RISC-V: Paging and MMU

This patch contains code to manage the RISC-V MMU, including definitions
of the page tables and the page walking code.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

1 files changed, 430 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
new file mode 100644
index 000000000000..3399257780b2
--- /dev/null
+++ b/arch/riscv/include/asm/pgtable.h
@@ -0,0 +1,430 @@
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ */
+
+#ifndef _ASM_RISCV_PGTABLE_H
+#define _ASM_RISCV_PGTABLE_H
+
+#include <linux/mmzone.h>
+
+#include <asm/pgtable-bits.h>
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_MMU
+
+/* Page Upper Directory not used in RISC-V */
+#include <asm-generic/pgtable-nopud.h>
+#include <asm/page.h>
+#include <asm/tlbflush.h>
+#include <linux/mm_types.h>
+
+#ifdef CONFIG_64BIT
+#include <asm/pgtable-64.h>
+#else
+#include <asm/pgtable-32.h>
+#endif /* CONFIG_64BIT */
+
+/* Number of entries in the page global directory */
+#define PTRS_PER_PGD    (PAGE_SIZE / sizeof(pgd_t))
+/* Number of entries in the page table */
+#define PTRS_PER_PTE    (PAGE_SIZE / sizeof(pte_t))
+
+/* Number of PGD entries that a user-mode program can use */
+#define USER_PTRS_PER_PGD   (TASK_SIZE / PGDIR_SIZE)
+#define FIRST_USER_ADDRESS  0
+
+/* Page protection bits */
+#define _PAGE_BASE	(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER)
+
+#define PAGE_NONE		__pgprot(0)
+#define PAGE_READ		__pgprot(_PAGE_BASE | _PAGE_READ)
+#define PAGE_WRITE		__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_WRITE)
+#define PAGE_EXEC		__pgprot(_PAGE_BASE | _PAGE_EXEC)
+#define PAGE_READ_EXEC		__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_EXEC)
+#define PAGE_WRITE_EXEC		__pgprot(_PAGE_BASE | _PAGE_READ |	\
+					 _PAGE_EXEC | _PAGE_WRITE)
+
+#define PAGE_COPY		PAGE_READ
+#define PAGE_COPY_EXEC		PAGE_EXEC
+#define PAGE_COPY_READ_EXEC	PAGE_READ_EXEC
+#define PAGE_SHARED		PAGE_WRITE
+#define PAGE_SHARED_EXEC	PAGE_WRITE_EXEC
+
+#define _PAGE_KERNEL		(_PAGE_READ \
+				| _PAGE_WRITE \
+				| _PAGE_PRESENT \
+				| _PAGE_ACCESSED \
+				| _PAGE_DIRTY)
+
+#define PAGE_KERNEL		__pgprot(_PAGE_KERNEL)
+#define PAGE_KERNEL_EXEC	__pgprot(_PAGE_KERNEL | _PAGE_EXEC)
+
+extern pgd_t swapper_pg_dir[];
+
+/* MAP_PRIVATE permissions: xwr (copy-on-write) */
+#define __P000	PAGE_NONE
+#define __P001	PAGE_READ
+#define __P010	PAGE_COPY
+#define __P011	PAGE_COPY
+#define __P100	PAGE_EXEC
+#define __P101	PAGE_READ_EXEC
+#define __P110	PAGE_COPY_EXEC
+#define __P111	PAGE_COPY_READ_EXEC
+
+/* MAP_SHARED permissions: xwr */
+#define __S000	PAGE_NONE
+#define __S001	PAGE_READ
+#define __S010	PAGE_SHARED
+#define __S011	PAGE_SHARED
+#define __S100	PAGE_EXEC
+#define __S101	PAGE_READ_EXEC
+#define __S110	PAGE_SHARED_EXEC
+#define __S111	PAGE_SHARED_EXEC
+
+/*
+ * ZERO_PAGE is a global shared page that is always zero,
+ * used for zero-mapped memory areas, etc.
