Re: [PATCH] arm_mpam: resctrl: Leave CDP off when there are too few PARTIDs

[Jinjie Ruan <ruanjinjie@huawei.com>]

Hi Ben,

Is this modification okay?

在 2026/10/31 10:52, Jinjie Ruan 写道:
> Enabling CDP requires at least 2 PARTIDs. If there are too few PARTIDs,
> resctrl_arch_set_cdp_enabled() returns -EINVAL, but only after it has
> recorded CDP as enabled, halved the monitor count and turned off the
> mbw_max MBA control. resctrl then believes CDP is off, which leaves the
> two sides out of step and the halved monitor count and the missing MBA
> control are not undone.
> 
> Check the PARTID limit before anything is changed so a failed enable has
> no effect.
> 
> Fixes: 6789fb99282c ("arm_mpam: resctrl: Add CDP emulation")
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
> RFC v2 -> v1:
> - Check mpam_partid_max ahead and The partid_d/partid_i determination
>   remains in place.
> - Update the commit message as Ben suggested.
> ---
>  drivers/resctrl/mpam_resctrl.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 5468367776e2..aa3b3a093857 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -210,6 +210,9 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable)
>  	if (enable)
>  		pr_warn("CDP is an expert feature and may cause MPAM to malfunction.\n");
>  
> +	if (enable && mpam_partid_max < 1)
> +		return -EINVAL;
> +
>  	/*
>  	 * resctrl_arch_set_cdp_enabled() is only called with enable set to
>  	 * false on error and unmount.
> @@ -239,9 +242,6 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable)
>  		mpam_resctrl_controls[RDT_RESOURCE_MBA].resctrl_res.alloc_capable = true;
>  
>  	if (enable) {
> -		if (mpam_partid_max < 1)
> -			return -EINVAL;
> -
>  		partid_d = resctrl_get_config_index(RESCTRL_RESERVED_CLOSID, CDP_DATA);
>  		partid_i = resctrl_get_config_index(RESCTRL_RESERVED_CLOSID, CDP_CODE);
>  	}

-- 
Best regards,
Jinjie