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

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Aug 27, 2026 at 05:02:43PM +0800, Huang, Honglei wrote:
> 
> 
> 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.
> 

It looks like the core MM helpers have landed in drm-tip [2] but not
gpusvm bits.

If it isn't too much trouble can you pull in version of [3] at the base
of this series, credit Stanislav as the author, and then rebase this
series on top?

We can then merge all of this together into drm-tip.

Matt

[2] 121170831228 mm/hmm: add hmm_range_fault_unlocked_timeout() for mmap lock-drop support
[3] https://lore.freedesktop.org/nouveau/20260722-hmm-v10-v1-6-606464dd601a@gmail.com/T/#m68f663ce3e802d7692363c70e6364569134cd6c7

> 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
> > > 
>