riscv: Implement sv48 support

By adding a new 4th level of page table, give the possibility to 64bit
kernel to address 2^48 bytes of virtual address: in practice, that offers
128TB of virtual address space to userspace and allows up to 64TB of
physical memory.

If the underlying hardware does not support sv48, we will automatically
fallback to a standard 3-level page table by folding the new PUD level into
PGDIR level. In order to detect HW capabilities at runtime, we
use SATP feature that ignores writes with an unsupported mode.

Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 188 insertions, 24 deletions

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 424d7777f4df..7ba915849817 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -37,6 +37,17 @@ EXPORT_SYMBOL(kernel_map);
 #define kernel_map	(*(struct kernel_mapping *)XIP_FIXUP(&kernel_map))
 #endif
 
+#ifdef CONFIG_64BIT
+u64 satp_mode = !IS_ENABLED(CONFIG_XIP_KERNEL) ? SATP_MODE_48 : SATP_MODE_39;
+#else
+u64 satp_mode = SATP_MODE_32;
+#endif
+EXPORT_SYMBOL(satp_mode);
+
+bool pgtable_l4_enabled = IS_ENABLED(CONFIG_64BIT) && !IS_ENABLED(CONFIG_XIP_KERNEL) ?
+				true : false;
+EXPORT_SYMBOL(pgtable_l4_enabled);
+
 phys_addr_t phys_ram_base __ro_after_init;
 EXPORT_SYMBOL(phys_ram_base);
 
@@ -53,15 +64,6 @@ extern char _start[];
 void *_dtb_early_va __initdata;
 uintptr_t _dtb_early_pa __initdata;
 
-struct pt_alloc_ops {
-	pte_t *(*get_pte_virt)(phys_addr_t pa);
-	phys_addr_t (*alloc_pte)(uintptr_t va);
-#ifndef __PAGETABLE_PMD_FOLDED
-	pmd_t *(*get_pmd_virt)(phys_addr_t pa);
-	phys_addr_t (*alloc_pmd)(uintptr_t va);
-#endif
-};
-
 static phys_addr_t dma32_phys_limit __initdata;
 
 static void __init zone_sizes_init(void)
@@ -222,7 +224,7 @@ static void __init setup_bootmem(void)
 }
 
 #ifdef CONFIG_MMU
-static struct pt_alloc_ops _pt_ops __initdata;
+struct pt_alloc_ops _pt_ops __initdata;
 
 #ifdef CONFIG_XIP_KERNEL
 #define pt_ops (*(struct pt_alloc_ops *)XIP_FIXUP(&_pt_ops))
@@ -238,6 +240,7 @@ pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 static pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
 
 pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
+static pud_t __maybe_unused early_dtb_pud[PTRS_PER_PUD] __initdata __aligned(PAGE_SIZE);
 static pmd_t __maybe_unused early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
 
 #ifdef CONFIG_XIP_KERNEL
@@ -326,6 +329,16 @@ static pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
 #define early_pmd      ((pmd_t *)XIP_FIXUP(early_pmd))
 #endif /* CONFIG_XIP_KERNEL */
 
+static pud_t trampoline_pud[PTRS_PER_PUD] __page_aligned_bss;
+static pud_t fixmap_pud[PTRS_PER_PUD] __page_aligned_bss;
+static pud_t early_pud[PTRS_PER_PUD] __initdata __aligned(PAGE_SIZE);
+
+#ifdef CONFIG_XIP_KERNEL
+#define trampoline_pud ((pud_t *)XIP_FIXUP(trampoline_pud))
+#define fixmap_pud     ((pud_t *)XIP_FIXUP(fixmap_pud))
+#define early_pud      ((pud_t *)XIP_FIXUP(early_pud))
+#endif /* CONFIG_XIP_KERNEL */
+
 static pmd_t *__init get_pmd_virt_early(phys_addr_t pa)
 {
 	/* Before MMU is enabled */
@@ -345,7 +358,7 @@ static pmd_t *__init get_pmd_virt_late(phys_addr_t pa)
 
 static phys_addr_t __init alloc_pmd_early(uintptr_t va)
 {
-	BUG_ON((va - kernel_map.virt_addr) >> PGDIR_SHIFT);
+	BUG_ON((va - kernel_map.virt_addr) >> PUD_SHIFT);
 
 	return (uintptr_t)early_pmd;
 }
@@ -391,21 +404,97 @@ static void __init create_pmd_mapping(pmd_t *pmdp,
 	create_pte_mapping(ptep, va, pa, sz, prot);
 }
 
