+/*
+ * If PTI is enabled, this maps the LDT into the kernelmode and
+ * usermode tables for the given mm.
+ *
+ * There is no corresponding unmap function. Even if the LDT is freed, we
+ * leave the PTEs around until the slot is reused or the mm is destroyed.
+ * This is harmless: the LDT is always in ordinary memory, and no one will
+ * access the freed slot.
+ *
+ * If we wanted to unmap freed LDTs, we'd also need to do a flush to make
+ * it useful, and the flush would slow down modify_ldt().
+ */
+static int
+map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
+{
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ bool is_vmalloc, had_top_level_entry;
+ unsigned long va;
+ spinlock_t *ptl;
+ pgd_t *pgd;
+ int i;
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return 0;
+
+ /*
+ * Any given ldt_struct should have map_ldt_struct() called at most
+ * once.
+ */
+ WARN_ON(ldt->slot != -1);
+
+ /*
+ * Did we already have the top level entry allocated? We can't
+ * use pgd_none() for this because it doens't do anything on
+ * 4-level page table kernels.
+ */
+ pgd = pgd_offset(mm, LDT_BASE_ADDR);
+ had_top_level_entry = (pgd->pgd != 0);
+
+ is_vmalloc = is_vmalloc_addr(ldt->entries);
+
+ for (i = 0; i * PAGE_SIZE < ldt->nr_entries * LDT_ENTRY_SIZE; i++) {
+ unsigned long offset = i << PAGE_SHIFT;
+ const void *src = (char *)ldt->entries + offset;
+ unsigned long pfn;
+ pte_t pte, *ptep;
+
+ va = (unsigned long)ldt_slot_va(slot) + offset;
+ pfn = is_vmalloc ? vmalloc_to_pfn(src) :
+ page_to_pfn(virt_to_page(src));
+ /*
+ * Treat the PTI LDT range as a *userspace* range.
+ * get_locked_pte() will allocate all needed pagetables
+ * and account for them in this mm.
+ */
+ ptep = get_locked_pte(mm, va, &ptl);
+ if (!ptep)
+ return -ENOMEM;
+ pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL));
+ set_pte_at(mm, va, ptep, pte);
+ pte_unmap_unlock(ptep, ptl);
+ }
+
+ if (mm->context.ldt) {
+ /*
+ * We already had an LDT. The top-level entry should already
+ * have been allocated and synchronized with the usermode
+ * tables.
+ */
+ WARN_ON(!had_top_level_entry);
+ if (static_cpu_has(X86_FEATURE_PTI))
+ WARN_ON(!kernel_to_user_pgdp(pgd)->pgd);
+ } else {
+ /*
+ * This is the first time we're mapping an LDT for this process.
+ * Sync the pgd to the usermode tables.
+ */
+ WARN_ON(had_top_level_entry);
+ if (static_cpu_has(X86_FEATURE_PTI)) {
+ WARN_ON(kernel_to_user_pgdp(pgd)->pgd);
+ set_pgd(kernel_to_user_pgdp(pgd), *pgd);
+ }
+ }
+
+ va = (unsigned long)ldt_slot_va(slot);
+ flush_tlb_mm_range(mm, va, va + LDT_SLOT_STRIDE, 0);
+
+ ldt->slot = slot;
+#endif
+ return 0;
+}
+
+static void free_ldt_pgtables(struct mm_struct *mm)
+{
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ struct mmu_gather tlb;
+ unsigned long start = LDT_BASE_ADDR;
+ unsigned long end = start + (1UL << PGDIR_SHIFT);
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ tlb_gather_mmu(&tlb, mm, start, end);
+ free_pgd_range(&tlb, start, end, start, end);
+ tlb_finish_mmu(&tlb, start, end);
+#endif
+}
+