[PATCH v4 0/2] Two-stagged initial page table setup

[PATCH v4 0/2] Two-stagged initial page table setup

[Anup Patel]

This patchset implements two-stagged initial page table setup using fixmap
to avoid mapping non-existent RAM and also reduce high_memory consumed by
initial page tables.

The patchset is based on Linux-5.1-rc7 and tested on SiFive Unleashed board
and QEMU virt machine.

These patches can be found in riscv_setup_vm_v4 branch of
https//github.com/avpatel/linux.git

Changes since v3:
- Changed patch series subject.
- Dropped PATCH1 because it's already merged
- Dropped PATCH3 because trampoline page table handles a corner case
  for 32bit systems where load address range overlaps kernel virtual
  address range
- Revamped PATCH for 4K aligned booting into two-stagged initial page
  table setup

Changes since v2:
- Dropped PATCH2 because we have separate fix for Linux-5.1-rcX
- Moved PATCH5 to PATCH2
- Moved PATCH4 to PATCH3
- The "Booting kernel from any 4KB aligned address" is now PATCH4

Changes since v1:
- Add kconfig option BOOT_PAGE_ALIGNED to enable 4KB aligned booting
- Improved initial page table setup code to select best/biggest
  possible mapping size based on load address alignment
- Added PATCH4 to remove redundant trampoline page table
- Added PATCH5 to fix memory reservation in setup_bootmem()

Anup Patel (2):
  RISC-V: Fix memory reservation in setup_bootmem()
  RISC-V: Setup initial page tables in two stages

 arch/riscv/include/asm/fixmap.h     |   5 +
 arch/riscv/include/asm/pgtable-64.h |   5 +
 arch/riscv/include/asm/pgtable.h    |   7 +
 arch/riscv/kernel/head.S            |  17 +-
 arch/riscv/kernel/setup.c           |   4 +-
 arch/riscv/mm/init.c                | 327 ++++++++++++++++++++++------
 6 files changed, 289 insertions(+), 76 deletions(-)

--
2.17.1
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[PATCH v4 1/2] RISC-V: Fix memory reservation in setup_bootmem()

[Anup Patel]

Currently, the setup_bootmem() reserves memory from RAM start to the
kernel end. This prevents us from exploring ways to use the RAM below
(or before) the kernel start hence this patch updates setup_bootmem()
to only reserve memory from the kernel start to the kernel end.

Suggested-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 arch/riscv/mm/init.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index bc7b77e34d09..ab175b655933 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -29,6 +29,8 @@ unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
 							__page_aligned_bss;
 EXPORT_SYMBOL(empty_zero_page);
 
+extern char _start[];
+
 static void __init zone_sizes_init(void)
 {
 	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
@@ -108,18 +110,14 @@ void __init setup_bootmem(void)
 {
 	struct memblock_region *reg;
 	phys_addr_t mem_size = 0;
+	phys_addr_t vmlinux_end = __pa(&_end);
+	phys_addr_t vmlinux_start = __pa(&_start);
 
 	/* Find the memory region containing the kernel */
 	for_each_memblock(memory, reg) {
-		phys_addr_t vmlinux_end = __pa(_end);
 		phys_addr_t end = reg->base + reg->size;
 
 		if (reg->base <= vmlinux_end && vmlinux_end <= end) {
-			/*
-			 * Reserve from the start of the region to the end of
-			 * the kernel
-			 */
-			memblock_reserve(reg->base, vmlinux_end - reg->base);
 			mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
 
 			/*
@@ -133,6 +131,9 @@ void __init setup_bootmem(void)
 	}
 	BUG_ON(mem_size == 0);
 
+	/* Reserve from the start of the kernel to the end of the kernel */
+	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
+
 	set_max_mapnr(PFN_DOWN(mem_size));
 	max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
 
@@ -210,7 +211,6 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 
 asmlinkage void __init setup_vm(void)
 {
-	extern char _start;
 	uintptr_t i;
 	uintptr_t pa = (uintptr_t) &_start;
 	pgprot_t prot = __pgprot(pgprot_val(PAGE_KERNEL) | _PAGE_EXEC);
-- 
2.17.1

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[PATCH v4 2/2] RISC-V: Setup initial page tables in two stages

[Anup Patel]

Currently, the setup_vm() does initial page table setup in one-shot
very early before enabling MMU. Due to this, the setup_vm() has to map
all possible kernel virtual addresses since it does not know size and
location of RAM. This means we have kernel mappings for non-existent
RAM and any buggy driver (or kernel) code doing out-of-bound access
to RAM will not fault and cause underterministic behaviour.