-#define pgd_next_t		pmd_t
-#define alloc_pgd_next(__va)	pt_ops.alloc_pmd(__va)
-#define get_pgd_next_virt(__pa)	pt_ops.get_pmd_virt(__pa)
+static pud_t *__init get_pud_virt_early(phys_addr_t pa)
+{
+	return (pud_t *)((uintptr_t)pa);
+}
+
+static pud_t *__init get_pud_virt_fixmap(phys_addr_t pa)
+{
+	clear_fixmap(FIX_PUD);
+	return (pud_t *)set_fixmap_offset(FIX_PUD, pa);
+}
+
+static pud_t *__init get_pud_virt_late(phys_addr_t pa)
+{
+	return (pud_t *)__va(pa);
+}
+
+static phys_addr_t __init alloc_pud_early(uintptr_t va)
+{
+	/* Only one PUD is available for early mapping */
+	BUG_ON((va - kernel_map.virt_addr) >> PGDIR_SHIFT);
+
+	return (uintptr_t)early_pud;
+}
+
+static phys_addr_t __init alloc_pud_fixmap(uintptr_t va)
+{
+	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
+}
+
+static phys_addr_t alloc_pud_late(uintptr_t va)
+{
+	unsigned long vaddr;
+
+	vaddr = __get_free_page(GFP_KERNEL);
+	BUG_ON(!vaddr);
+	return __pa(vaddr);
+}
+
+static void __init create_pud_mapping(pud_t *pudp,
+				      uintptr_t va, phys_addr_t pa,
+				      phys_addr_t sz, pgprot_t prot)
+{
+	pmd_t *nextp;
+	phys_addr_t next_phys;
+	uintptr_t pud_index = pud_index(va);
+
+	if (sz == PUD_SIZE) {
+		if (pud_val(pudp[pud_index]) == 0)
+			pudp[pud_index] = pfn_pud(PFN_DOWN(pa), prot);
+		return;
+	}
+
+	if (pud_val(pudp[pud_index]) == 0) {
+		next_phys = pt_ops.alloc_pmd(va);
+		pudp[pud_index] = pfn_pud(PFN_DOWN(next_phys), PAGE_TABLE);
+		nextp = pt_ops.get_pmd_virt(next_phys);
+		memset(nextp, 0, PAGE_SIZE);
+	} else {
+		next_phys = PFN_PHYS(_pud_pfn(pudp[pud_index]));
+		nextp = pt_ops.get_pmd_virt(next_phys);
+	}
+
+	create_pmd_mapping(nextp, va, pa, sz, prot);
+}
+
+#define pgd_next_t		pud_t
+#define alloc_pgd_next(__va)	(pgtable_l4_enabled ?			\
+		pt_ops.alloc_pud(__va) : pt_ops.alloc_pmd(__va))
+#define get_pgd_next_virt(__pa)	(pgtable_l4_enabled ?			\
+		pt_ops.get_pud_virt(__pa) : (pgd_next_t *)pt_ops.get_pmd_virt(__pa))
 #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)	\
-	create_pmd_mapping(__nextp, __va, __pa, __sz, __prot)
-#define fixmap_pgd_next		fixmap_pmd
+				(pgtable_l4_enabled ?			\
+		create_pud_mapping(__nextp, __va, __pa, __sz, __prot) :	\
+		create_pmd_mapping((pmd_t *)__nextp, __va, __pa, __sz, __prot))
+#define fixmap_pgd_next		(pgtable_l4_enabled ?			\
+		(uintptr_t)fixmap_pud : (uintptr_t)fixmap_pmd)
+#define trampoline_pgd_next	(pgtable_l4_enabled ?			\
+		(uintptr_t)trampoline_pud : (uintptr_t)trampoline_pmd)
+#define early_dtb_pgd_next	(pgtable_l4_enabled ?			\
+		(uintptr_t)early_dtb_pud : (uintptr_t)early_dtb_pmd)
 #else
 #define pgd_next_t		pte_t
 #define alloc_pgd_next(__va)	pt_ops.alloc_pte(__va)
 #define get_pgd_next_virt(__pa)	pt_ops.get_pte_virt(__pa)
 #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)	\
 	create_pte_mapping(__nextp, __va, __pa, __sz, __prot)
-#define fixmap_pgd_next		fixmap_pte
+#define fixmap_pgd_next		((uintptr_t)fixmap_pte)
+#define early_dtb_pgd_next	((uintptr_t)early_dtb_pmd)
+#define create_pud_mapping(__pmdp, __va, __pa, __sz, __prot)
 #define create_pmd_mapping(__pmdp, __va, __pa, __sz, __prot)
-#endif
+#endif /* __PAGETABLE_PMD_FOLDED */
 
