KVM: s390: pci: Fix memory accounting for pinned/unpinned pages

In the Linux kernel, the following vulnerability has been resolved: KVM: s390: pci: Fix memory accounting for pinned/unpinned pages The account_mem() and unaccount_mem() functions call get_uid() which increments the reference count of struct user_struct on every invocation. But we don't decrement the count by calling free_uid(). It also accounted/unaccounted the pages against the current->mm. But its possible the unaccount_mem() can be called from a different process context than the one that originally pinned the pages. Let's fix this by storing the pinning process user_struct and mm_struct when accounting for pinned pages, and subsequently free these resources when the pages are unpinned. [borntraeger@linux.ibm.com: Fixed whitespace]