linux-kernel - Re: [PATCH v5 14/34] arm_mpam: Probe hardware to find the supported partid/pmg values

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Message-ID: <d555d2e8-2bc8-4be8-af13-3dc3ffe9b8ca@nvidia.com>
Date: Tue, 18 Nov 2025 08:23:59 -0800
From: Fenghua Yu <fenghuay@...dia.com>
To: Ben Horgan <ben.horgan@....com>, james.morse@....com
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, bobo.shaobowang@...wei.com,
 carl@...amperecomputing.com, catalin.marinas@....com, dakr@...nel.org,
 dave.martin@....com, david@...hat.com, dfustini@...libre.com,
 gregkh@...uxfoundation.org, gshan@...hat.com, guohanjun@...wei.com,
 jeremy.linton@....com, jonathan.cameron@...wei.com, kobak@...dia.com,
 lcherian@...vell.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 lpieralisi@...nel.org, peternewman@...gle.com, quic_jiles@...cinc.com,
 rafael@...nel.org, robh@...nel.org, rohit.mathew@....com,
 scott@...amperecomputing.com, sdonthineni@...dia.com, sudeep.holla@....com,
 tan.shaopeng@...itsu.com, will@...nel.org, xhao@...ux.alibaba.com,
 Shaopeng Tan <tan.shaopeng@...fujitsu.com>, Zeng Heng <zengheng4@...wei.com>
Subject: Re: [PATCH v5 14/34] arm_mpam: Probe hardware to find the supported
 partid/pmg values



On 11/17/25 08:59, Ben Horgan wrote:
> From: James Morse <james.morse@....com>
> 
> 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.
> 
> This adds the low level MSC write accessors.
> 
> 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>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Tested-by: Carl Worth <carl@...amperecomputing.com>
> Tested-by: Gavin Shan <gshan@...hat.com>
> Tested-by: Zeng Heng <zengheng4@...wei.com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>
> ---
> Changes since v3:
>  From Jonathan:
> Stray comma in printk
> Unnecessary braces
> ---
>   drivers/resctrl/mpam_devices.c  | 148 +++++++++++++++++++++++++++++++-
>   drivers/resctrl/mpam_internal.h |   6 ++
>   include/linux/arm_mpam.h        |  14 +++
>   3 files changed, 167 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 51284f55ae9b..ac1c770cea35 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -6,6 +6,7 @@
>   #include <linux/acpi.h>
>   #include <linux/atomic.h>
>   #include <linux/arm_mpam.h>
> +#include <linux/bitfield.h>
>   #include <linux/cacheinfo.h>
>   #include <linux/cpu.h>
>   #include <linux/cpumask.h>
> @@ -42,6 +43,15 @@ static atomic_t mpam_num_msc;
>   static int mpam_cpuhp_state;
>   static DEFINE_MUTEX(mpam_cpuhp_state_lock);
>   
> +/*
> + * The smallest common values for any CPU or MSC in the system.
> + * Generating traffic outside this range will result in screaming interrupts.
> + */
> +u16 mpam_partid_max;
> +u8 mpam_pmg_max;
> +static bool partid_max_init, partid_max_published;
> +static DEFINE_SPINLOCK(partid_max_lock);
> +
>   /*
>    * mpam is enabled once all devices have been probed from CPU online callbacks,
>    * scheduled via this work_struct. If access to an MSC depends on a CPU that
> @@ -143,6 +153,70 @@ 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);

This check may cause false warning when reg range is still valid. Need 
to change to:
+	WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz);

With this minor change,

Reviewed-by: Fenghua Yu <fenghuay@...dia.com>

[SNIP]

Thanks.

-Fenghua