 void __init create_pgd_mapping(pgd_t *pgdp,
 				      uintptr_t va, phys_addr_t pa,
@@ -492,6 +581,57 @@ static __init pgprot_t pgprot_from_va(uintptr_t va)
 }
 #endif /* CONFIG_STRICT_KERNEL_RWX */
 
+#ifdef CONFIG_64BIT
+static void __init disable_pgtable_l4(void)
+{
+	pgtable_l4_enabled = false;
+	kernel_map.page_offset = PAGE_OFFSET_L3;
+	satp_mode = SATP_MODE_39;
+}
+
+/*
+ * There is a simple way to determine if 4-level is supported by the
+ * underlying hardware: establish 1:1 mapping in 4-level page table mode
+ * then read SATP to see if the configuration was taken into account
+ * meaning sv48 is supported.
+ */
+static __init void set_satp_mode(void)
+{
+	u64 identity_satp, hw_satp;
+	uintptr_t set_satp_mode_pmd;
+
+	set_satp_mode_pmd = ((unsigned long)set_satp_mode) & PMD_MASK;
+	create_pgd_mapping(early_pg_dir,
+			   set_satp_mode_pmd, (uintptr_t)early_pud,
+			   PGDIR_SIZE, PAGE_TABLE);
+	create_pud_mapping(early_pud,
+			   set_satp_mode_pmd, (uintptr_t)early_pmd,
+			   PUD_SIZE, PAGE_TABLE);
+	/* Handle the case where set_satp_mode straddles 2 PMDs */
+	create_pmd_mapping(early_pmd,
+			   set_satp_mode_pmd, set_satp_mode_pmd,
+			   PMD_SIZE, PAGE_KERNEL_EXEC);
+	create_pmd_mapping(early_pmd,
+			   set_satp_mode_pmd + PMD_SIZE,
+			   set_satp_mode_pmd + PMD_SIZE,
+			   PMD_SIZE, PAGE_KERNEL_EXEC);
+
+	identity_satp = PFN_DOWN((uintptr_t)&early_pg_dir) | satp_mode;
+
+	local_flush_tlb_all();
+	csr_write(CSR_SATP, identity_satp);
+	hw_satp = csr_swap(CSR_SATP, 0ULL);
+	local_flush_tlb_all();
+
+	if (hw_satp != identity_satp)
+		disable_pgtable_l4();
+
+	memset(early_pg_dir, 0, PAGE_SIZE);
+	memset(early_pud, 0, PAGE_SIZE);
+	memset(early_pmd, 0, PAGE_SIZE);
+}
+#endif
+
 /*
  * setup_vm() is called from head.S with MMU-off.
  *
@@ -556,10 +696,15 @@ static void __init create_fdt_early_page_table(pgd_t *pgdir, uintptr_t dtb_pa)
 	uintptr_t pa = dtb_pa & ~(PMD_SIZE - 1);
 
 	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
-			   IS_ENABLED(CONFIG_64BIT) ? (uintptr_t)early_dtb_pmd : pa,
+			   IS_ENABLED(CONFIG_64BIT) ? early_dtb_pgd_next : pa,
 			   PGDIR_SIZE,
 			   IS_ENABLED(CONFIG_64BIT) ? PAGE_TABLE : PAGE_KERNEL);
 
+	if (pgtable_l4_enabled) {
+		create_pud_mapping(early_dtb_pud, DTB_EARLY_BASE_VA,
+				   (uintptr_t)early_dtb_pmd, PUD_SIZE, PAGE_TABLE);
+	}
+
 	if (IS_ENABLED(CONFIG_64BIT)) {
 		create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA,
 				   pa, PMD_SIZE, PAGE_KERNEL);
@@ -592,6 +737,8 @@ void pt_ops_set_early(void)
 #ifndef __PAGETABLE_PMD_FOLDED
 	pt_ops.alloc_pmd = alloc_pmd_early;
 	pt_ops.get_pmd_virt = get_pmd_virt_early;
+	pt_ops.alloc_pud = alloc_pud_early;
+	pt_ops.get_pud_virt = get_pud_virt_early;
 #endif
 }
 
