Re: [PATCH v4 08/10] arm_mpam: add MPAM-Fb MSC firmware access support

Hi Ritwick,

On 7/28/26 12:04, Ritwick Sharma wrote:
> On Thu, Jul 23, 2026 at 05:54:52PM +0200, Andre Przywara wrote:
> 
>> -	WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
>> +	if (msc->iface == MPAM_IFACE_MMIO)
>> +		WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
> 
> I tested the MPAM-Fb series on an Arm AGI CPU.

Many thanks for that, and for reporting on the list!

> I think a similar MPAM_IFACE_MMIO check is needed in
> mpam_msc_zero_mbwu_l(). Without this check, the mapped_hwpage_sz bounds
> check is also performed for an MPAM-Fb MSC, which does not have an MMIO
> mapping. I observed the following warning during testing:
> 
> [   50.638246] WARNING: drivers/resctrl/mpam_devices.c:1266 at mpam_msc_zero_mbwu_l+0x98/0xa8

Ouch, you are right, I missed that one. It seems my very limited testing 
didn't touch that code path.

> There also appears to be an off-by-one issue in the calculation of
> mapped_hwpage_sz:
> 
> 	msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
> 
> The current calculation records a size that is one byte smaller than
> the actual resource. I think this should use resource_size() instead:
> 
> 	msc->mapped_hwpage_sz = resource_size(msc_res);

Well spotted, I can make a separate patch for that, unless you beat me 
to it!

Many thanks,
Andre

> 
> Thanks,
> Ritwick