Further, the setup_vm() creates PMD mappings (i.e. 2M mappings) for
RV64 systems. This means for PAGE_OFFSET=0xffffffe000000000 (i.e.
MAXPHYSMEM_128GB=y), the setup_vm() will require 129 pages (i.e.
516 KB) of memory for initial page tables which is never freed. The
memory required for initial page tables will further increase if
we chose a lower value of PAGE_OFFSET (e.g. 0xffffff0000000000)

This patch implements two-staged initial page table setup, as follows:
1. Early (i.e. setup_vm()): This stage maps kernel image and DTB in
a early page table (i.e. early_pg_dir). The early_pg_dir will be used
only by boot HART so it can be freed as-part of init memory free-up.
2. Final (i.e. setup_vm_final()): This stage maps all possible RAM
banks in the final page table (i.e. swapper_pg_dir). The boot HART
will start using swapper_pg_dir at the end of setup_vm_final(). All
non-boot HARTs directly use the swapper_pg_dir created by boot HART.

We have following advantages with this new approach:
1. Kernel mappings for non-existent RAM don't exists anymore.
2. Memory consumed by initial page tables is now indpendent of the
chosen PAGE_OFFSET.
3. Memory consumed by initial page tables on RV64 system is 2 pages
(i.e. 8 KB) which has significantly reduced and these pages will be
freed as-part of the init memory free-up.

The patch also provides a foundation for implementing strict kernel
mappings where we protect kernel text and rodata using PTE permissions.

Suggested-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
---
 arch/riscv/include/asm/fixmap.h     |   5 +
 arch/riscv/include/asm/pgtable-64.h |   5 +
 arch/riscv/include/asm/pgtable.h    |   7 +
 arch/riscv/kernel/head.S            |  17 +-
 arch/riscv/kernel/setup.c           |   4 +-
 arch/riscv/mm/init.c                | 313 ++++++++++++++++++++++------
 6 files changed, 282 insertions(+), 69 deletions(-)

diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
index c207f6634b91..9c66033c3a54 100644
--- a/arch/riscv/include/asm/fixmap.h
+++ b/arch/riscv/include/asm/fixmap.h
@@ -21,6 +21,11 @@
  */
 enum fixed_addresses {
 	FIX_HOLE,
+#define FIX_FDT_SIZE	SZ_1M
+	FIX_FDT_END,
+	FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
+	FIX_PTE,
+	FIX_PMD,
 	FIX_EARLYCON_MEM_BASE,
 	__end_of_fixed_addresses
 };
diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
index 7aa0ea9bd8bb..56ecc3dc939d 100644
--- a/arch/riscv/include/asm/pgtable-64.h
+++ b/arch/riscv/include/asm/pgtable-64.h
@@ -78,6 +78,11 @@ static inline pmd_t pfn_pmd(unsigned long pfn, pgprot_t prot)
 	return __pmd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
 }
 
+static inline unsigned long _pmd_pfn(pmd_t pmd)
+{
+	return pmd_val(pmd) >> _PAGE_PFN_SHIFT;
+}
+
 #define pmd_ERROR(e) \
 	pr_err("%s:%d: bad pmd %016lx.\n", __FILE__, __LINE__, pmd_val(e))
 
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 1141364d990e..3dfe7ba95acb 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -67,6 +67,8 @@
 #define PAGE_KERNEL		__pgprot(_PAGE_KERNEL)
 #define PAGE_KERNEL_EXEC	__pgprot(_PAGE_KERNEL | _PAGE_EXEC)
 
+#define PAGE_TABLE		__pgprot(_PAGE_TABLE)
+
 extern pgd_t swapper_pg_dir[];
 
 /* MAP_PRIVATE permissions: xwr (copy-on-write) */
@@ -127,6 +129,11 @@ static inline pgd_t pfn_pgd(unsigned long pfn, pgprot_t prot)
 	return __pgd((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
 }
 
