linux-kernel - Re: [PATCH v2 15/29] arm_mpam: Reset MSC controls from cpu hp callbacks

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Message-ID: <72750912-ed50-4a1b-8c43-455a7bc9efc1@arm.com>
Date: Fri, 17 Oct 2025 19:50:46 +0100
From: James Morse <james.morse@....com>
To: Fenghua Yu <fenghuay@...dia.com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 baisheng.gao@...soc.com, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Rob Herring <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 15/29] arm_mpam: Reset MSC controls from cpu hp
 callbacks

Hi Fenghua,

On 05/10/2025 21:43, Fenghua Yu wrote:
> Hi, James,
> 
> On 9/10/25 13:42, James Morse wrote:
>> When a CPU comes online, it may bring a newly accessible MSC with
>> it. Only the default partid has its value reset by hardware, and
>> even then the MSC might not have been reset since its config was
>> previously dirtyied. e.g. Kexec.
> 
> typo: s/dirtyied/dirtied/
> 
> 
>>
>> Any in-use partid must have its configuration restored, or reset.
>> In-use partids may be held in caches and evicted later.
>>
>> MSC are also reset when CPUs are taken offline to cover cases where
>> firmware doesn't reset the MSC over reboot using UEFI, or kexec
>> where there is no firmware involvement.
>>
>> If the configuration for a RIS has not been touched since it was
>> brought online, it does not need resetting again.
>>
>> To reset, write the maximum values for all discovered controls.
>>
>> CC: Rohit Mathew<Rohit.Mathew@....com>
>> Signed-off-by: James Morse<james.morse@....com>
> 
> Other than the minor comments,
> 
> Reviewed-by: Fenghua Yu <fenghuay@...dia.com>

Thanks,


> [SNIP]
>> +static void mpam_reset_ris(struct mpam_msc_ris *ris)
>> +{
>> +    u16 partid, partid_max;
>> +
>> +    mpam_assert_srcu_read_lock_held();
>> +
>> +    if (ris->in_reset_state)
>> +        return;
>> +
>> +    spin_lock(&partid_max_lock);
>> +    partid_max = mpam_partid_max;
>> +    spin_unlock(&partid_max_lock);
>> +    for (partid = 0; partid < partid_max; partid++)
> 
>  * Should partid_max be inclusive? So it's "partid < partid_max + 1" here?
> 
> MPAM spec says max PARTID is inclusive: "The range of valid PARTIDs is 0 to the maximum
> PARTID, inclusive. The maximum values of a PARTID implemented by different MSCs need not
> be the same".

Hmmm, if partid_max is 0 then this loop should run only once, so yet.


Thanks,

James