Re: [PATCH v11 05/20] platform/x86/intel/pmt: Do not remap when using callbacks

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] intel_aet: silent telemetry read failure for PMT devices using callbacks
--

commit 43eab3aee86b2e3202e1e7b01c4ce97411570441
Author: Michael J. Ruhl <michael.j.ruhl@intel.com>
Subject: platform/x86/intel/pmt: Do not remap when using callbacks

A callback indicates that the parent driver is responsible for accessing
the data area. Creating a PMT memory remap is redundant. If a read_telem
callback has been provided, do not create a remap.

> diff --git a/drivers/platform/x86/intel/pmt/class.c b/drivers/platform/x86/intel/pmt/class.c
> index 402d51df834a6..1c7a372b4fc42 100644
> --- a/drivers/platform/x86/intel/pmt/class.c
> +++ b/drivers/platform/x86/intel/pmt/class.c
[ ... ]
> @@ -403,14 +403,19 @@ static int intel_pmt_dev_register(struct intel_pmt_entry *entry,
>  	if (!entry->size)
>  		return 0;
>  
> -	res.start = entry->base_addr;
> -	res.end = res.start + entry->size - 1;
> -	res.flags = IORESOURCE_MEM;
> +	/*
> +	 * The read_telem callback is responsible for this mapping, and may have
> +	 * different requirements for use. If the callback is present do not
> +	 * create the map.
> +	 */
> +	if (!(entry->cb && entry->cb->read_telem)) {
> +		struct resource res = DEFINE_RES_MEM(entry->base_addr, entry->size);
>  
> -	entry->base = devm_ioremap_resource(dev, &res);
> -	if (IS_ERR(entry->base)) {
> -		ret = PTR_ERR(entry->base);
> -		goto fail_ioremap;
> +		entry->base = devm_ioremap_resource(dev, &res);
> +		if (IS_ERR(entry->base)) {
> +			ret = PTR_ERR(entry->base);
> +			goto fail_ioremap;
> +		}
>  	}
>  

[Severity: Medium]
When a read_telem callback is provided, entry->base remains NULL.
Could this silently break telemetry reads for Intel AET?

If entry->base is NULL, it propagates to the telemetry endpoint:

drivers/platform/x86/intel/pmt/telemetry.c:pmt_telem_add_endpoint() {
    ...
    ep->base = entry->base;
    ...
}

Then pmt_copy_region() populates the telemetry region with this NULL address:

drivers/platform/x86/intel/pmt/telemetry.c:pmt_copy_region() {
    ...
    region->addr = entry->ep->base;
    ...
}

Finally, in intel_aet_read_event(), the region is skipped because the address is
NULL:

arch/x86/kernel/cpu/resctrl/intel_aet.c:intel_aet_read_event() {
    ...
    for (int i = 0; i < e->pfg->count; i++) {
        if (!e->pfg->regions[i].addr)
            continue;
    ...
}

Because Intel AET strictly requires direct MMIO, it cannot support abstracted
callbacks. This results in a silent failure to collect telemetry data from
AET-monitored devices that use callbacks, since intel_aet_read_event() will
skip the region and return -EINVAL on every read request.

>  	sysfs_bin_attr_init(&entry->pmt_bin_attr);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260923181115.2514193-22-michael.j.ruhl@intel.com?part=5