+static inline unsigned long _pgd_pfn(pgd_t pgd)
+{
+	return pgd_val(pgd) >> _PAGE_PFN_SHIFT;
+}
+
 #define pgd_index(addr) (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
 
 /* Locate an entry in the page global directory */
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index fe884cd69abd..f94f89bc321f 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -62,7 +62,9 @@ clear_bss_done:
 
 	/* Initialize page tables and relocate to virtual addresses */
 	la sp, init_thread_union + THREAD_SIZE
+	mv a0, s1
 	call setup_vm
+	la a0, early_pg_dir
 	call relocate
 
 	/* Restore C environment */
@@ -82,18 +84,17 @@ clear_bss_done:
 relocate:
 	/* Relocate return address */
 	li a1, PAGE_OFFSET
-	la a0, _start
-	sub a1, a1, a0
+	la a2, _start
+	sub a1, a1, a2
 	add ra, ra, a1
 
 	/* Point stvec to virtual address of intruction after satp write */
-	la a0, 1f
-	add a0, a0, a1
-	csrw stvec, a0
+	la a2, 1f
+	add a2, a2, a1
+	csrw stvec, a2
 
 	/* Compute satp for kernel page tables, but don't load it yet */
-	la a2, swapper_pg_dir
-	srl a2, a2, PAGE_SHIFT
+	srl a2, a0, PAGE_SHIFT
 	li a1, SATP_MODE
 	or a2, a2, a1
 
@@ -120,6 +121,7 @@ relocate:
 
 	/* Switch to kernel page tables */
 	csrw sptbr, a2
+	sfence.vma
 
 	ret
 
@@ -151,6 +153,7 @@ relocate:
 	fence
 
 	/* Enable virtual memory and relocate to virtual address */
+	la a0, swapper_pg_dir
 	call relocate
 
 	tail smp_callin
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 540a331d1376..79670458527d 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -30,6 +30,7 @@
 #include <linux/sched/task.h>
 #include <linux/swiotlb.h>
 
+#include <asm/fixmap.h>
 #include <asm/setup.h>
 #include <asm/sections.h>
 #include <asm/pgtable.h>
@@ -54,7 +55,8 @@ unsigned long boot_cpu_hartid;
 
 void __init parse_dtb(unsigned int hartid, void *dtb)
 {
-	if (early_init_dt_scan(__va(dtb)))
+	dtb = (void *)fix_to_virt(FIX_FDT) + ((uintptr_t)dtb & ~PAGE_MASK);
+	if (early_init_dt_scan(dtb))
 		return;
 
 	pr_err("No DTB passed to the kernel\n");
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index ab175b655933..4220743c49c5 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1,14 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * 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.
+ * Copyright (C) 2019 Western Digital Corporation or its affiliates.
  */
 
 #include <linux/init.h>
@@ -49,13 +42,6 @@ void setup_zero_page(void)
 	memset((void *)empty_zero_page, 0, PAGE_SIZE);
 }
 
-void __init paging_init(void)
-{
-	setup_zero_page();
-	local_flush_tlb_all();
-	zone_sizes_init();
-}
-
 void __init mem_init(void)
 {
 #ifdef CONFIG_FLATMEM
@@ -162,16 +148,13 @@ unsigned long pfn_base;
 EXPORT_SYMBOL(pfn_base);
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
-pgd_t trampoline_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
+pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
+pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
+static bool mmu_enabled;
 
-#ifndef __PAGETABLE_PMD_FOLDED
-#define NUM_SWAPPER_PMDS ((uintptr_t)-PAGE_OFFSET >> PGDIR_SHIFT)
-pmd_t swapper_pmd[PTRS_PER_PMD*((-PAGE_OFFSET)/PGDIR_SIZE)] __page_aligned_bss;
-pmd_t trampoline_pmd[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
-pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
-#endif
+#define MAX_EARLY_MAPPING_SIZE	SZ_128M
 
-pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
+pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
 
 void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 {
@@ -190,6 +173,156 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 	}
 }
 
