RE: [PATCH v2 07/18] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers

[Yu, Fenghua]

Hi, James,

> When switching tasks, the CLOSID and RMID that the new task should use are
> stored in struct task_struct. For x86 the CLOSID known by resctrl, the value in
> task_struct, and the value written to the CPU register are all the same thing.
> 
> MPAM's CPU interface has two different PARTID's one for data accesses the
> other for instruction fetch. Storing resctrl's CLOSID value in struct task_struct
> implies the arch code knows whether resctrl is using CDP.
> 
> Move the matching and setting of the struct task_struct properties to use
> helpers. This allows arm64 to store the hardware format of the register, instead
> of having to convert it each time.
> 
> __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
> values aren't seen as another CPU may schedule the task being moved while the
> value is being changed. MPAM has an additional corner-case here as the PMG
> bits extend the PARTID space. If the scheduler sees a new-CLOSID but old-RMID,
> the task will dirty an RMID that the limbo code is not watching causing an
> inaccurate count. x86's RMID are independent values, so the limbo code will still
> be watching the old-RMID in this circumstance.
> To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
> Both values must be provided together.
> 
> Because MPAM's RMID values are not unique, the CLOSID must be provided
> when matching the RMID.
> 
> CC: Valentin Schneider <vschneid@xxxxxxxxxx>
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
>  arch/x86/include/asm/resctrl.h         | 18 ++++++++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 57 +++++++++++++++-----------
>  2 files changed, 51 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 44d568f3577c..d589a82995ac 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -95,6 +95,24 @@ static inline unsigned int
> resctrl_arch_round_mon_val(unsigned int val)
>  	return val * scale;
>  }
> 
> +static inline void resctrl_arch_set_closid_rmid(struct task_struct *tsk,
> +						u32 closid, u32 rmid)
> +{
> +	WRITE_ONCE(tsk->closid, closid);
> +	WRITE_ONCE(tsk->rmid, rmid);
> +}
> +
> +static inline bool resctrl_arch_match_closid(struct task_struct *tsk,
> +u32 closid) {
> +	return READ_ONCE(tsk->closid) == closid; }
> +
> +static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
> +					   u32 rmid)
> +{
> +	return READ_ONCE(tsk->rmid) == rmid;
> +}
> +
>  static inline void resctrl_sched_in(void)  {
>  	if (static_branch_likely(&rdt_enable_key))
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e1f879e13823..ced7400decae 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -84,7 +84,7 @@ void rdt_last_cmd_printf(const char *fmt, ...)
>   *
>   * Using a global CLOSID across all resources has some advantages and
>   * some drawbacks:
> - * + We can simply set "current->closid" to assign a task to a resource
> + * + We can simply set current's closid to assign a task to a resource
>   *   group.

Seems this change doesn't gain anything. Maybe this change can be removed?

