linux-kernel - Re: [PATCH v2 11/29] arm_mpam: Probe hardware to find the supported partid/pmg values

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Message-ID: <562d1f40-4ed9-4f5b-af1b-9de45e06079e@nvidia.com>
Date: Fri, 3 Oct 2025 11:58:35 -0700
From: Fenghua Yu <fenghuay@...dia.com>
To: James Morse <james.morse@....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 11/29] arm_mpam: Probe hardware to find the supported
 partid/pmg values

Hi, James,

On 9/10/25 13:42, James Morse wrote:
> CPUs can generate traffic with a range of PARTID and PMG values,
> but each MSC may also have its own maximum size for these fields.
> Before MPAM can be used, the driver needs to probe each RIS on
> each MSC, to find the system-wide smallest value that can be used.
> The limits from requestors (e.g. CPUs) also need taking into account.
>
> While doing this, RIS entries that firmware didn't describe are created
> under MPAM_CLASS_UNKNOWN.
>
> While we're here, implement the mpam_register_requestor() call
> for the arch code to register the CPU limits. Future callers of this
> will tell us about the SMMU and ITS.
>
> Signed-off-by: James Morse <james.morse@....com>
[SNIP]
> @@ -113,6 +123,72 @@ static inline u32 _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg)
>   
>   #define mpam_read_partsel_reg(msc, reg)        _mpam_read_partsel_reg(msc, MPAMF_##reg)
>   
> +static void __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val)
> +{
> +	WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz);

if reg + 4 == msc->mapped_hwpage_sz, the register is out of boundary as 
well.

So the validation should be:

WARN_ON_ONCE(reg + sizeof(u32) >= msc->mapped_hwpage_sz);

[SNIP]

Thanks.

-Fenghua