Re: [PATCH 5.15.y] powercap: intel_rapl: Do not change CLAMPING bit if ENABLE bit cannot be changed

[Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>]

Hi Sasha,


Question inline from a backport point of view:
On 21/07/25 05:45, Sasha Levin wrote:
> From: Zhang Rui <rui.zhang@intel.com>
> 
> [ Upstream commit 964209202ebe1569c858337441e87ef0f9d71416 ]
> 
> PL1 cannot be disabled on some platforms. The ENABLE bit is still set
> after software clears it. This behavior leads to a scenario where, upon
> user request to disable the Power Limit through the powercap sysfs, the
> ENABLE bit remains set while the CLAMPING bit is inadvertently cleared.
> 
> According to the Intel Software Developer's Manual, the CLAMPING bit,
> "When set, allows the processor to go below the OS requested P states in
> order to maintain the power below specified Platform Power Limit value."
> 
> Thus this means the system may operate at higher power levels than
> intended on such platforms.
> 
> Enhance the code to check ENABLE bit after writing to it, and stop
> further processing if ENABLE bit cannot be changed.
> 
> Reported-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> Fixes: 2d281d8196e3 ("PowerCap: Introduce Intel RAPL power capping driver")
> Cc: All applicable <stable@vger.kernel.org>
> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> Link: https://patch.msgid.link/20250619071340.384782-1-rui.zhang@intel.com
> [ rjw: Use str_enabled_disabled() instead of open-coded equivalent ]
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> [ replaced rapl_write_pl_data() and rapl_read_pl_data() with rapl_write_data_raw() and rapl_read_data_raw() ]
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>   drivers/powercap/intel_rapl_common.c | 23 ++++++++++++++++++++++-
>   1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c
> index 9dfc053878fda..40d149d9dce85 100644
> --- a/drivers/powercap/intel_rapl_common.c
> +++ b/drivers/powercap/intel_rapl_common.c
> @@ -212,12 +212,33 @@ static int find_nr_power_limit(struct rapl_domain *rd)
>   static int set_domain_enable(struct powercap_zone *power_zone, bool mode)
>   {
>   	struct rapl_domain *rd = power_zone_to_rapl_domain(power_zone);
> +	u64 val;
> +	int ret;
>   
>   	if (rd->state & DOMAIN_STATE_BIOS_LOCKED)
>   		return -EACCES;
>   
>   	cpus_read_lock();
> -	rapl_write_data_raw(rd, PL1_ENABLE, mode);
> +	ret = rapl_write_data_raw(rd, PL1_ENABLE, mode);
> +	if (ret) {
> +		cpus_read_unlock();
> +		return ret;
> +	}
> +
> +	/* Check if the ENABLE bit was actually changed */
> +	ret = rapl_read_data_raw(rd, PL1_ENABLE, true, &val);
> +	if (ret) {
> +		cpus_read_unlock();
> +		return ret;
> +	}

Shouldn't this be rapl_read_data_raw(rd, PL1_ENABLE, false, &val); ?


Thanks
Harshit
> +
> +	if (mode != val) {
> +		pr_debug("%s cannot be %s\n", power_zone->name,
> +			 mode ? "enabled" : "disabled");
> +		cpus_read_unlock();
> +		return 0;
> +	}
> +
>   	if (rapl_defaults->set_floor_freq)
>   		rapl_defaults->set_floor_freq(rd, mode);
>   	cpus_read_unlock();