Re: [PATCH v8 8/8] drm/gpusvm: Use hmm_range_fault_unlocked_timeout() for range faults

[Stanislav Kinsburskii <skinsburskii@gmail.com>]

On Mon, Jul 13, 2026 at 09:30:35AM -0700, Matthew Brost wrote:
> On Fri, Jul 10, 2026 at 02:27:19PM -0700, Stanislav Kinsburskii wrote:
> 
> Please send series like this to intel-xe@lists.freedesktop.org list too
> as this will trigger our CI which expercises the change paths changed in
> this series.
> 
> > Several GPU SVM paths take mmap_read_lock() only to call hmm_range_fault(),
> > then retry -EBUSY until HMM_RANGE_DEFAULT_TIMEOUT expires. Those paths use
> > MMU interval notifiers whose mm matches the mm that was locked for the HMM
> > fault.
> > 
> > Use hmm_range_fault_unlocked_timeout() for those faults and pass the
> > remaining retry budget to HMM. The helper owns mmap_lock acquisition and
> > refreshes range->notifier_seq internally for each retry, while GPU SVM
> > keeps its existing driver-lock validation with mmu_interval_read_retry()
> > after a successful fault.
> > 
> > Leave drm_gpusvm_check_pages() on hmm_range_fault() because that path is
> > called with the mmap lock already held by its caller.
> > 
> > Signed-off-by: Stanislav Kinsburskii <skinsburskii@gmail.com>
> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> > ---
> >  drivers/gpu/drm/drm_gpusvm.c |   52 ++++++------------------------------------
> >  1 file changed, 7 insertions(+), 45 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> > index 958cb605aedd..6b7a6eaebcd9 100644
> > --- a/drivers/gpu/drm/drm_gpusvm.c
> > +++ b/drivers/gpu/drm/drm_gpusvm.c
> > @@ -788,22 +788,8 @@ enum drm_gpusvm_scan_result drm_gpusvm_scan_mm(struct drm_gpusvm_range *range,
> >  	hmm_range.hmm_pfns = pfns;
> >  
> >  retry:
> > -	hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
> > -	mmap_read_lock(range->gpusvm->mm);
> > -
> > -	while (true) {
> > -		err = hmm_range_fault(&hmm_range);
> > -		if (err == -EBUSY) {
> > -			if (time_after(jiffies, timeout))
> > -				break;
> > -
> > -			hmm_range.notifier_seq =
> > -				mmu_interval_read_begin(notifier);
> > -			continue;
> > -		}
> > -		break;
> > -	}
> > -	mmap_read_unlock(range->gpusvm->mm);
> > +	err = hmm_range_fault_unlocked_timeout(&hmm_range,
> > +					       max(timeout - jiffies, 1L));
> >  	if (err)
> >  		goto err_free;
> >  
> > @@ -1439,21 +1425,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
> >  	}
> >  
> >  	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;
> > -	}
> > +	err = hmm_range_fault_unlocked_timeout(&hmm_range,
> > +				max_t(long, timeout - jiffies, 1));
> 
> Unaligned indentation.
> 
> So I'd write this like this to avoid weird wraps:
> 
> ctimeout = max_t(long, timeout - jiffies, 1));
> err = hmm_range_fault_unlocked_timeout(&hmm_range, ctimeout);
> 
> >  	mmput(mm);
> >  	if (err)
> >  		goto err_free;
> > @@ -1736,24 +1709,13 @@ int drm_gpusvm_range_evict(struct drm_gpusvm *gpusvm,
> >  		return -ENOMEM;
> >  
> >  	hmm_range.hmm_pfns = pfns;
> > -	while (!time_after(jiffies, timeout)) {
> > -		hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
> > -		if (time_after(jiffies, timeout)) {
> > -			err = -ETIME;
> > -			break;
> > -		}
> > -
> > -		mmap_read_lock(mm);
> > -		err = hmm_range_fault(&hmm_range);
> > -		mmap_read_unlock(mm);
> > -		if (err != -EBUSY)
> > -			break;
> > -	}
> > +	err = hmm_range_fault_unlocked_timeout(&hmm_range,
> > +				max_t(long, timeout - jiffies, 1));
> >  
> 
> Same here.
> 
> Nits, aside LGTM.
> 

Will change as requested and send to intel-xe@lists.freedesktop.org next time.

Thanks,
Stanislav

> Matt
> 
> >  	kvfree(pfns);
> >  	mmput(mm);
> >  
> > -	return err;
> > +	return err == -EBUSY ? -ETIME : err;
> >  }
> >  EXPORT_SYMBOL_GPL(drm_gpusvm_range_evict);
> >  
> > 
> >