>   * + Context switch code can avoid extra memory references deciding which
>   *   CLOSID to load into the PQR_ASSOC MSR
> @@ -549,14 +549,26 @@ static void update_task_closid_rmid(struct
> task_struct *t)
>  		_update_task_closid_rmid(t);
>  }
> 
> +static bool task_in_rdtgroup(struct task_struct *tsk, struct rdtgroup
> +*rdtgrp) {
> +	u32 closid, rmid = rdtgrp->mon.rmid;
> +
> +	if (rdtgrp->type == RDTCTRL_GROUP)
> +		closid = rdtgrp->closid;
> +	else if (rdtgrp->type == RDTMON_GROUP)
> +		closid = rdtgrp->mon.parent->closid;
> +	else
> +		return false;
> +
> +	return resctrl_arch_match_closid(tsk, closid) &&
> +	       resctrl_arch_match_rmid(tsk, closid, rmid); }
> +
>  static int __rdtgroup_move_task(struct task_struct *tsk,
>  				struct rdtgroup *rdtgrp)
>  {
>  	/* If the task is already in rdtgrp, no need to move the task. */
> -	if ((rdtgrp->type == RDTCTRL_GROUP && tsk->closid == rdtgrp->closid
> &&
> -	     tsk->rmid == rdtgrp->mon.rmid) ||
> -	    (rdtgrp->type == RDTMON_GROUP && tsk->rmid == rdtgrp-
> >mon.rmid &&
> -	     tsk->closid == rdtgrp->mon.parent->closid))
> +	if (task_in_rdtgroup(tsk, rdtgrp))
>  		return 0;
> 
>  	/*
> @@ -567,19 +579,14 @@ static int __rdtgroup_move_task(struct task_struct
> *tsk,
>  	 * For monitor groups, can move the tasks only from
>  	 * their parent CTRL group.
>  	 */
> -
> -	if (rdtgrp->type == RDTCTRL_GROUP) {
> -		WRITE_ONCE(tsk->closid, rdtgrp->closid);
> -		WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
> -	} else if (rdtgrp->type == RDTMON_GROUP) {
> -		if (rdtgrp->mon.parent->closid == tsk->closid) {
> -			WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
> -		} else {
> -			rdt_last_cmd_puts("Can't move task to different
> control group\n");
> -			return -EINVAL;
> -		}
> +	if (rdtgrp->type == RDTMON_GROUP &&
> +	    !resctrl_arch_match_closid(tsk, rdtgrp->mon.parent->closid)) {
> +		rdt_last_cmd_puts("Can't move task to different control
> group\n");
> +		return -EINVAL;
>  	}
> 
> +	resctrl_arch_set_closid_rmid(tsk, rdtgrp->closid, rdtgrp->mon.rmid);
> +
>  	/*
>  	 * Ensure the task's closid and rmid are written before determining if
>  	 * the task is current that will decide if it will be interrupted.
> @@ -599,14 +606,15 @@ static int __rdtgroup_move_task(struct task_struct
> *tsk,
> 
>  static bool is_closid_match(struct task_struct *t, struct rdtgroup *r)  {
> -	return (rdt_alloc_capable &&
> -	       (r->type == RDTCTRL_GROUP) && (t->closid == r->closid));
> +	return (rdt_alloc_capable && (r->type == RDTCTRL_GROUP) &&
> +		resctrl_arch_match_closid(t, r->closid));
>  }
> 
>  static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r)  {
> -	return (rdt_mon_capable &&
> -	       (r->type == RDTMON_GROUP) && (t->rmid == r->mon.rmid));
> +	return (rdt_mon_capable && (r->type == RDTMON_GROUP) &&
> +		resctrl_arch_match_rmid(t, r->mon.parent->closid,
> +					r->mon.rmid));
>  }
> 
>  /**
> @@ -802,7 +810,7 @@ int proc_resctrl_show(struct seq_file *s, struct
> pid_namespace *ns,
>  		    rdtg->mode != RDT_MODE_EXCLUSIVE)
>  			continue;
> 
> -		if (rdtg->closid != tsk->closid)
> +		if (!resctrl_arch_match_closid(tsk, rdtg->closid))
>  			continue;
> 
>  		seq_printf(s, "res:%s%s\n", (rdtg == &rdtgroup_default) ? "/" : "",
> @@ -810,7 +818,8 @@ int proc_resctrl_show(struct seq_file *s, struct
> pid_namespace *ns,
>  		seq_puts(s, "mon:");
>  		list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
>  				    mon.crdtgrp_list) {
> -			if (tsk->rmid != crg->mon.rmid)
> +			if (!resctrl_arch_match_rmid(tsk, crg->mon.parent-
> >closid,
> +						     crg->mon.rmid))
>  				continue;
>  			seq_printf(s, "%s", crg->kn->name);
>  			break;
> @@ -2401,8 +2410,8 @@ static void rdt_move_group_tasks(struct rdtgroup
> *from, struct rdtgroup *to,
>  	for_each_process_thread(p, t) {
>  		if (!from || is_closid_match(t, from) ||
>  		    is_rmid_match(t, from)) {
> -			WRITE_ONCE(t->closid, to->closid);
> -			WRITE_ONCE(t->rmid, to->mon.rmid);
> +			resctrl_arch_set_closid_rmid(t, to->closid,
> +						     to->mon.rmid);
> 
>  			/*
>  			 * If the task is on a CPU, set the CPU in the mask.
> --
> 2.30.2

Thanks.

-Fenghua