arm64/mpam: Fix MBWU monitor overflow handling

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

Posted by Zeng Heng 3 months, 2 weeks ago

Bandwidth counters need to run continuously to correctly reflect the
bandwidth. When reading the previously configured MSMON_CFG_MBWU_CTL,
software must recognize that the MSMON_CFG_x_CTL_OFLOW_STATUS bit may
have been set by hardware because of the counter overflow.

The existing logic incorrectly treats this bit as an indication that the
monitor configuration has been changed and consequently zeros the MBWU
statistics by mistake.

Also fix the handling of overflow amount calculation. There's no need to
subtract mbwu_state->prev_val when calculating overflow_val.

Signed-off-by: Zeng Heng <zengheng4@huawei.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);
 
 	if (config_mismatch || reset_on_next_read)
 		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
@@ -1138,8 +1139,9 @@ static void __ris_msmon_read(void *arg)
 		mbwu_state = &ris->mbwu_state[ctx->mon];
 
 		/* Add any pre-overflow value to the mbwu_state->val */
-		if (mbwu_state->prev_val > now)
-			overflow_val = mpam_msmon_overflow_val(m->type) - mbwu_state->prev_val;
+		if (mbwu_state->prev_val > now &&
+		   (cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS))
+			overflow_val = mpam_msmon_overflow_val(ris);
 
 		mbwu_state->prev_val = now;
 		mbwu_state->correction += overflow_val;
-- 
2.25.1

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

Posted by Ben Horgan 3 months, 2 weeks ago

Hi Zeng,

On 10/22/25 14:39, Zeng Heng wrote:
> Bandwidth counters need to run continuously to correctly reflect the
> bandwidth. When reading the previously configured MSMON_CFG_MBWU_CTL,
> software must recognize that the MSMON_CFG_x_CTL_OFLOW_STATUS bit may
> have been set by hardware because of the counter overflow.
> 
> The existing logic incorrectly treats this bit as an indication that the
> monitor configuration has been changed and consequently zeros the MBWU
> statistics by mistake.

By zero-ing when the overflow bit is set we miss out on the counts after
the overflow and before the zero-ing. Do I understand correctly, that
this what this patch is aiming to fix?

> 
> Also fix the handling of overflow amount calculation. There's no need to
> subtract mbwu_state->prev_val when calculating overflow_val.

Why not? Isn't this the pre-overflow part that we are missing from the
running count?

> 
> Signed-off-by: Zeng Heng <zengheng4@huawei.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. Also, as the overflow bit is no longer
reset due to the config mismatch it needs to be reset somewhere else.

>  
>  	if (config_mismatch || reset_on_next_read)
>  		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> @@ -1138,8 +1139,9 @@ static void __ris_msmon_read(void *arg)
>  		mbwu_state = &ris->mbwu_state[ctx->mon];
>  
>  		/* Add any pre-overflow value to the mbwu_state->val */
> -		if (mbwu_state->prev_val > now)
> -			overflow_val = mpam_msmon_overflow_val(m->type) - mbwu_state->prev_val;
> +		if (mbwu_state->prev_val > now &&
> +		   (cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS))
> +			overflow_val = mpam_msmon_overflow_val(ris);
>  
>  		mbwu_state->prev_val = now;
>  		mbwu_state->correction += overflow_val;


Thanks,

Ben

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

Posted by Zeng Heng 3 months, 2 weeks ago

Hi Ben,

On 2025/10/23 0:17, Ben Horgan wrote:

>> Signed-off-by: Zeng Heng <zengheng4@huawei.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?

Best Regards,
Zeng Heng

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

Posted by Ben Horgan 3 months, 1 week ago

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@huawei.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.

> 
> Best Regards,
> Zeng Heng
> 
> 

Thanks,

Ben

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

Posted by Zeng Heng 3 months, 1 week ago

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@huawei.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

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

Posted by Zeng Heng 3 months, 1 week ago

Hi Ben,

On 2025/10/29 10:49, Zeng Heng wrote:
> 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@huawei.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.
> 

Please disregard my previous mail... :)

Exactly, thanks for the review. I'll fold the fixes into v2 of the
patch.


