Re: [RFC PATCH v1 1/5] drm/gpusvm: extract drm_gpusvm_hmm_fault() helper

["Huang, Honglei" <honghuan@amd.com>]

On 8/27/2026 3:30 PM, Matthew Brost wrote:
> On Thu, Aug 27, 2026 at 03:14:45PM +0800, Honglei Huang wrote:
>> Make the HMM fault step of drm_gpusvm_get_pages(), including its -EBUSY
>> retry loop, into a helper drm_gpusvm_hmm_fault(). The existing logic of
>> the public drm_gpusvm_get_pages() is not changed, only relocated, so
>> there is no functional change. Keeping the retry loop in common code
>> also means drivers never have to open-code their own fault/retry loop.
>>
>> A single fault can later be shared by several drm_gpusvm_pages instances
>> that mirror the same CPU range. This prepares get_pages() to split the
>> shared MM-level fault from the per-device DMA mapping. No functional
>> change intended.
>>
> 
> I think you might want to just wait on this until Sunday for this
> series. I think this patch [1] is in the core MM tree so when drm-tip
> moves to 7.3.rc1, Sunday, we will have a version of this helper to core
> MM used in gpusvm.

Got it, will wait until Sunday. Thanks for the information.

Regards,
Honglei

> 
> Matt
> 
> [1] https://lore.freedesktop.org/nouveau/20260722-hmm-v10-v1-6-606464dd601a@gmail.com/T/#m68f663ce3e802d7692363c70e6364569134cd6c7
> 
>> Suggested-by: Matthew Brost <matthew.brost@intel.com>
>> Signed-off-by: Honglei Huang <honghuan@amd.com>
>> ---
>>   drivers/gpu/drm/drm_gpusvm.c | 67 ++++++++++++++++++++++++------------
>>   1 file changed, 45 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
>> index fcfe635bc195..507ef6f0a60e 100644
>> --- a/drivers/gpu/drm/drm_gpusvm.c
>> +++ b/drivers/gpu/drm/drm_gpusvm.c
>> @@ -1442,6 +1442,50 @@ static bool drm_gpusvm_pages_valid_unlocked(struct drm_gpusvm *gpusvm,
>>   	return pages_valid;
>>   }
>>   
>> +/**
>> + * drm_gpusvm_hmm_fault() - Run the shared HMM fault for a CPU range
>> + * @gpusvm: Pointer to the GPU SVM structure
>> + * @mm: The mm corresponding to the CPU range
>> + * @hmm_range: The hmm_range to fault.
>> + * @pfns: The pfn array to populate (size @npages)
>> + * @timeout: jiffies deadline for the -EBUSY retry loop
>> + *
>> + * Fault the CPU pages of the range into @pfns. This is the MM level step.
>> + *
>> + * Return: 0 on success, negative error code on failure.
>> + */
>> +static int drm_gpusvm_hmm_fault(struct drm_gpusvm *gpusvm,
>> +				struct mm_struct *mm,
>> +				struct hmm_range *hmm_range,
>> +				unsigned long *pfns,
>> +				unsigned long timeout)
>> +{
>> +	int err;
>> +
>> +	if (!mmget_not_zero(mm))
>> +		return -EFAULT;
>> +
>> +	hmm_range->hmm_pfns = pfns;
>> +	while (true) {
>> +		mmap_read_lock(mm);
>> +		err = hmm_range_fault(hmm_range);
>> +		mmap_read_unlock(mm);
>> +
>> +		if (err == -EBUSY) {
>> +			if (time_after(jiffies, timeout))
>> +				break;
>> +
>> +			hmm_range->notifier_seq =
>> +				mmu_interval_read_begin(hmm_range->notifier);
>> +			continue;
>> +		}
>> +		break;
>> +	}
>> +	mmput(mm);
>> +
>> +	return err;
>> +}
>> +
>>   /**
>>    * drm_gpusvm_get_pages() - Get pages and populate GPU SVM pages struct
>>    * @gpusvm: Pointer to the GPU SVM structure
>> @@ -1503,28 +1547,7 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
>>   	if (!pfns)
>>   		return -ENOMEM;
>>   
>> -	if (!mmget_not_zero(mm)) {
>> -		err = -EFAULT;
>> -		goto err_free;
>> -	}
>> -
>> -	hmm_range.hmm_pfns = pfns;
>> -	while (true) {
>> -		mmap_read_lock(mm);
>> -		err = hmm_range_fault(&hmm_range);
>> -		mmap_read_unlock(mm);
>> -
>> -		if (err == -EBUSY) {
>> -			if (time_after(jiffies, timeout))
>> -				break;
>> -
>> -			hmm_range.notifier_seq =
>> -				mmu_interval_read_begin(notifier);
>> -			continue;
>> -		}
>> -		break;
>> -	}
>> -	mmput(mm);
>> +	err = drm_gpusvm_hmm_fault(gpusvm, mm, &hmm_range, pfns, timeout);
>>   	if (err)
>>   		goto err_free;
>>   
>> -- 
>> 2.34.1
>>