+ */
+extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
+#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
+
+static inline int pmd_present(pmd_t pmd)
+{
+	return (pmd_val(pmd) & _PAGE_PRESENT);
+}
+
+static inline int pmd_none(pmd_t pmd)
+{
+	return (pmd_val(pmd) == 0);
+}
+
+static inline int pmd_bad(pmd_t pmd)
+{
+	return !pmd_present(pmd);
+}
+
+static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
+{
+	*pmdp = pmd;
+}
+
+static inline void pmd_clear(pmd_t *pmdp)
+{
+	set_pmd(pmdp, __pmd(0));
+}
+
+
+static inline pgd_t pfn_pgd(unsigned long pfn, pgprot_t prot)
+{
+	return __pgd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+}
+
+#define pgd_index(addr) (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
+
+/* Locate an entry in the page global directory */
+static inline pgd_t *pgd_offset(const struct mm_struct *mm, unsigned long addr)
+{
+	return mm->pgd + pgd_index(addr);
+}
+/* Locate an entry in the kernel page global directory */
+#define pgd_offset_k(addr)      pgd_offset(&init_mm, (addr))
+
+static inline struct page *pmd_page(pmd_t pmd)
+{
+	return pfn_to_page(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
+}
+
+static inline unsigned long pmd_page_vaddr(pmd_t pmd)
+{
+	return (unsigned long)pfn_to_virt(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
+}
+
+/* Yields the page frame number (PFN) of a page table entry */
+static inline unsigned long pte_pfn(pte_t pte)
+{
+	return (pte_val(pte) >> _PAGE_PFN_SHIFT);
+}
+
+#define pte_page(x)     pfn_to_page(pte_pfn(x))
+
+/* Constructs a page table entry */
+static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
+{
+	return __pte((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
+}
+
+static inline pte_t mk_pte(struct page *page, pgprot_t prot)
+{
+	return pfn_pte(page_to_pfn(page), prot);
+}
+
+#define pte_index(addr) (((addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1))
+
+static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long addr)
+{
+	return (pte_t *)pmd_page_vaddr(*pmd) + pte_index(addr);
+}
+
+#define pte_offset_map(dir, addr)	pte_offset_kernel((dir), (addr))
+#define pte_unmap(pte)			((void)(pte))
+
+/*
+ * Certain architectures need to do special things when PTEs within
+ * a page table are directly modified.  Thus, the following hook is
+ * made available.
+ */
+static inline void set_pte(pte_t *ptep, pte_t pteval)
+{
+	*ptep = pteval;
+}
+
+static inline void set_pte_at(struct mm_struct *mm,
+	unsigned long addr, pte_t *ptep, pte_t pteval)
+{
+	set_pte(ptep, pteval);
+}
+
+static inline void pte_clear(struct mm_struct *mm,
+	unsigned long addr, pte_t *ptep)
+{
+	set_pte_at(mm, addr, ptep, __pte(0));
+}
+
+static inline int pte_present(pte_t pte)
+{
+	return (pte_val(pte) & _PAGE_PRESENT);
+}
+
+static inline int pte_none(pte_t pte)
+{
+	return (pte_val(pte) == 0);
+}
+
+/* static inline int pte_read(pte_t pte) */
+
+static inline int pte_write(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_WRITE;
+}
+
+static inline int pte_huge(pte_t pte)
+{
+	return pte_present(pte)
+		&& (pte_val(pte) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+}
+
+/* static inline int pte_exec(pte_t pte) */
+
+static inline int pte_dirty(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_DIRTY;
+}
+
+static inline int pte_young(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_ACCESSED;
+}
+
+static inline int pte_special(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SPECIAL;
+}
+
+/* static inline pte_t pte_rdprotect(pte_t pte) */
+
+static inline pte_t pte_wrprotect(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~(_PAGE_WRITE));
+}
+
+/* static inline pte_t pte_mkread(pte_t pte) */
+
+static inline pte_t pte_mkwrite(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_WRITE);
+}
+
+/* static inline pte_t pte_mkexec(pte_t pte) */
+
+static inline pte_t pte_mkdirty(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_DIRTY);
+}
+
+static inline pte_t pte_mkclean(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~(_PAGE_DIRTY));
+}
+
+static inline pte_t pte_mkyoung(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_ACCESSED);
+}
+
+static inline pte_t pte_mkold(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~(_PAGE_ACCESSED));
+}
+
+static inline pte_t pte_mkspecial(pte_t pte)
+{
+	return __pte(pte_val(pte) | _PAGE_SPECIAL);
+}
+
+/* Modify page protection bits */
+static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
+{
+	return __pte((pte_val(pte) & _PAGE_CHG_MASK) | pgprot_val(newprot));
+}
+
+#define pgd_ERROR(e) \
+	pr_err("%s:%d: bad pgd " PTE_FMT ".\n", __FILE__, __LINE__, pgd_val(e))
+
+
+/* Commit new configuration to MMU hardware */
+static inline void update_mmu_cache(struct vm_area_struct *vma,
+	unsigned long address, pte_t *ptep)
+{
+	/*
+	 * The kernel assumes that TLBs don't cache invalid entries, but
+	 * in RISC-V, SFENCE.VMA specifies an ordering constraint, not a
+	 * cache flush; it is necessary even after writing invalid entries.