+static pte_t *__init get_pte_virt(phys_addr_t pa)
+{
+	if (mmu_enabled) {
+		clear_fixmap(FIX_PTE);
+		return (pte_t *)set_fixmap_offset(FIX_PTE, pa);
+	} else {
+		return (pte_t *)((uintptr_t)pa);
+	}
+}
+
+static phys_addr_t __init alloc_pte(uintptr_t va)
+{
+	/*
+	 * We only create PMD or PGD early mappings so we
+	 * should never reach here with MMU disabled.
+	 */
+	BUG_ON(!mmu_enabled);
+
+	return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
+}
+
+static void __init create_pte_mapping(pte_t *ptep,
+				      uintptr_t va, phys_addr_t pa,
+				      phys_addr_t sz, pgprot_t prot)
+{
+	uintptr_t pte_index = pte_index(va);
+
+	BUG_ON(sz != PAGE_SIZE);
+
+	if (pte_none(ptep[pte_index]))
+		ptep[pte_index] = pfn_pte(PFN_DOWN(pa), prot);
+}
+
+#ifndef __PAGETABLE_PMD_FOLDED
+
+pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
+pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
+
+#if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE
+#define NUM_EARLY_PMDS		1UL
+#else
+#define NUM_EARLY_PMDS		(1UL + MAX_EARLY_MAPPING_SIZE / PGDIR_SIZE)
+#endif
+pmd_t early_pmd[PTRS_PER_PMD*NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
+
+static pmd_t *__init get_pmd_virt(phys_addr_t pa)
+{
+	if (mmu_enabled) {
+		clear_fixmap(FIX_PMD);
+		return (pmd_t *)set_fixmap_offset(FIX_PMD, pa);
+	} else {
+		return (pmd_t *)((uintptr_t)pa);
+	}
+}
+
+static phys_addr_t __init alloc_pmd(uintptr_t va)
+{
+	uintptr_t pmd_num;
+
+	if (mmu_enabled)
+		return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
+
+	pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
+	BUG_ON(pmd_num >= NUM_EARLY_PMDS);
+	return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
+}
+
+static void __init create_pmd_mapping(pmd_t *pmdp,
+				      uintptr_t va, phys_addr_t pa,
+				      phys_addr_t sz, pgprot_t prot)
+{
+	pte_t *ptep;
+	phys_addr_t pte_phys;
+	uintptr_t pmd_index = pmd_index(va);
+
+	if (sz == PMD_SIZE) {
+		if (pmd_none(pmdp[pmd_index]))
+			pmdp[pmd_index] = pfn_pmd(PFN_DOWN(pa), prot);
+		return;
+	}
+
+	if (pmd_none(pmdp[pmd_index])) {
+		pte_phys = alloc_pte(va);
+		pmdp[pmd_index] = pfn_pmd(PFN_DOWN(pte_phys), PAGE_TABLE);
+		ptep = get_pte_virt(pte_phys);
+		memset(ptep, 0, PAGE_SIZE);
+	} else {
+		pte_phys = PFN_PHYS(_pmd_pfn(pmdp[pmd_index]));
+		ptep = get_pte_virt(pte_phys);
+	}
+
+	create_pte_mapping(ptep, va, pa, sz, prot);
+}
+
+#define pgd_next_t		pmd_t
+#define alloc_pgd_next(__va)	alloc_pmd(__va)
+#define get_pgd_next_virt(__pa)	get_pmd_virt(__pa)
+#define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)	\
+	create_pmd_mapping(__nextp, __va, __pa, __sz, __prot)
+#define PTE_PARENT_SIZE		PMD_SIZE
+#define fixmap_pgd_next		fixmap_pmd
+#else
+#define pgd_next_t		pte_t
+#define alloc_pgd_next(__va)	alloc_pte(__va)
+#define get_pgd_next_virt(__pa)	get_pte_virt(__pa)
+#define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)	\
+	create_pte_mapping(__nextp, __va, __pa, __sz, __prot)
+#define PTE_PARENT_SIZE		PGDIR_SIZE
+#define fixmap_pgd_next		fixmap_pte
+#endif
+
+static void __init create_pgd_mapping(pgd_t *pgdp,
+				      uintptr_t va, phys_addr_t pa,
+				      phys_addr_t sz, pgprot_t prot)
+{
+	pgd_next_t *nextp;
+	phys_addr_t next_phys;
+	uintptr_t pgd_index = pgd_index(va);
+
+	if (sz == PGDIR_SIZE) {
+		if (pgd_val(pgdp[pgd_index]) == 0)
+			pgdp[pgd_index] = pfn_pgd(PFN_DOWN(pa), prot);
+		return;
+	}
+
+	if (pgd_val(pgdp[pgd_index]) == 0) {
+		next_phys = alloc_pgd_next(va);
+		pgdp[pgd_index] = pfn_pgd(PFN_DOWN(next_phys), PAGE_TABLE);
+		nextp = get_pgd_next_virt(next_phys);
+		memset(nextp, 0, PAGE_SIZE);
+	} else {
+		next_phys = PFN_PHYS(_pgd_pfn(pgdp[pgd_index]));
+		nextp = get_pgd_next_virt(next_phys);
+	}
+
+	create_pgd_next_mapping(nextp, va, pa, sz, prot);
+}
+
+static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
+{
+	uintptr_t map_size = PAGE_SIZE;
+
+	/* Upgrade to PMD/PGDIR mappings whenever possible */
+	if (!(base & (PTE_PARENT_SIZE - 1)) &&
+	    !(size & (PTE_PARENT_SIZE - 1)))
+		map_size = PTE_PARENT_SIZE;
+
+	return map_size;
+}
+
 /*
  * setup_vm() is called from head.S with MMU-off.
  *
@@ -209,54 +342,112 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 	"not use absolute addressing."
 #endif
 
