Re: [PATCH v10 11/17] arm,x86/resctrl: Resolve INTEL_PMT_TELEMETRY symbols at runtime

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Tony,

On 7/29/26 10:27 AM, Tony Luck wrote:
> resctrl is always built-in, but INTEL_PMT_TELEMETRY and INTEL_TPMI are
> logically independent and should be loadable modules.  Switch AET to use the
> function-pointer registration API instead of direct link-time references to
> PMT symbols.
> 
> Prepare for the file system to call resctrl_arch_pre_mount() on every mount
> by moving AET enumeration into resctrl_arch_pre_mount() and cleanup into
> resctrl_arch_unmount(). This allows the PMT module to be unloaded whenever
> the filesystem is not mounted.
> 
> intel_aet_exit() was never called because resctrl is built into the kernel. All
> cleanup is now handled in the unmount path. Remove intel_aet_exit().
> 
> Note that the Linux file system code does not serialize calls to
> fs_context_operations::get_tree(), so there may be arbitrarily many parallel
> calls if users invoke mount(2) multiple times.
> 
> Zero rdt_resource::resctrl_mon::num_rmid for RDT_RESOURCE_PERF_PKG so
> that it will be re-computed next mount.
> 
> event_group::num_rmid may be reset (reduced) during enumeration. This is
> not worth resetting on unmount because the same reduction would occur on
> each subsequent mount.

I think it will be helpful to reviewers (including sashiko) to add description why
the unbalanced module reference counting is safe here.

> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---

...

> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 2c938b97b147..e335a143f3e5 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -16,10 +16,12 @@
>  
>  #define pr_fmt(fmt)	"resctrl: " fmt
>  
> +#include <linux/cleanup.h>

Following patch removing this could just be squashed here?

>  #include <linux/cpu.h>
>  #include <linux/slab.h>
>  #include <linux/err.h>
>  #include <linux/cpuhotplug.h>
> +#include <linux/mutex.h>
>  
>  #include <asm/cpu_device_id.h>
>  #include <asm/cpuid/api.h>

...

> diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
> index 407c9aba5eea..65b70cc8d0a5 100644
> --- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
> +++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c

...

> @@ -340,10 +342,22 @@ void __init intel_aet_init(void)
>  		(*peg)->num_rmid = min(max_rmid, (*peg)->num_rmid);
>  }
>  
> +/*
> + * Defend against races between module load/unload of the pmt_telemetry
> + * module and mount/unmount of the resctrl file system.

Please add to this comment what data is protected by this mutex.

> + */
> +static DEFINE_MUTEX(aet_register_lock);
> +
> +/*
> + * Track whether pmt_telemetry enumeration succeeded during mount for use during unmount.
> + */
> +static bool pmt_in_use;
Reinette