[PATCH 1/3] riscv/mm: Add pkmap region and CONFIG_HIGHMEM

Eric Lin
2020-03-31T09:49:55Z

To support kmap(), we add pkmap region and move origin memory
layout which including fixmap, pci_io, vmemmap and vmalloc region
after PAGE_OFFSET to leave user more space. And we reserve 4MB
from TOP of RAM to make sure each region before it can align with
PGDIR_SIZE.

max_low_pfn is the end of lowmem and the start of highmem.
In setup_vm_final() we just setup page table to the end of lowmem,
and after lowmem, each memory region will maintain its page table.

We must set memblock_set_current_limit() to max_low_pfn, because in
memblock_phys_alloc(), it will allocate memory default from top of
physical RAM which will use highmem zone pages that doesn't create
page table mappings.

Signed-off-by: Eric Lin <tesheng@andestech.com>
Cc: Alan Kao <alankao@andestech.com>
---
arch/riscv/Kconfig | 18 +++++++
arch/riscv/include/asm/highmem.h | 19 ++++++++
arch/riscv/include/asm/pgtable.h | 22 +++++++++
arch/riscv/mm/init.c | 84 ++++++++++++++++++++++++++++++--
4 files changed, 140 insertions(+), 3 deletions(-)
create mode 100644 arch/riscv/include/asm/highmem.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index cd5db57bfd41..079443cbe382 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -288,6 +288,24 @@ config FPU

If you don't know what to do here, say Y.

+config HIGHMEM
+ bool "High Memory Support"
+ depends on 32BIT && MMU
+ default n
+ help
+ The address space of RV32 processors is only 4 Gigabytes large
+ and it has to accommodate user address space, kernel address
+ space as well as some memory mapped IO. That means that, if you
+ have a large amount of physical memory and/or IO, not all of the
+ memory can be "permanently mapped" by the kernel. The physical
+ memory that is not permanently mapped is called "high memory".
+
+ Depending on the selected kernel/user memory split, minimum
+ vmalloc space and actual amount of RAM, you may not need this
+ option which should result in a slightly faster kernel.
+
+ If unsure, say n.
+
endmenu

menu "Kernel features"
diff --git a/arch/riscv/include/asm/highmem.h b/arch/riscv/include/asm/highmem.h
new file mode 100644
index 000000000000..7fc79e58f607
--- /dev/null
+++ b/arch/riscv/include/asm/highmem.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Andes Technology Corporation
+ */
+
+#ifndef _ASM_HIGHMEM_H
+#define _ASM_HIGHMEM_H
+
+#include <asm/kmap_types.h>
+#include <asm/cacheflush.h>
+#include <asm/pgtable.h>
+#include <asm/fixmap.h>
+
+#define PKMAP_BASE (FIXADDR_START - SZ_2M)
+#define LAST_PKMAP (SZ_2M >> PAGE_SHIFT)
+#define LAST_PKMAP_MASK (LAST_PKMAP - 1)
+#define PKMAP_NR(virt) (((virt) - (PKMAP_BASE)) >> PAGE_SHIFT)
+#define PKMAP_ADDR(nr) (PKMAP_BASE + ((nr) << PAGE_SHIFT))
+#define kmap_prot PAGE_KERNEL
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 393f2014dfee..d9a3769f1f4e 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -21,6 +21,16 @@

#ifdef CONFIG_MMU

+#ifdef CONFIG_HIGHMEM
+#define VMALLOC_SIZE (SZ_128M)
+/* Reserve 4MB from top of RAM to align with PGDIR_SIZE */
+#define VMALLOC_END (0xffc00000UL)
+#define VMALLOC_START (VMALLOC_END - VMALLOC_SIZE)
+
+#define BPF_JIT_REGION_SIZE (VMALLOC_SIZE >> 2)
+#define BPF_JIT_REGION_START (VMALLOC_END - BPF_JIT_REGION_SIZE)
+#define BPF_JIT_REGION_END (VMALLOC_END)
+#else
#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
#define VMALLOC_END (PAGE_OFFSET - 1)
#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
@@ -28,6 +38,7 @@
#define BPF_JIT_REGION_SIZE (SZ_128M)
#define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE)
#define BPF_JIT_REGION_END (VMALLOC_END)
+#endif /* CONFIG_HIGHMEM */

/*
* Roughly size the vmemmap space to be large enough to fit enough
@@ -60,6 +71,12 @@

#endif

+#ifdef CONFIG_HIGHMEM
+/* Set LOWMEM_END alignment with PGDIR_SIZE */
+#define LOWMEM_END (ALIGN_DOWN(PKMAP_BASE, SZ_4M))
+#define LOWMEM_SIZE (LOWMEM_END - PAGE_OFFSET)
+#endif /* CONFIG_HIGHMEM */
+
#ifdef CONFIG_64BIT
#include <asm/pgtable-64.h>
#else
@@ -455,8 +472,13 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
#ifdef CONFIG_64BIT
#define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)
#else
+#ifdef CONFIG_HIGHMEM
+#define TASK_SIZE PAGE_OFFSET
+#else
+#include<asm/fixmap.h>
#define TASK_SIZE FIXADDR_START
#endif
+#endif