-asmlinkage void __init setup_vm(void)
+asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
-	uintptr_t i;
-	uintptr_t pa = (uintptr_t) &_start;
-	pgprot_t prot = __pgprot(pgprot_val(PAGE_KERNEL) | _PAGE_EXEC);
+	uintptr_t va, end_va;
+	uintptr_t load_pa = (uintptr_t)(&_start);
+	uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
+	uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
+
+	va_pa_offset = PAGE_OFFSET - load_pa;
+	pfn_base = PFN_DOWN(load_pa);
 
-	va_pa_offset = PAGE_OFFSET - pa;
-	pfn_base = PFN_DOWN(pa);
+	/*
+	 * Enforce boot alignment requirements of RV32 and
+	 * RV64 by only allowing PMD or PGD mappings.
+	 */
+	BUG_ON(map_size == PAGE_SIZE);
 
 	/* Sanity check alignment and size */
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
-	BUG_ON((pa % (PAGE_SIZE * PTRS_PER_PTE)) != 0);
+	BUG_ON((load_pa % map_size) != 0);
+	BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
+
+	/* Setup early PGD for fixmap */
+	create_pgd_mapping(early_pg_dir, FIXADDR_START,
+			   (uintptr_t)fixmap_pgd_next, PGDIR_SIZE, PAGE_TABLE);
 
 #ifndef __PAGETABLE_PMD_FOLDED
-	trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)trampoline_pmd),
-			__pgprot(_PAGE_TABLE));
-	trampoline_pmd[0] = pfn_pmd(PFN_DOWN(pa), prot);
+	/* Setup fixmap PMD */
+	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, PAGE_OFFSET,
+			   (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
+	create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
+			   load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
+#else
+	/* Setup trampoline PGD */
+	create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
+			   load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
+#endif
 
-	for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
-		size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
+	/*
+	 * Setup early PGD covering entire kernel which will allows
+	 * us to reach paging_init(). We map all memory banks later
+	 * in setup_vm_final() below.
+	 */
+	end_va = PAGE_OFFSET + load_sz;
+	for (va = PAGE_OFFSET; va < end_va; va += map_size)
+		create_pgd_mapping(early_pg_dir, va,
+				   load_pa + (va - PAGE_OFFSET),
+				   map_size, PAGE_KERNEL_EXEC);
+
+	/* Create fixed mapping for early FDT parsing */
+	end_va = __fix_to_virt(FIX_FDT) + FIX_FDT_SIZE;
+	for (va = __fix_to_virt(FIX_FDT); va < end_va; va += PAGE_SIZE)
+		create_pte_mapping(fixmap_pte, va,
+				   dtb_pa + (va - __fix_to_virt(FIX_FDT)),
+				   PAGE_SIZE, PAGE_KERNEL);
+}
 