Best Regards,
Zeng Heng

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

Posted by Zeng Heng 3 months, 2 weeks ago

Hi Ben,

On 2025/10/23 0:17, Ben Horgan wrote:
>>
>> Also fix the handling of overflow amount calculation. There's no need to
>> subtract mbwu_state->prev_val when calculating overflow_val.
> 
> Why not? Isn't this the pre-overflow part that we are missing from the
> running count?
> 

The MSMON_MBWU register accumulates counts monotonically forward and
would not automatically cleared to zero on overflow.

The overflow portion is exactly what mpam_msmon_overflow_val() computes,
there is no need to additionally subtract mbwu_state->prev_val.

>>
>> Signed-off-by: Zeng Heng <zengheng4@huawei.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. Also, as the overflow bit is no longer
> reset due to the config mismatch it needs to be reset somewhere else.

Yes, overflow bit needs to be cleared somewhere. I try to point out in
the next patch mail.

Best Regards,
Zeng Heng

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

Posted by Ben Horgan 3 months, 1 week ago

Hi Zeng,

On 10/25/25 09:45, Zeng Heng wrote:
> Hi Ben,
> 
> On 2025/10/23 0:17, Ben Horgan wrote:
>>>
>>> Also fix the handling of overflow amount calculation. There's no need to
>>> subtract mbwu_state->prev_val when calculating overflow_val.
>>
>> Why not? Isn't this the pre-overflow part that we are missing from the
>> running count?
>>
> 
> The MSMON_MBWU register accumulates counts monotonically forward and
> would not automatically cleared to zero on overflow.
> 
> The overflow portion is exactly what mpam_msmon_overflow_val() computes,
> there is no need to additionally subtract mbwu_state->prev_val.

Yes, I now see you are correct. The 'correction' ends up holding
(counter size) * (number of overflows) and the current value of the
counter plus this gives you the bandwidth use up until now.

> 
>>>
>>> Signed-off-by: Zeng Heng <zengheng4@huawei.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. Also, as the overflow bit is no longer
>> reset due to the config mismatch it needs to be reset somewhere else.
> 
> Yes, overflow bit needs to be cleared somewhere. I try to point out in
> the next patch mail.

I had misunderstood before but the current code in the series doesn't
make use of overflow bit and just relies on prev_val > now. Using
overflow status does give us a bit more lee-way for overflowing so is a
useful enhancement.

> 
> Best Regards,
> Zeng Heng
> 
> 
Thanks,

Ben

[PATCH] arm64/mpam: Clean MBWU monitor overflow bit

Posted by Zeng Heng 3 months, 2 weeks ago

The MSMON_MBWU register accumulates counts monotonically forward and
would not automatically cleared to zero on overflow. The overflow portion
is exactly what mpam_msmon_overflow_val() computes, there is no need to
additionally subtract mbwu_state->prev_val.

Before invoking write_msmon_ctl_flt_vals(), the overflow bit of the
MSMON_MBWU register must first be read to prevent it from being
inadvertently cleared by the write operation. Then, before updating the
monitor configuration, the overflow bit should be cleared to zero.

Finally, use the overflow bit instead of relying on counter wrap-around
to determine whether an overflow has occurred, that avoids the case where
a wrap-around (now > prev_val) is overlooked.

Signed-off-by: Zeng Heng <zengheng4@huawei.com>
---
 drivers/resctrl/mpam_devices.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 0dd048279e02..575980e3a366 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1062,6 +1062,21 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
 	}
 }
 
+static bool read_msmon_mbwu_is_overflow(struct mpam_msc *msc)
+{
+	u32 ctl;
+	bool overflow;
+
+	ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
+	overflow = ctl & MSMON_CFG_x_CTL_OFLOW_STATUS ? true : false;
+
+	if (overflow)
+		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl &
+				     ~MSMON_CFG_x_CTL_OFLOW_STATUS);
+
+	return overflow;
+}
+
 /* Call with MSC lock held */
 static void __ris_msmon_read(void *arg)
 {
@@ -1069,6 +1084,7 @@ static void __ris_msmon_read(void *arg)
 	bool config_mismatch;
 	struct mon_read *m = arg;
 	u64 now, overflow_val = 0;
+	bool mbwu_overflow = false;
 	struct mon_cfg *ctx = m->ctx;
 	bool reset_on_next_read = false;
 	struct mpam_msc_ris *ris = m->ris;
@@ -1091,6 +1107,7 @@ static void __ris_msmon_read(void *arg)
 			reset_on_next_read = mbwu_state->reset_on_next_read;
 			mbwu_state->reset_on_next_read = false;
 		}
+		mbwu_overflow = read_msmon_mbwu_is_overflow(msc);
 	}
 
