Sean Christopherson <[email protected]> writes: > On Tue, Jul 28, 2026, Tarun Sahu wrote: >> +/** >> + * kvm_gmem_freeze - Freeze or unfreeze a guest_memfd inode mapping. >> + * @inode: The guest_memfd inode. >> + * @freeze: True to freeze, false to unfreeze. >> + * >> + * This API is used strictly during the live update / preservation >> transition >> + * window to prevent host userspace and guest-side faults from making any >> + * mapping modifications (such as fallocate or page fault allocation) >> + * to the guest_memfd page cache. >> + * >> + * Synchronization Strategy (Sleepable RCU): >> + * To avoid high-contention VFS locks (like inode_lock or >> + * filemap_invalidate_lock) on the vCPU page fault hot paths, this subsystem >> + * implements a lightweight, system-wide Sleepable RCU (SRCU) mechanism >> + * (`kvm_gmem_freeze_srcu`): >> + * >> + * Global vs. Per-Inode SRCU >> + * ====================== >> + * A single system-wide global static `srcu_struct` is used instead of a >> + * per-inode SRCU structure to completely prevent unprivileged users from >> + * exhausting the host's per-CPU memory allocator. > > This argument doesn't hold up given that each kvm structure has two SRCU > structs.
Ohh okay. I was very skeptic that per-cpu structure are not counted in cgroups and liveupdate is once in a while usecase So avoided making it per-cpu. But otherwise I am fine with going with per-cpu. Will take care of it in next revision. Thanks ~Tarun