+	 * Relying on flush_tlb_fix_spurious_fault would suffice, but
+	 * the extra traps reduce performance.  So, eagerly SFENCE.VMA.
+	 */
+	local_flush_tlb_page(address);
+}
+
+#define __HAVE_ARCH_PTE_SAME
+static inline int pte_same(pte_t pte_a, pte_t pte_b)
+{
+	return pte_val(pte_a) == pte_val(pte_b);
+}
+
+#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
+static inline int ptep_set_access_flags(struct vm_area_struct *vma,
+					unsigned long address, pte_t *ptep,
+					pte_t entry, int dirty)
+{
+	if (!pte_same(*ptep, entry))
+		set_pte_at(vma->vm_mm, address, ptep, entry);
+	/*
+	 * update_mmu_cache will unconditionally execute, handling both
+	 * the case that the PTE changed and the spurious fault case.
+	 */
+	return true;
+}
+
+#define __HAVE_ARCH_PTEP_GET_AND_CLEAR
+static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
+				       unsigned long address, pte_t *ptep)
+{
+	return __pte(atomic_long_xchg((atomic_long_t *)ptep, 0));
+}
+
+#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
+static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
+					    unsigned long address,
+					    pte_t *ptep)
+{
+	if (!pte_young(*ptep))
+		return 0;
+	return test_and_clear_bit(_PAGE_ACCESSED_OFFSET, &pte_val(*ptep));
+}
+
+#define __HAVE_ARCH_PTEP_SET_WRPROTECT
+static inline void ptep_set_wrprotect(struct mm_struct *mm,
+				      unsigned long address, pte_t *ptep)
+{
+	atomic_long_and(~(unsigned long)_PAGE_WRITE, (atomic_long_t *)ptep);
+}
+
+#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
+static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
+					 unsigned long address, pte_t *ptep)
+{
+	/*
+	 * This comment is borrowed from x86, but applies equally to RISC-V:
+	 *
+	 * Clearing the accessed bit without a TLB flush
+	 * doesn't cause data corruption. [ It could cause incorrect
+	 * page aging and the (mistaken) reclaim of hot pages, but the
+	 * chance of that should be relatively low. ]
+	 *
+	 * So as a performance optimization don't flush the TLB when
+	 * clearing the accessed bit, it will eventually be flushed by
+	 * a context switch or a VM operation anyway. [ In the rare
+	 * event of it not getting flushed for a long time the delay
+	 * shouldn't really matter because there's no real memory
+	 * pressure for swapout to react to. ]
+	 */
+	return ptep_test_and_clear_young(vma, address, ptep);
+}
+
+/*
+ * Encode and decode a swap entry
+ *
+ * Format of swap PTE:
+ *	bit            0:	_PAGE_PRESENT (zero)
+ *	bit            1:	reserved for future use (zero)
+ *	bits      2 to 6:	swap type
+ *	bits 7 to XLEN-1:	swap offset
+ */
+#define __SWP_TYPE_SHIFT	2
+#define __SWP_TYPE_BITS		5
+#define __SWP_TYPE_MASK		((1UL << __SWP_TYPE_BITS) - 1)
+#define __SWP_OFFSET_SHIFT	(__SWP_TYPE_BITS + __SWP_TYPE_SHIFT)
+
+#define MAX_SWAPFILES_CHECK()	\
+	BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > __SWP_TYPE_BITS)
+
+#define __swp_type(x)	(((x).val >> __SWP_TYPE_SHIFT) & __SWP_TYPE_MASK)
+#define __swp_offset(x)	((x).val >> __SWP_OFFSET_SHIFT)
+#define __swp_entry(type, offset) ((swp_entry_t) \
+	{ ((type) << __SWP_TYPE_SHIFT) | ((offset) << __SWP_OFFSET_SHIFT) })
+
+#define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) })
+#define __swp_entry_to_pte(x)	((pte_t) { (x).val })
+
+#ifdef CONFIG_FLATMEM
+#define kern_addr_valid(addr)   (1) /* FIXME */
+#endif
+
+extern void paging_init(void);
+
+static inline void pgtable_cache_init(void)
+{
+	/* No page table caches to initialize */
+}
+
+#endif /* CONFIG_MMU */
+
+#define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
+#define VMALLOC_END      (PAGE_OFFSET - 1)
+#define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
+
+/*
+ * Task size is 0x40000000000 for RV64 or 0xb800000 for RV32.
+ * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
+ */
+#ifdef CONFIG_64BIT
+#define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)
+#else
+#define TASK_SIZE VMALLOC_START
+#endif
+
+#include <asm-generic/pgtable.h>
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* _ASM_RISCV_PGTABLE_H */