[PATCH v3.1 4/4] arm64: mm: Implement pte_devmap support

[Robin Murphy]

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.

Signed-off-by: Robin Murphy <robin.mur...@arm.com>
---

Fix to build correctly under all combinations of
CONFIG_PGTABLE_LEVELS and CONFIG_TRANSPARENT_HUGEPAGE.

 arch/arm64/Kconfig                    |  1 +
 arch/arm64/include/asm/pgtable-prot.h |  1 +
 arch/arm64/include/asm/pgtable.h      | 21 +++++++++++++++++++++
 3 files changed, 23 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 4780eb7af842..b5a4611fa4c6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -23,6 +23,7 @@ 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_MEMORY
diff --git a/arch/arm64/include/asm/pgtable-prot.h 
b/arch/arm64/include/asm/pgtable-prot.h
index 986e41c4c32b..af0b372d15e5 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -28,6 +28,7 @@
 #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 2c41b04708fe..7a2cf6939311 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -90,6 +90,7 @@ 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;    
\
@@ -217,6 +218,11 @@ 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);
@@ -381,6 +387,11 @@ 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)
@@ -666,6 +677,16 @@ 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
 
 /*
-- 
2.21.0.dirty