arm64: mm: implement pte_devmap support

In order for things like get_user_pages() to work on ZONE_DEVICE memory,
we need a software PTE bit to identify device-backed PFNs.  Hook this up
along with the relevant helpers to join in with ARCH_HAS_PTE_DEVMAP.

[robin.murphy@arm.com: build fixes]
  Link: http://lkml.kernel.org/r/13026c4e64abc17133bbfa07d7731ec6691c0bcd.1559050949.git.robin.murphy@arm.com
Link: http://lkml.kernel.org/r/817d92886fc3b33bcbf6e105ee83a74babb3a5aa.1558547956.git.robin.murphy@arm.com
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 23 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a36ff61321ce..0758d89524d0 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -24,6 +24,7 @@ config ARM64
         select ARCH_HAS_KCOV
         select ARCH_HAS_KEEPINITRD
         select ARCH_HAS_MEMBARRIER_SYNC_CORE
+        select ARCH_HAS_PTE_DEVMAP
         select ARCH_HAS_PTE_SPECIAL
         select ARCH_HAS_SETUP_DMA_OPS
         select ARCH_HAS_SET_DIRECT_MAP
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index f318258a14be..92d2e9f28f28 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -16,6 +16,7 @@
 #define PTE_WRITE               (PTE_DBM)                /* same as DBM (51) */
 #define PTE_DIRTY               (_AT(pteval_t, 1) << 55)
 #define PTE_SPECIAL             (_AT(pteval_t, 1) << 56)
+#define PTE_DEVMAP              (_AT(pteval_t, 1) << 57)
 #define PTE_PROT_NONE           (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
 
 #ifndef __ASSEMBLY__
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 3052381baaeb..87a4b2ddc1a1 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -79,6 +79,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define pte_write(pte)          (!!(pte_val(pte) & PTE_WRITE))
 #define pte_user_exec(pte)      (!(pte_val(pte) & PTE_UXN))
 #define pte_cont(pte)           (!!(pte_val(pte) & PTE_CONT))
+#define pte_devmap(pte)         (!!(pte_val(pte) & PTE_DEVMAP))
 
 #define pte_cont_addr_end(addr, end)                                            \
 ({      unsigned long __boundary = ((addr) + CONT_PTE_SIZE) & CONT_PTE_MASK;    \
@@ -206,6 +207,11 @@ static inline pmd_t pmd_mkcont(pmd_t pmd)
         return __pmd(pmd_val(pmd) | PMD_SECT_CONT);
 }
 
+static inline pte_t pte_mkdevmap(pte_t pte)
+{
+        return set_pte_bit(pte, __pgprot(PTE_DEVMAP));
+}
+
 static inline void set_pte(pte_t *ptep, pte_t pte)
 {
         WRITE_ONCE(*ptep, pte);
@@ -388,6 +394,11 @@ static inline int pmd_protnone(pmd_t pmd)
 
 #define pmd_mkhuge(pmd)         (__pmd(pmd_val(pmd) & ~PMD_TABLE_BIT))
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define pmd_devmap(pmd)         pte_devmap(pmd_pte(pmd))
+#endif
+#define pmd_mkdevmap(pmd)       pte_pmd(pte_mkdevmap(pmd_pte(pmd)))
+
 #define __pmd_to_phys(pmd)      __pte_to_phys(pmd_pte(pmd))
 #define __phys_to_pmd_val(phys) __phys_to_pte_val(phys)
 #define pmd_pfn(pmd)            ((__pmd_to_phys(pmd) & PMD_MASK) >> PAGE_SHIFT)
@@ -673,6 +684,16 @@ static inline int pmdp_set_access_flags(struct vm_area_struct *vma,
 {
         return ptep_set_access_flags(vma, address, (pte_t *)pmdp, pmd_pte(entry), dirty);
 }
+
+static inline int pud_devmap(pud_t pud)
+{
+        return 0;
+}
+
+static inline int pgd_devmap(pgd_t pgd)
+{
+        return 0;
+}
 #endif
 
 /*