[PATCH v31 04/12] arm64: mm: allow for unmapping part of kernel mapping

AKASHI Takahiro
2017-02-01T12:46:23Z

A new function, remove_pgd_mapping(), is added.
It allows us to unmap a specific portion of kernel mapping later as far as
the mapping is made using create_pgd_mapping() and unless we try to free
a sub-set of memory range within a section mapping.

This function will be used in a later kdump patch to implement
the protection against corrupting crash dump kernel memory which is to be
set aside.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
arch/arm64/include/asm/mmu.h | 2 +
arch/arm64/mm/mmu.c | 130 +++++++++++++++++++++++++++++++++++++++++--
2 files changed, 127 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 47619411f0ff..04eb240736d8 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -36,6 +36,8 @@ extern void init_mem_pgprot(void);
extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
unsigned long virt, phys_addr_t size,
pgprot_t prot, bool page_mappings_only);
+extern void remove_pgd_mapping(struct mm_struct *mm, unsigned long virt,
+ phys_addr_t size);
extern void *fixmap_remap_fdt(phys_addr_t dt_phys);

#endif
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 17243e43184e..9d3cea1db3b4 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -334,12 +334,10 @@ static void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
__create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, false);
}

-void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
- unsigned long virt, phys_addr_t size,
- pgprot_t prot, bool page_mappings_only)
+void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
+ unsigned long virt, phys_addr_t size,
+ pgprot_t prot, bool page_mappings_only)
{
- BUG_ON(mm == &init_mm);
-
__create_pgd_mapping(mm->pgd, phys, virt, size, prot,
pgd_pgtable_alloc, page_mappings_only);
}
@@ -357,6 +355,128 @@ static void create_mapping_late(phys_addr_t phys, unsigned long virt,
NULL, debug_pagealloc_enabled());
}

+static bool pgtable_is_cleared(void *pgtable)
+{
+ unsigned long *desc, *end;
+
+ for (desc = pgtable, end = (unsigned long *)(pgtable + PAGE_SIZE);
+ desc < end; desc++)
+ if (*desc)
+ return false;
+
+ return true;
+}
+
+static void clear_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end)
+{
+ pte_t *pte;
+
+ if (WARN_ON(pmd_bad(*pmd)))
+ return;
+
+ pte = pte_set_fixmap_offset(pmd, addr);
+
+ do {
+ pte_clear(NULL, NULL, pte);
+ } while (pte++, addr += PAGE_SIZE, addr != end);
+
+ pte_clear_fixmap();
+}
+
+static void clear_pmd_range(pud_t *pud, unsigned long addr, unsigned long end)
+{
+ pmd_t *pmd;
+ unsigned long next;
+
+ if (WARN_ON(pud_bad(*pud)))
+ return;
+
+ pmd = pmd_set_fixmap_offset(pud, addr);
+
+ do {
+ next = pmd_addr_end(addr, end);
+
+ if (pmd_table(*pmd)) {
+ clear_pte_range(pmd, addr, next);
+ if (((next - addr) == PMD_SIZE) ||
+ pgtable_is_cleared(__va(pmd_page_paddr(*pmd)))) {
+ __free_page(pmd_page(*pmd));
+ pmd_clear(pmd);
+ }
+ } else {
+ if (WARN_ON((next - addr) != PMD_SIZE))
+ return;
+ pmd_clear(pmd);
+ }
+ } while (pmd++, addr = next, addr != end);
+
+ pmd_clear_fixmap();
+}
+
+static void clear_pud_range(pgd_t *pgd, unsigned long addr, unsigned long end)
+{
+ pud_t *pud;
+ unsigned long next;
+
+ if (WARN_ON(pgd_bad(*pgd)))
+ return;
+
+ pud = pud_set_fixmap_offset(pgd, addr);
+
+ do {
+ next = pud_addr_end(addr, end);
+
+ if (pud_table(*pud)) {
+ clear_pmd_range(pud, addr, next);
+#if CONFIG_PGTABLE_LEVELS > 2
+ if (((next - addr) == PUD_SIZE) ||
+ pgtable_is_cleared(__va(pud_page_paddr(*pud)))) {
+ __free_page(pud_page(*pud));
+ pud_clear(pud);
+ }
+#endif
+ } else {
+#if CONFIG_PGTABLE_LEVELS > 2
+ if (WARN_ON((next - addr) != PUD_SIZE))
+ return;
+ pud_clear(pud);
+#endif
+ }
+ } while (pud++, addr = next, addr != end);
+
+ pud_clear_fixmap();
+}
+
+static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long virt,
+ phys_addr_t size)
+{
+ unsigned long addr, length, end, next;
+ pgd_t *pgd = pgd_offset_raw(pgdir, virt);
+
+ addr = virt & PAGE_MASK;
+ length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));
+
+ end = addr + length;
+ do {
+ next = pgd_addr_end(addr, end);
+ clear_pud_range(pgd, addr, next);
+
+#if CONFIG_PGTABLE_LEVELS > 3
+ if (((next - addr) == PGD_SIZE) ||
+ pgtable_is_cleared(__va(pgd_page_paddr(*pgd)))) {
+ __free_page(pgd_page(*pgd));
+ pgd_clear(pgd);
+ }
+#endif
+ } while (pgd++, addr = next, addr != end);
+}
+
+void remove_pgd_mapping(struct mm_struct *mm, unsigned long virt,
+ phys_addr_t size)
+{
+ __remove_pgd_mapping(mm->pgd, virt, size);
+}
+
static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end)
{
unsigned long kernel_start = __pa(_text);
--
2.11.0