitang@...wei.com>, "Zengtao (B)" <prime.zeng@...ilicon.com>
Subject: Re: [PATCH] arm64: cpufeature: Add support for the MPAM v0.1
 architecture version



On 2026/1/27 22:30, Ben Horgan wrote:
> Hi Zeng,
> 
> On 1/4/26 13:34, Zeng Heng wrote:
>> According to the MPAM spec [1], the supported architecture versions are
>> v1.0, v1.1 and v0.1. MPAM versions v0.1 and v1.1 are functionally
>> identical, but v0.1 additionally supports the FORCE_NS feature.
>>
>> ID_AA64PR | ID_AA64PR | MPAM Extension | Notes
>> F0_EL1.   | F1_EL1.   | Architecture   |
>> MPAM      | MPAM_frac | version        |
>> ---------------------------------------------------------------------------
>> 0b0000    | 0b0001    | v0.1           | MPAM v0.1 is implemented.
>>            |           |                | MPAM v0.1 is the same as MPAM v1.1
>>            |           |                | with FORCE_NS which is
>>            |           |                | incompatible with MPAM v1.0.
>> ---------------------------------------------------------------------------
>> 0b0001    | 0b0000    | v1.0           | MPAM v1.0 is implemented.
>> ---------------------------------------------------------------------------
>> 0b0001    | 0b0001    | v1.1           | MPAM v1.1 is implemented.
>>            |           |                | MPAM v1.1 includes all features of
>>            |           |                | MPAM v1.0.
>>            |           |                | It must not include FORCE_NS.
>>
>> FORCE_NS is a feature that operates in EL3 mode. Consequently, the current
>> Linux MPAM driver is also compatible with MPAM v0.1. To support v0.1, the
>> existing driver which only checks ID_AA64PFR0_EL1.MPAM for the major
>> version needs to examine ID_AA64PFR1_EL1.MPAM_frac for the minor version
>> as well.
>>
>> [1] https://developer.arm.com/documentation/ddi0598/db/?lang=en
>>
>> Signed-off-by: Zeng Heng <zengheng4@...wei.com>
> So far we've avoided added MPAM 0.1 support as we don't know of any
> machines using it. What's your motivation here? Do you have a machine
> with MPAM 0.1 that runs mainline linux?
> 

Thank you for your questions and for reviewing this proposal.

Regarding your inquiry about hardware usage and motivation:

Our KunPeng 920C chip (and numerous legacy SoCs in the same family)
indeed implement MPAM v0.1 extensions. These are widely deployed in
server and embedded equipment. More importantly, the product roadmap for
these platforms explicitly includes migration to mainline Linux kernels
MPAM driver for long-term support, making upstream MPAM v0.1 driver
support is a critical requirement.

In the other hand, MPAM v0.1 extension version is formally documented in
the ARM MPAM architecture specification (still included in the newest
ARM DDI 0598D.b version). The specification explicitly defines v0.1 as a
valid implementation for earlier hardware. Supporting documented
architectural features is essential for the goal of hardware
compatibility.

About technical compatibility, the MPAM v0.1 is designed as a
functionally compatible extension with the existing MPAM driver
framework. After having tested this on actual Kunpeng 920C hardware
and other MPAM v1.0 platforms running mainline kernels, this ensures
zero regression risk for v1.0/v1.1 users.


Best regards,
Zeng Heng