-		swapper_pg_dir[o] =
-			pfn_pgd(PFN_DOWN((uintptr_t)swapper_pmd) + i,
-				__pgprot(_PAGE_TABLE));
-	}
-	for (i = 0; i < ARRAY_SIZE(swapper_pmd); i++)
-		swapper_pmd[i] = pfn_pmd(PFN_DOWN(pa + i * PMD_SIZE), prot);
-
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pmd),
-				__pgprot(_PAGE_TABLE));
-	fixmap_pmd[(FIXADDR_START >> PMD_SHIFT) % PTRS_PER_PMD] =
-		pfn_pmd(PFN_DOWN((uintptr_t)fixmap_pte),
-				__pgprot(_PAGE_TABLE));
-#else
-	trampoline_pg_dir[(PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN(pa), prot);
+static void __init setup_vm_final(void)
+{
+	uintptr_t va, map_size;
+	phys_addr_t pa, start, end;
+	struct memblock_region *reg;
+
+	/* Set mmu_enabled flag */
+	mmu_enabled = true;
 
-	for (i = 0; i < (-PAGE_OFFSET)/PGDIR_SIZE; ++i) {
-		size_t o = (PAGE_OFFSET >> PGDIR_SHIFT) % PTRS_PER_PGD + i;
+	/* Setup swapper PGD for fixmap */
+	create_pgd_mapping(swapper_pg_dir, FIXADDR_START,
+			   __pa(fixmap_pgd_next),
+			   PGDIR_SIZE, PAGE_TABLE);
 
-		swapper_pg_dir[o] =
-			pfn_pgd(PFN_DOWN(pa + i * PGDIR_SIZE), prot);
+	/* Map all memory banks */
+	for_each_memblock(memory, reg) {
+		start = reg->base;
+		end = start + reg->size;
+
+		if (start >= end)
+			break;
+		if (memblock_is_nomap(reg))
+			continue;
+		if (start <= __pa(PAGE_OFFSET) &&
+		    __pa(PAGE_OFFSET) < end)
+			start = __pa(PAGE_OFFSET);
+
+		map_size = best_map_size(start, end - start);
+		for (pa = start; pa < end; pa += map_size) {
+			va = (uintptr_t)__va(pa);
+			create_pgd_mapping(swapper_pg_dir, va, pa,
+					   map_size, PAGE_KERNEL_EXEC);
+		}
 	}
 
-	swapper_pg_dir[(FIXADDR_START >> PGDIR_SHIFT) % PTRS_PER_PGD] =
-		pfn_pgd(PFN_DOWN((uintptr_t)fixmap_pte),
-				__pgprot(_PAGE_TABLE));
-#endif
+	/* Clear fixmap PTE and PMD mappings */
+	clear_fixmap(FIX_PTE);
+	clear_fixmap(FIX_PMD);
+
+	/* Move to swapper page table */
+	csr_write(sptbr, PFN_DOWN(__pa(swapper_pg_dir)) | SATP_MODE);
+	local_flush_tlb_all();
+}
+
+void __init paging_init(void)
+{
+	setup_vm_final();
+	setup_zero_page();
+	zone_sizes_init();
 }
-- 
2.17.1

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Re: [PATCH v4 0/2] Two-stagged initial page table setup

[Anup Patel]

