On 12/3/2025 11:55 AM, Stanislav Kinsburskii wrote: > On Wed, Dec 03, 2025 at 11:26:23AM -0800, Nuno Das Neves wrote: >> On 12/3/2025 10:24 AM, Stanislav Kinsburskii wrote: >>> Introduce kref-based reference counting and spinlock protection for >>> memory regions in Hyper-V partition management. This change improves >>> memory region lifecycle management and ensures thread-safe access to the >>> region list. >>> >>> Also improves the check for overlapped memory regions during region >>> creation, preventing duplicate or conflicting mappings. >>> >>> Previously, the regions list was protected by the partition mutex. >>> However, this approach is too heavy for frequent fault and invalidation >>> operations. Finer grained locking is now used to improve efficiency and >>> concurrency. >>> >>> This is a precursor to supporting movable memory regions. Fault and >>> invalidation handling for movable regions will require safe traversal of >>> the region list and holding a region reference while performing >>> invalidation or fault operations. >>> >>> Signed-off-by: Stanislav Kinsburskii <[email protected]> >>> --- >>> drivers/hv/mshv_regions.c | 19 ++++++++++++++++--- >>> drivers/hv/mshv_root.h | 6 +++++- >>> drivers/hv/mshv_root_main.c | 32 ++++++++++++++++++++++++-------- >>> 3 files changed, 45 insertions(+), 12 deletions(-) >>> >>> @@ -1657,8 +1670,10 @@ static void destroy_partition(struct mshv_partition >>> *partition) >>> remove_partition(partition); >>> >>> hlist_for_each_entry_safe(region, n, &partition->pt_mem_regions, >>> - hnode) >>> - mshv_region_destroy(region); >>> + hnode) { >>> + hlist_del(®ion->hnode); >>> + mshv_region_put(region); >>> + } >>> >> >> With the following patch introducing movable memory, it looks like the >> list could be traversed by mshv_partition_region_by_gfn() even while >> the this hlist_del() is being called. >> >> Maybe that's not possible for some reason I'm unaware of, could you >> explain why we don't need to spin_lock here for hlist_del()? >> Or, alternatively, use hlist_for_each_entry_safe() in >> mshv_partition_region_by_gfn() to guard against the deletion? >> > > This function (destroy_partition) is called when there are no active > references for neither partition not its VPs (they are destroyed in the > same function above). > In other words, there can't be any callers for mshv_partition_region_by_gfn.
Ah, I see, even if the mmu_notifier is still active, it doesn't traverse the list, as it gets the region by container_of(). Thanks. > > As per mshv_partition_region_by_gfn function itself, the caller is > supposed to take the lock. > > Giving it more thought, I'm strating to think that rw lock her ewould be > a better option than a spinlock + reference count, as regions won't be > added or remove to often and using it would allow to get rid of > reference counting. > > However, this looks like an optimization that isn't required an its > usefulness can be investigated in future. > > Thanks, > Stanislav > >>> /* Withdraw and free all pages we deposited */ >>> hv_call_withdraw_memory(U64_MAX, NUMA_NO_NODE, partition->pt_id); >>> @@ -1856,6 +1871,7 @@ mshv_ioctl_create_partition(void __user *user_arg, >>> struct device *module_dev) >>> >>> INIT_HLIST_HEAD(&partition->pt_devices); >>> >>> + spin_lock_init(&partition->pt_mem_regions_lock); >>> INIT_HLIST_HEAD(&partition->pt_mem_regions); >>> >>> mshv_eventfd_init(partition); >>> >>>
