Re: [PATCH v7 4/8] mshv: Use hmm_range_fault_unlocked_timeout() for region faults

[Jason Gunthorpe]

On Tue, Jul 07, 2026 at 12:47:15PM -0700, Stanislav Kinsburskii wrote:
> MSHV currently faults movable memory regions by taking mmap_read_lock()
> around hmm_range_fault(). That prevents the fault path from handling VMAs
> whose fault handlers need to drop mmap_lock, such as userfaultfd-backed
> mappings.
> 
> Use hmm_range_fault_unlocked_timeout() instead. Passing a timeout of 0
> preserves MSHV's existing unbounded retry behavior while letting the HMM
> helper own mmap_lock acquisition and refresh range->notifier_seq internally
> before walking the range. After the fault succeeds, MSHV still takes
> mreg_mutex and checks mmu_interval_read_retry() before installing the pages
> into the region, so the existing invalidation synchronization is preserved.
> 
> Fold the small fault-and-lock helper into mshv_region_range_fault(), since
> the remaining retry path is just the standard "fault, take the driver lock,
> check the interval notifier sequence" pattern.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxx>
> ---
>  drivers/hv/mshv_regions.c |   54 ++++++++-------------------------------------
>  1 file changed, 10 insertions(+), 44 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason