linux-kernel - Re: [PATCH v2 06/45] KVM: arm64: Make MPAMSM

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Message-ID: <a984edef-10e6-4977-a939-6299e37d8ef1@arm.com>
Date: Mon, 5 Jan 2026 16:57:09 +0000
From: Ben Horgan <ben.horgan@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com,
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 fenghuay@...dia.com, gshan@...hat.com, james.morse@....com,
 kobak@...dia.com, lcherian@...vell.com,
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 peternewman@...gle.com, punit.agrawal@....qualcomm.com,
 quic_jiles@...cinc.com, reinette.chatre@...el.com, rohit.mathew@....com,
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 joey.gouly@....com, suzuki.poulose@....com, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v2 06/45] KVM: arm64: Make MPAMSM_EL1 accesses UNDEF

Hi Jonathan,

On 1/5/26 16:47, Jonathan Cameron wrote:
> On Fri, 19 Dec 2025 18:11:08 +0000
> Ben Horgan <ben.horgan@....com> wrote:
> 
>> The MPAMSM_EL1 controls the MPAM labeling for an SMCU, Streaming Mode
>> Compute Unit. As there is on MPAM support in kvm, make sure MPAMSM_EL1
>> accesses trigger an UNDEF.
>>
>> The range of valid configurations for the PARTID and PMG in MPAMSM_EL1 is
>> not currently specified in Arm Architectural Reference Manual but the
>> architect has confirmed that it is intended to be the same as that for the
>> cpu configuration in the MPAMy_ELx registers.
> 
> Good to know but I'm not seeing why it matters in this patch. Perhaps
> a little more on that?

Hmmm, yes. This paragraph should go with patch 11 where we start setting
MPAMSM_EL1 with the same value as MPAM0_EL1 and MPAM1_EL1.

> 
>>
>> Signed-off-by: Ben Horgan <ben.horgan@....com>
> 
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> 
>> ---
>>  arch/arm64/kvm/sys_regs.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index c8fd7c6a12a1..72654ab984ee 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -3373,6 +3373,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>>  
>>  	{ SYS_DESC(SYS_MPAM1_EL1), undef_access },
>>  	{ SYS_DESC(SYS_MPAM0_EL1), undef_access },
>> +	{ SYS_DESC(SYS_MPAMSM_EL1), undef_access },
>> +
>>  	{ SYS_DESC(SYS_VBAR_EL1), access_rw, reset_val, VBAR_EL1, 0 },
>>  	{ SYS_DESC(SYS_DISR_EL1), NULL, reset_val, DISR_EL1, 0 },
>>  
> 

Thanks,

Ben