Re: [PATCH v9 2/9] fs/resctrl: Add resctrl_arch_rmid_idx_match() helper

[Ben Horgan]

Hi Jinjie,

On 12/10/2026 09:23, Jinjie Ruan wrote:
> The current RMID allocator assumes that RMID and CLOSID are entirely
> independent or follow a rigid 2D encoding. This prevents architectures
> where an RMID is bound to a specific CLOSID from properly filtering
> free RMIDs.

Is this patch required for the PARTID narrowing usage in this series? The static mapping is still a
2D encoding.

Thanks,

Ben

> 
> Introduce resctrl_arch_rmid_idx_match() to allow architectures to define
> their own compatibility rules between a target CLOSID and an allocated
> RMID's CLOSID.
> 
> No functional change.



> 
> Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Cc: Dave Martin <Dave.Martin@xxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Babu Moger <babu.moger@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Ben Horgan <ben.horgan@xxxxxxx>
> Cc: Fenghua Yu <fenghuay@xxxxxxxxxx>
> Suggested-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/resctrl.h |  6 ++++++
>  drivers/resctrl/mpam_resctrl.c |  6 ++++++
>  fs/resctrl/monitor.c           | 13 +++----------
>  include/linux/arm_mpam.h       |  1 +
>  4 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 8f6edcdcfd87..7bb297a0ab6e 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -181,6 +181,12 @@ static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid)
>  	return rmid;
>  }
>  
> +/* x86 RMIDs are independent; any RMID can be used with any CLOSID. */
> +static inline bool resctrl_arch_rmid_idx_match(u32 closid, u32 rmid_closid)
> +{
> +	return true;
> +}
> +
>  /* x86 can always read an rmid, nothing needs allocating */
>  struct rdt_resource;
>  static inline void *resctrl_arch_mon_ctx_alloc(struct rdt_resource *r,
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 9d223057953a..385c745787f2 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -279,6 +279,12 @@ u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid)
>  	return closid * (mpam_pmg_max + 1) + rmid;
>  }
>  
> +/* Check if the RMID's associated closid matches the target CLOSID. */
> +bool resctrl_arch_rmid_idx_match(u32 closid, u32 rmid_closid)
> +{
> +	return closid == rmid_closid;
> +}
> +
>  void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
>  {
>  	*closid = idx / (mpam_pmg_max + 1);
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 73413cb128ea..39908f67dea4 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -205,23 +205,16 @@ bool has_busy_rmid(struct rdt_l3_mon_domain *d)
>  static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
>  {
>  	struct rmid_entry *itr;
> -	u32 itr_idx, cmp_idx;
>  
>  	if (list_empty(&rmid_free_lru))
>  		return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-ENOSPC);
>  
>  	list_for_each_entry(itr, &rmid_free_lru, list) {
>  		/*
> -		 * Get the index of this free RMID, and the index it would need
> -		 * to be if it were used with this CLOSID.
> -		 * If the CLOSID is irrelevant on this architecture, the two
> -		 * index values are always the same on every entry and thus the
> -		 * very first entry will be returned.
> +		 * Check if the free RMID matches the target CLOSID.
> +		 * Architecture-specific rules apply.
>  		 */
> -		itr_idx = resctrl_arch_rmid_idx_encode(itr->closid, itr->rmid);
> -		cmp_idx = resctrl_arch_rmid_idx_encode(closid, itr->rmid);
> -
> -		if (itr_idx == cmp_idx)
> +		if (resctrl_arch_rmid_idx_match(closid, itr->closid))
>  			return itr;
>  	}
>  
> diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
> index f92a36187a52..0bc8049a3733 100644
> --- a/include/linux/arm_mpam.h
> +++ b/include/linux/arm_mpam.h
> @@ -60,6 +60,7 @@ void resctrl_arch_sched_in(struct task_struct *tsk);
>  bool resctrl_arch_match_closid(struct task_struct *tsk, u32 closid);
>  bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 closid, u32 rmid);
>  u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid);
> +bool resctrl_arch_rmid_idx_match(u32 closid, u32 rmid_closid);
>  void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid);
>  u32 resctrl_arch_system_num_rmid_idx(void);
>