linux-kernel - Re: [PATCH mpam mpam/snapshot/v6.14-rc1] arm64/mpam: Fix MBWU monitor overflow handling

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Message-ID: <d2aa99f8-dbdc-dc13-1ba3-0e273913221f@huawei.com>
Date: Wed, 29 Oct 2025 10:49:10 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: Ben Horgan <ben.horgan@....com>, <james.morse@....com>
CC: <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
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Subject: Re: [PATCH mpam mpam/snapshot/v6.14-rc1] arm64/mpam: Fix MBWU monitor
 overflow handling

Hi Ben,

On 2025/10/29 0:01, Ben Horgan wrote:
> Hi Zeng,
> 
> On 10/25/25 10:01, Zeng Heng wrote:
>> Hi Ben,
>>
>> On 2025/10/23 0:17, Ben Horgan wrote:
>>
>>>> Signed-off-by: Zeng Heng <zengheng4@...wei.com>
>>>> ---
>>>>    drivers/resctrl/mpam_devices.c | 8 +++++---
>>>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/
>>>> mpam_devices.c
>>>> index 0dd048279e02..06f3ec9887d2 100644
>>>> --- a/drivers/resctrl/mpam_devices.c
>>>> +++ b/drivers/resctrl/mpam_devices.c
>>>> @@ -1101,7 +1101,8 @@ static void __ris_msmon_read(void *arg)
>>>>        clean_msmon_ctl_val(&cur_ctl);
>>>>        gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
>>>>        config_mismatch = cur_flt != flt_val ||
>>>> -              cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
>>>> +             (cur_ctl & ~MSMON_CFG_x_CTL_OFLOW_STATUS) !=
>>>> +             (ctl_val | MSMON_CFG_x_CTL_EN);
>>>
>>> This only considers 31 bit counters. I would expect any change here to
>>> consider all lengths of counter.
>>
>> Sorry, regardless of whether the counter is 32-bit or 64-bit, the
>> config_mismatch logic should be handled the same way here. Am I
>> wrong?
> 
> Yes, they should be handled the same way. However, the overflow status
> bit for long counters is MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L.
> 
> I now see that the existing code in the series has this covered.
> Both the overflow bits are masked out in clean_msmon_ctl_val(). No need
> for any additional masking.
> 

Yes, I’ve seen the usage, except that clearing the overflow bit in the
register is missing.


Best Regards,
Zeng Heng