KVM: Set file_operations.owner appropriately for all such structures

KVM: Set file_operations.owner appropriately for all such structures

Set .owner for all KVM-owned filed types so that the KVM module is pinned
until any files with callbacks back into KVM are completely freed.  Using
"struct kvm" as a proxy for the module, i.e. keeping KVM-the-module alive
while there are active VMs, doesn't provide full protection.

Userspace can invoke delete_module() the instant the last reference to KVM
is put.  If KVM itself puts the last reference, e.g. via kvm_destroy_vm(),
then it's possible for KVM to be preempted and deleted/unloaded before KVM
fully exits, e.g. when the task running kvm_destroy_vm() is scheduled back
in, it will jump to a code page that is no longer mapped.

Note, file types that can call into sub-module code, e.g. kvm-intel.ko or
kvm-amd.ko on x86, must use the module pointer passed to kvm_init(), not
THIS_MODULE (which points at kvm.ko).  KVM assumes that if /dev/kvm is
reachable, e.g. VMs are active, then the vendor module is loaded.

To reduce the probability of forgetting to set .owner entirely, use
THIS_MODULE for stats files where KVM does not call back into vendor code.

This reverts commit 70375c2d8fa3fb9b0b59207a9c5df1e2e1205c10, and fixes
several other file types that have been buggy since their introduction.

Fixes: 70375c2d8fa3 ("Revert "KVM: set owner of cpu and vm file operations"")
Fixes: 3bcd0662d66f ("KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/all/20231010003746.GN800259@ZenIV
Link: https://lore.kernel.org/r/20231018204624.1905300-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>