 	/*
@@ -1138,8 +1155,8 @@ static void __ris_msmon_read(void *arg)
 		mbwu_state = &ris->mbwu_state[ctx->mon];
 
 		/* Add any pre-overflow value to the mbwu_state->val */
-		if (mbwu_state->prev_val > now)
-			overflow_val = mpam_msmon_overflow_val(m->type) - mbwu_state->prev_val;
+		if (mbwu_overflow)
+			overflow_val = mpam_msmon_overflow_val(m->type);
 
 		mbwu_state->prev_val = now;
 		mbwu_state->correction += overflow_val;
-- 
2.25.1

Re: [PATCH] arm64/mpam: Clean MBWU monitor overflow bit

Posted by Ben Horgan 3 months, 1 week ago

Hi Zeng,

On 10/25/25 10:34, Zeng Heng wrote:
> The MSMON_MBWU register accumulates counts monotonically forward and
> would not automatically cleared to zero on overflow. The overflow portion
> is exactly what mpam_msmon_overflow_val() computes, there is no need to
> additionally subtract mbwu_state->prev_val.
> 
> Before invoking write_msmon_ctl_flt_vals(), the overflow bit of the
> MSMON_MBWU register must first be read to prevent it from being
> inadvertently cleared by the write operation. Then, before updating the
> monitor configuration, the overflow bit should be cleared to zero.
> 
> Finally, use the overflow bit instead of relying on counter wrap-around
> to determine whether an overflow has occurred, that avoids the case where
> a wrap-around (now > prev_val) is overlooked.
> 
> Signed-off-by: Zeng Heng <zengheng4@huawei.com>
> ---
>  drivers/resctrl/mpam_devices.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 0dd048279e02..575980e3a366 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1062,6 +1062,21 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
>  	}
>  }
>  
> +static bool read_msmon_mbwu_is_overflow(struct mpam_msc *msc)
> +{
> +	u32 ctl;
> +	bool overflow;
> +
> +	ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
> +	overflow = ctl & MSMON_CFG_x_CTL_OFLOW_STATUS ? true : false;
> +
> +	if (overflow)
> +		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl &
> +				     ~MSMON_CFG_x_CTL_OFLOW_STATUS);


Seems sensible. It's best to consider the overflow status bit for long
counters as well. Although, that's introduced later in the series so
depends on patch ordering. (Sorry, was considering patches on top of the
full series when I commented on counter length before.)

> +
> +	return overflow;
> +}
> +
>  /* Call with MSC lock held */
>  static void __ris_msmon_read(void *arg)
>  {
> @@ -1069,6 +1084,7 @@ static void __ris_msmon_read(void *arg)
>  	bool config_mismatch;
>  	struct mon_read *m = arg;
>  	u64 now, overflow_val = 0;
> +	bool mbwu_overflow = false;
>  	struct mon_cfg *ctx = m->ctx;
>  	bool reset_on_next_read = false;
>  	struct mpam_msc_ris *ris = m->ris;
> @@ -1091,6 +1107,7 @@ static void __ris_msmon_read(void *arg)
>  			reset_on_next_read = mbwu_state->reset_on_next_read;
>  			mbwu_state->reset_on_next_read = false;
>  		}
> +		mbwu_overflow = read_msmon_mbwu_is_overflow(msc);

If the config is then found to mismatch, then mbwu_overflow can be
subsequently set to false.

>  	}
>  
>  	/*
> @@ -1138,8 +1155,8 @@ static void __ris_msmon_read(void *arg)
>  		mbwu_state = &ris->mbwu_state[ctx->mon];
>  
>  		/* Add any pre-overflow value to the mbwu_state->val */
> -		if (mbwu_state->prev_val > now)
> -			overflow_val = mpam_msmon_overflow_val(m->type) - mbwu_state->prev_val;
> +		if (mbwu_overflow)
> +			overflow_val = mpam_msmon_overflow_val(m->type);

Yep, makes sense.

>  
>  		mbwu_state->prev_val = now;

With this prev_val no longer has any use.

>  		mbwu_state->correction += overflow_val;
Thanks,

Ben