Re: [PATCH 07/23] perf/x86: Apply PMU partition mask on static constraints

[Mi, Dapeng]

It seems not a good practice for me to modify all the places calling these
static constraints. We could have to add new get_event_constraints()
helpers for future platforms, and we have to duplicate these
part_constraint() code.

Could we leverage the dynamic constraint mechanism?  We can set the
event->hw.dyn_constraint to be host counters mask, then we don't need any
specific change for these static constraints.

Thanks.

On 8/22/2026 6:19 AM, Zide Chen wrote:
> Static, counter-specific constraints used for attr.precise_ip == 3, or
> other special cases bypass intel_get_event_constraints(), which is
> where partition_mask is applied via dyn_constraint().
>
> As a result, such a host !exclude_guest event can still be scheduled
> onto a counter that partition_mask reserves for the guest, causing
> host and guest to share the same hardware counter.
>
> Some of these static constraint paths, e.g. glp or cmt, are currently
> only reachable on platforms that don't support PerfMon masking. Still,
> apply part_constraint() to all of them uniformly, so future platforms
> that combine PerfMon masking with these constraint paths are not
> silently exposed to this bug.
>
> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
> ---
>  arch/x86/events/intel/core.c | 39 +++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 7951accfcf2c..0f76e56fd2db 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -4459,6 +4459,9 @@ dyn_constraint(struct cpu_hw_events *cpuc, struct event_constraint *c, int idx)
>   * Mask out guest-owned counters from a constraint when PMU partition has been
>   * entered, so !exclude_guest host events are not scheduled onto them while
>   * the CPU is in non-root mode.
> + *
> + * This is also used by PMU-specific get_event_constraints() wrappers
> + * that hard-code a static, counter-specific constraint.
>   */
>  static struct event_constraint *
>  part_constraint(struct cpu_hw_events *cpuc, int idx,
> @@ -5568,7 +5571,7 @@ hsw_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  	/* Handle special quirk on in_tx_checkpointed only in counter 2 */
>  	if (event->hw.config & HSW_IN_TX_CHECKPOINTED) {
>  		if (c->idxmsk64 & (1U << 2))
> -			return &counter2_constraint;
> +			return part_constraint(cpuc, idx, event, &counter2_constraint);
>  		return &emptyconstraint;
>  	}
>  
> @@ -5585,7 +5588,7 @@ icl_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  	 */
>  	if ((event->attr.precise_ip == 3) &&
>  	    constraint_match(&fixed0_constraint, event->hw.config))
> -		return &fixed0_constraint;
> +		return part_constraint(cpuc, idx, event, &fixed0_constraint);
>  
>  	return hsw_get_event_constraints(cpuc, idx, event);
>  }
> @@ -5607,7 +5610,7 @@ glc_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  	if ((event->attr.precise_ip == 3) &&
>  	    !constraint_match(&fixed0_constraint, event->hw.config)) {
>  		if (c->idxmsk64 & BIT_ULL(0))
> -			return &counter0_constraint;
> +			return part_constraint(cpuc, idx, event, &counter0_constraint);
>  
>  		return &emptyconstraint;
>  	}
> @@ -5623,7 +5626,7 @@ glp_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  
>  	/* :ppp means to do reduced skid PEBS which is PMC0 only. */
>  	if (event->attr.precise_ip == 3)
> -		return &counter0_constraint;
> +		return part_constraint(cpuc, idx, event, &counter0_constraint);
>  
>  	c = intel_get_event_constraints(cpuc, idx, event);
>  
> @@ -5645,9 +5648,9 @@ tnt_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  	if (event->attr.precise_ip == 3) {
>  		/* Force instruction:ppp on PMC0 and Fixed counter 0 */
>  		if (constraint_match(&fixed0_constraint, event->hw.config))
> -			return &fixed0_counter0_constraint;
> +			return part_constraint(cpuc, idx, event, &fixed0_counter0_constraint);
>  
> -		return &counter0_constraint;
> +		return part_constraint(cpuc, idx, event, &counter0_constraint);
>  	}
>  
>  	return c;
> @@ -5705,22 +5708,30 @@ cmt_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  	if (event->attr.precise_ip == 3) {
>  		/* Force instruction:ppp on PMC0, 1 and Fixed counter 0 */
>  		if (constraint_match(&fixed0_constraint, event->hw.config)) {
> +			c = &fixed0_counter0_1_constraint;
> +
>  			/* The fixed counter 0 doesn't support LBR event logging. */
>  			if (branch_sample_counters(event))
> -				return &counter0_1_constraint;
> -			else
> -				return &fixed0_counter0_1_constraint;
> +				c = &counter0_1_constraint;
> +
> +			return part_constraint(cpuc, idx, event, c);
>  		}
>  
>  		switch (c->idxmsk64 & 0x3ull) {
>  		case 0x1:
> -			return &counter0_constraint;
> +			c = &counter0_constraint;
> +			break;
>  		case 0x2:
> -			return &counter1_constraint;
> +			c = &counter1_constraint;
> +			break;
>  		case 0x3:
> -			return &counter0_1_constraint;
> +			c = &counter0_1_constraint;
> +			break;
> +		default:
> +			c = &emptyconstraint;
> +			break;
>  		}
> -		return &emptyconstraint;
> +		return part_constraint(cpuc, idx, event, c);
>  	}
>  
>  	return c;
> @@ -5744,7 +5755,7 @@ rwc_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>  		 */
>  		if (event->attr.precise_ip == 3)
>  			return &emptyconstraint;
> -		return &counters_1_7_constraint;
> +		return part_constraint(cpuc, idx, event, &counters_1_7_constraint);
>  	}
>  
>  	return c;