/*
* While a process runs, Xen pins its pagetables, which means that the
* hypervisor forces it to be read-only, and it controls all updates
* to it. This means that all pagetable updates have to go via the
* hypervisor, which is moderately expensive.
*
* Since we're pulling the pagetable down, we switch to use init_mm,
* unpin old process pagetable and mark it all read-write, which
* allows further operations on it to be simple memory accesses.
*
* The only subtle point is that another CPU may be still using the
* pagetable because of lazy tlb flushing. This means we need need to
* switch all CPUs off this pagetable before we can unpin it.
*/
void xen_exit_mmap(struct mm_struct *mm)
{
get_cpu(); /* make sure we don't move around */
drop_mm_ref(mm);
put_cpu();
spin_lock(&mm->page_table_lock);
/* pgd may not be pinned in the error exit path of execve */
if (PagePinned(virt_to_page(mm->pgd)))
xen_pgd_unpin(mm->pgd);
spin_unlock(&mm->page_table_lock);
}
static bool xen_page_pinned(void *ptr)
{
struct page *page = virt_to_page(ptr);
return PagePinned(page);
}
