Re: [PATCH RFC 09/15] arm_mpam: Fix MSC MMIO window size to use resource_size() instead of end - start

[Ben Horgan]

Hi Yin,

On 03/09/2026 11:20, Ben Horgan wrote:
> Hi Yin,
> 
> On 11/08/2026 14:30, Yin Li wrote:
>> struct resource uses an inclusive end address, so the correct size is
>> end - start + 1. The previous calculation of end - start was off by one,
>> resulting in a mapped window one byte smaller than the actual resource.
>> Use resource_size() which correctly computes end - start + 1.
>>
>> Signed-off-by: Yin Li <yin.li@xxxxxxxxxxxxxxxx>
> 
> I just got a kernel ci report for this one which asks for tags:
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202609030809.ObirDhR3-lkp@xxxxxxxxx/
> 
> It doesn't look to give a useful fixes tag though. I'd go with this as that's where the error was
> introduced.
> 
> Fixes: f04046f2577a ("arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate")
> 
> Looks good to me.
> 
> Reviewed-by: Ben Horgan <ben.horgan@xxxxxxx>

Scratch that. As Ilpo points out,[1], there is no functional bug but just some misleading naming
which never the less would be good to fix. This does require > in the warnings becoming >= though
and there would be no need for fixes tag. Do you agree with this analysis?

Thanks,

Ben

[1]
https://lore.kernel.org/lkml/03055fbc-281f-4ed9-9282-4853d560e17f@xxxxxxx/T/#mdb57d40c888ff4ce656a9d9a00ecf5d99466530c


> 
> Thanks,
> 
> Ben
> 
>> ---
>>  drivers/resctrl/mpam_devices.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 1e082fb60e30..5d1854d97371 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -2296,7 +2296,7 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
>>  			dev_err_once(dev, "Failed to map MSC base address\n");
>>  			return ERR_CAST(io);
>>  		}
>> -		msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
>> +		msc->mapped_hwpage_sz = resource_size(msc_res);
>>  		msc->mapped_hwpage = io;
>>  	} else {
>>  		return ERR_PTR(-EINVAL);
>>
>