@@ -610,6 +757,8 @@ void pt_ops_set_fixmap(void)
 #ifndef __PAGETABLE_PMD_FOLDED
 	pt_ops.alloc_pmd = kernel_mapping_pa_to_va((uintptr_t)alloc_pmd_fixmap);
 	pt_ops.get_pmd_virt = kernel_mapping_pa_to_va((uintptr_t)get_pmd_virt_fixmap);
+	pt_ops.alloc_pud = kernel_mapping_pa_to_va((uintptr_t)alloc_pud_fixmap);
+	pt_ops.get_pud_virt = kernel_mapping_pa_to_va((uintptr_t)get_pud_virt_fixmap);
 #endif
 }
 
@@ -624,6 +773,8 @@ void pt_ops_set_late(void)
 #ifndef __PAGETABLE_PMD_FOLDED
 	pt_ops.alloc_pmd = alloc_pmd_late;
 	pt_ops.get_pmd_virt = get_pmd_virt_late;
+	pt_ops.alloc_pud = alloc_pud_late;
+	pt_ops.get_pud_virt = get_pud_virt_late;
 #endif
 }
 
@@ -632,6 +783,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	pmd_t __maybe_unused fix_bmap_spmd, fix_bmap_epmd;
 
 	kernel_map.virt_addr = KERNEL_LINK_ADDR;
+	kernel_map.page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
 
 #ifdef CONFIG_XIP_KERNEL
 	kernel_map.xiprom = (uintptr_t)CONFIG_XIP_PHYS_ADDR;
@@ -646,6 +798,11 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	kernel_map.phys_addr = (uintptr_t)(&_start);
 	kernel_map.size = (uintptr_t)(&_end) - kernel_map.phys_addr;
 #endif
+
+#if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
+	set_satp_mode();
+#endif
+
 	kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
 	kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr;
 
@@ -675,15 +832,21 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 	/* Setup early PGD for fixmap */
 	create_pgd_mapping(early_pg_dir, FIXADDR_START,
-			   (uintptr_t)fixmap_pgd_next, PGDIR_SIZE, PAGE_TABLE);
+			   fixmap_pgd_next, PGDIR_SIZE, PAGE_TABLE);
 
 #ifndef __PAGETABLE_PMD_FOLDED
-	/* Setup fixmap PMD */
+	/* Setup fixmap PUD and PMD */
+	if (pgtable_l4_enabled)
+		create_pud_mapping(fixmap_pud, FIXADDR_START,
+				   (uintptr_t)fixmap_pmd, PUD_SIZE, PAGE_TABLE);
 	create_pmd_mapping(fixmap_pmd, FIXADDR_START,
 			   (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
 	/* Setup trampoline PGD and PMD */
 	create_pgd_mapping(trampoline_pg_dir, kernel_map.virt_addr,
-			   (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
+			   trampoline_pgd_next, PGDIR_SIZE, PAGE_TABLE);
+	if (pgtable_l4_enabled)
+		create_pud_mapping(trampoline_pud, kernel_map.virt_addr,
+				   (uintptr_t)trampoline_pmd, PUD_SIZE, PAGE_TABLE);
 #ifdef CONFIG_XIP_KERNEL
 	create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr,
 			   kernel_map.xiprom, PMD_SIZE, PAGE_KERNEL_EXEC);
@@ -711,7 +874,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	 * Bootime fixmap only can handle PMD_SIZE mapping. Thus, boot-ioremap
 	 * range can not span multiple pmds.
 	 */
-	BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
+	BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 		     != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
 
 #ifndef __PAGETABLE_PMD_FOLDED
@@ -782,9 +945,10 @@ static void __init setup_vm_final(void)
 	/* Clear fixmap PTE and PMD mappings */
 	clear_fixmap(FIX_PTE);
 	clear_fixmap(FIX_PMD);
+	clear_fixmap(FIX_PUD);
 
 	/* Move to swapper page table */
-	csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
+	csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | satp_mode);
 	local_flush_tlb_all();
 
 	pt_ops_set_late();