On Thu, May 2, 2019 at 10:32 AM Anup Patel <Anup.Patel@wdc.com> wrote:
>
> This patchset implements two-stagged initial page table setup using fixmap
> to avoid mapping non-existent RAM and also reduce high_memory consumed by
> initial page tables.
>
> The patchset is based on Linux-5.1-rc7 and tested on SiFive Unleashed board
> and QEMU virt machine.
>
> These patches can be found in riscv_setup_vm_v4 branch of
> https//github.com/avpatel/linux.git
>
> Changes since v3:
> - Changed patch series subject.
> - Dropped PATCH1 because it's already merged
> - Dropped PATCH3 because trampoline page table handles a corner case
>   for 32bit systems where load address range overlaps kernel virtual
>   address range
> - Revamped PATCH for 4K aligned booting into two-stagged initial page
>   table setup
>
> Changes since v2:
> - Dropped PATCH2 because we have separate fix for Linux-5.1-rcX
> - Moved PATCH5 to PATCH2
> - Moved PATCH4 to PATCH3
> - The "Booting kernel from any 4KB aligned address" is now PATCH4
>
> Changes since v1:
> - Add kconfig option BOOT_PAGE_ALIGNED to enable 4KB aligned booting
> - Improved initial page table setup code to select best/biggest
>   possible mapping size based on load address alignment
> - Added PATCH4 to remove redundant trampoline page table
> - Added PATCH5 to fix memory reservation in setup_bootmem()
>
> Anup Patel (2):
>   RISC-V: Fix memory reservation in setup_bootmem()
>   RISC-V: Setup initial page tables in two stages
>
>  arch/riscv/include/asm/fixmap.h     |   5 +
>  arch/riscv/include/asm/pgtable-64.h |   5 +
>  arch/riscv/include/asm/pgtable.h    |   7 +
>  arch/riscv/kernel/head.S            |  17 +-
>  arch/riscv/kernel/setup.c           |   4 +-
>  arch/riscv/mm/init.c                | 327 ++++++++++++++++++++++------
>  6 files changed, 289 insertions(+), 76 deletions(-)
>
> --
> 2.17.1

Hi All,

Any comments on this patchset?

Regards,
Anup

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Re: [PATCH v4 2/2] RISC-V: Setup initial page tables in two stages

[Christoph Hellwig]

>  void __init parse_dtb(unsigned int hartid, void *dtb)
>  {
> -	if (early_init_dt_scan(__va(dtb)))
> +	dtb = (void *)fix_to_virt(FIX_FDT) + ((uintptr_t)dtb & ~PAGE_MASK);
> +	if (early_init_dt_scan(dtb))

FYI, parse_dtb in mainline now lost the hartid argument and takes a
phys_addr_t for the dtb address.

That being said I find the above way to magic.  So we take the fixmap
address and then only the offset from something passed as a pointer?
This just looks very weird.  The way FIX_FDT is defined to add to my
confusion, which might partially be due to not understanding fixmaps
very well.  But it seems like at very least we should set up an
actual kernel pointer for the dtb in setup_vm based on what that
gets passed and stop passing any arguments to parse_dtb to keep
that magic in one place.  And possibly add some comment.

> +#if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE

It seems MAX_EARLY_MAPPING_SIZE is defined to a fix constant,
why do we need these conditionals?

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Re: [PATCH v4 2/2] RISC-V: Setup initial page tables in two stages

[Anup Patel]

On Mon, May 20, 2019 at 5:13 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> >  void __init parse_dtb(unsigned int hartid, void *dtb)
> >  {
> > -     if (early_init_dt_scan(__va(dtb)))
> > +     dtb = (void *)fix_to_virt(FIX_FDT) + ((uintptr_t)dtb & ~PAGE_MASK);
> > +     if (early_init_dt_scan(dtb))
>
> FYI, parse_dtb in mainline now lost the hartid argument and takes a
> phys_addr_t for the dtb address.

Okay, this patch is based on 5.1 kernel. I guess I will have to rebase
it anyway.

>
> That being said I find the above way to magic.  So we take the fixmap
> address and then only the offset from something passed as a pointer?
> This just looks very weird.  The way FIX_FDT is defined to add to my
> confusion, which might partially be due to not understanding fixmaps
> very well.  But it seems like at very least we should set up an
> actual kernel pointer for the dtb in setup_vm based on what that
> gets passed and stop passing any arguments to parse_dtb to keep
> that magic in one place.  And possibly add some comment.

I agree with your suggestion. I will setup early_dtb_ptr in setup_vm()
and use it here.

FYI, the fixmap virtual address range is not covered by linear va-to-pa
translation (i.e. __va() and __pa() cannot be used). The mapping
granularity of fixmap is always PAGE_SIZE hence add offset to
fix_to_virt(FIX_FDT).

>
> > +#if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE
>
> It seems MAX_EARLY_MAPPING_SIZE is defined to a fix constant,
> why do we need these conditionals?

Sure, I will remove the conditional. It's totally redundant. I forgot to
remove it previously.

Regards,
Anup

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