Re: [PATCH v11 0/8] mm/hmm: Add mmap lock-drop support for userfaultfd-backed mappings

[Wei Liu <wei.liu@kernel.org>]

On Thu, Jul 23, 2026 at 02:22:42PM -0700, Andrew Morton wrote:
> On Thu, 23 Jul 2026 10:36:32 -0700 Stanislav Kinsburskii <skinsburskii@gmail.com> wrote:
> 
> > This series extends the HMM framework to support userfaultfd-backed memory
> > by allowing the mmap read lock to be dropped during hmm_range_fault().
> > 
> 
> Thanks, I've updated mm.git to this version.

Hi Andrew,

I see this series in linux-next now.

I'm curious to know if these patches are going to make 7.3.

We have some work that's dependent on this so would like to plan
accordingly.

Thank you Stanislav for continue pushing this.

Thanks,
Wei

> 
> AI review suggests there may be some problems.  Sorry, I don't recall if
> these were considered in previous versions of the patchset:
> 
> 	https://sashiko.dev/#/patchset/20260723-hmm-v10-v11-0-c55b003a4b61@gmail.com
> 
> > 
> > Changes in v11:
> >   - Reject unstable address spaces in hmm_range_fault_unlocked_timeout()
> >     after taking mmap_lock and before walking page tables.
> >   - Compute the remaining HMM timeout budget before the time_after_eq()
> >     check in drm_gpusvm_get_pages() to make sure it can't result in zero
> >     and lead to infinite HMM range faulting loop.
> 
> Here's how v11 altered mm.git:
> 
> 
>  drivers/gpu/drm/drm_gpusvm.c |    4 ++--
>  mm/hmm.c                     |    6 ++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> --- a/drivers/gpu/drm/drm_gpusvm.c~b
> +++ a/drivers/gpu/drm/drm_gpusvm.c
> @@ -1422,11 +1422,11 @@ int drm_gpusvm_get_pages(struct drm_gpus
>  	struct dma_iova_state *state = &svm_pages->state;
>  
>  retry:
> +	remaining = timeout - jiffies;
> +
>  	if (time_after_eq(jiffies, timeout))
>  		return -EBUSY;
>  
> -	remaining = timeout - jiffies;
> -
>  	hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
>  	if (drm_gpusvm_pages_valid_unlocked(gpusvm, svm_pages))
>  		goto set_seqno;
> --- a/mm/hmm.c~b
> +++ a/mm/hmm.c
> @@ -17,6 +17,7 @@
>  #include <linux/slab.h>
>  #include <linux/sched.h>
>  #include <linux/mmzone.h>
> +#include <linux/oom.h>
>  #include <linux/pagemap.h>
>  #include <linux/leafops.h>
>  #include <linux/hugetlb.h>
> @@ -806,6 +807,11 @@ int hmm_range_fault_unlocked_timeout(str
>  		if (ret)
>  			return ret;
>  
> +		if (check_stable_address_space(mm)) {
> +			mmap_read_unlock(mm);
> +			return -EFAULT;
> +		}
> +
>  		if (timeout && time_after(jiffies, deadline)) {
>  			mmap_read_unlock(mm);
>  			return -EBUSY;
> _
>