[PATCH v3 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.murphy@xxxxxxx>
---
 arch/arm64/Kconfig                    |  1 +
 arch/arm64/include/asm/pgtable-prot.h |  1 +
 arch/arm64/include/asm/pgtable.h      | 19 +++++++++++++++++++
 3 files changed, 21 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..a6378625d47c 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 +387,9 @@ static inline int pmd_protnone(pmd_t pmd)
 
 #define pmd_mkhuge(pmd)		(__pmd(pmd_val(pmd) & ~PMD_TABLE_BIT))
 
+#define pmd_devmap(pmd)		pte_devmap(pmd_pte(pmd))
+#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)
@@ -537,6 +546,11 @@ static inline phys_addr_t pud_page_paddr(pud_t pud)
 	return __pud_to_phys(pud);
 }
 
+static inline int pud_devmap(pud_t pud)
+{
+	return 0;
+}
+
 /* Find an entry in the second-level page table. */
 #define pmd_index(addr)		(((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1))
 
@@ -624,6 +638,11 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
 
 #define pgd_ERROR(pgd)		__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
 
+static inline int pgd_devmap(pgd_t pgd)
+{
+	return 0;
+}
+
 /* to find an entry in a page-table-directory */
 #define pgd_index(addr)		(((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
 
-- 
2.21.0.dirty