[RFC PATCH 22/36] arm_mpam: Reset MSC controls from cpu hp callbacks

[James Morse]

Hi Ben,

On 28/07/2025 10:49, Ben Horgan wrote:
> On 7/11/25 19:36, James Morse wrote:
>> When a CPU comes online, it may bring a newly accessible MSC with
>> it. Only the default partid has its value reset by hardware, and
>> even then the MSC might not have been reset since its config was
>> previously dirtyied. e.g. Kexec.
>>
>> Any in-use partid must have its configuration restored, or reset.
>> In-use partids may be held in caches and evicted later.
>>
>> MSC are also reset when CPUs are taken offline to cover cases where
>> firmware doesn't reset the MSC over reboot using UEFI, or kexec
>> where there is no firmware involvement.
>>
>> If the configuration for a RIS has not been touched since it was
>> brought online, it does not need resetting again.
>>
>> To reset, write the maximum values for all discovered controls.
>> diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/
>> mpam_devices.c
>> index 7b042a35405a..d014dbe0ab96 100644
>> --- a/drivers/platform/arm64/mpam/mpam_devices.c
>> +++ b/drivers/platform/arm64/mpam/mpam_devices.c

>> @@ -849,8 +850,116 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>       return 0;
>>   }
>>   +static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
>> +{
>> +    u32 num_words, msb;
>> +    u32 bm = ~0;
>> +    int i;
>> +
>> +    lockdep_assert_held(&msc->part_sel_lock);
>> +
>> +    if (wd == 0)
>> +        return;
>> +
>> +    /*
>> +     * Write all ~0 to all but the last 32bit-word, which may
>> +     * have fewer bits...
>> +     */
>> +    num_words = DIV_ROUND_UP(wd, 32);
>> +    for (i = 0; i < num_words - 1; i++, reg += sizeof(bm))
>> +        __mpam_write_reg(msc, reg, bm);
>> +
>> +    /*
>> +     * ....and then the last (maybe) partial 32bit word. When wd is a
>> +     * multiple of 32, msb should be 31 to write a full 32bit word.
>> +     */
>> +    msb = (wd - 1) % 32;
>> +    bm = GENMASK(msb, 0);
>> +    if (bm)
>> +        __mpam_write_reg(msc, reg, bm);
> Drop the 'if' as the 0 bit will always be part of the mask.

Yup, this was a harmless leftover of the versions that tried to optionally write the left over bits.


>>   @@ -1419,7 +1541,7 @@ static void mpam_enable_once(void)
>>       mpam_register_cpuhp_callbacks(mpam_cpu_online, mpam_cpu_offline);
>>         printk(KERN_INFO "MPAM enabled with %u partid and %u pmg\n",
>> -           mpam_partid_max + 1, mpam_pmg_max + 1);
>> +        READ_ONCE(mpam_partid_max) + 1, mpam_pmg_max + 1);
> 
> Belongs in 'arm_mpam: Probe MSCs to find the supported partid/pmg values'.

That value is now protected by a lock, and can't change at this point, so it no longer needs the READ_ONCE() anyway.


Thanks,

James