#else /* CONFIG_MMU */

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index fab855963c73..59afb479176a 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -37,7 +37,9 @@ static void __init zone_sizes_init(void)
(unsigned long) PFN_PHYS(max_low_pfn)));
#endif
max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
-
+#ifdef CONFIG_HIGHMEM
+ max_zone_pfns[ZONE_HIGHMEM] = max_pfn;
+#endif
free_area_init_nodes(max_zone_pfns);
}

@@ -46,6 +48,22 @@ static void setup_zero_page(void)
memset((void *)empty_zero_page, 0, PAGE_SIZE);
}

+#ifdef CONFIG_HIGHMEM
+static inline void __init free_highmem(void)
+{
+ unsigned long pfn;
+
+ for (pfn = PFN_UP(__pa(high_memory)); pfn < max_pfn; pfn++) {
+ phys_addr_t paddr = (phys_addr_t)pfn << PAGE_SHIFT;
+
+ if (!memblock_is_reserved(paddr))
+ free_highmem_page(pfn_to_page(pfn));
+ }
+}
+#else
+static inline void __init free_highmem(void) { }
+#endif
+
#ifdef CONFIG_DEBUG_VM
static inline void print_mlk(char *name, unsigned long b, unsigned long t)
{
@@ -85,6 +103,7 @@ void __init mem_init(void)

high_memory = (void *)(__va(PFN_PHYS(max_low_pfn)));
memblock_free_all();
+ free_highmem();

mem_init_print_info(NULL);
print_vm_layout();
@@ -132,7 +151,16 @@ void __init setup_bootmem(void)
phys_addr_t end = reg->base + reg->size;

if (reg->base <= vmlinux_start && vmlinux_end <= end) {
+#ifdef CONFIG_HIGHMEM
+ /*
+ * In RV32, physical RAM might be large than 1GB,
+ * so we just set reg->size as mem_size.
+ */
+ mem_size = reg->size;
+#else
mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
+#endif
+

/*
* Remove memblock from the end of usable area to the
@@ -149,8 +177,13 @@ void __init setup_bootmem(void)
memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);

set_max_mapnr(PFN_DOWN(mem_size));
+#ifdef CONFIG_HIGHMEM
+ max_low_pfn = (PFN_DOWN(__pa(LOWMEM_END)));
+ max_pfn = PFN_DOWN(memblock_end_of_DRAM());
+ memblock_set_current_limit(__pa(LOWMEM_END));
+#else
max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
-
+#endif
#ifdef CONFIG_BLK_DEV_INITRD
setup_initrd();
#endif /* CONFIG_BLK_DEV_INITRD */
@@ -451,8 +484,16 @@ static void __init setup_vm_final(void)
/* Map all memory banks */
for_each_memblock(memory, reg) {
start = reg->base;
+#ifdef CONFIG_HIGHMEM
+ /*
+ * If enable HIGHMEM, we only setup page table
+ * to the end of lowmem.
+ */
+ BUG_ON((LOWMEM_SIZE % PGDIR_SIZE) != 0);
+ end = start + LOWMEM_SIZE;
+#else
end = start + reg->size;
-
+#endif
if (start >= end)
break;
if (memblock_is_nomap(reg))
@@ -488,6 +529,42 @@ static inline void setup_vm_final(void)
}
#endif /* CONFIG_MMU */

+#ifdef CONFIG_HIGHMEM
+static void __init pkmap_init(void)
+{
+ unsigned long vaddr;
+ unsigned long pfn;
+ pgd_t *pgd;
+ p4d_t *p4d;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pkmap_p;
+
+ /*
+ * Permanent kmaps:
+ */
+ vaddr = PKMAP_BASE;
+
+ pgd = swapper_pg_dir + pgd_index(vaddr);
+ p4d = p4d_offset(pgd, vaddr);
+ pud = pud_offset(p4d, vaddr);
+ pmd = pmd_offset(pud, vaddr);
+ pkmap_p = (pte_t *)__va(memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE));
+ if (!pkmap_p)
+ panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
+ __func__, PAGE_SIZE, PAGE_SIZE);
+ memset(pkmap_p, 0, PAGE_SIZE);
+ pfn = PFN_DOWN(__pa(pkmap_p));
+ set_pmd(pmd, __pmd((pfn << _PAGE_PFN_SHIFT) |
+ pgprot_val(__pgprot(_PAGE_TABLE))));
+
+ /* Adjust pkmap page table base */
+ pkmap_page_table = pkmap_p + pte_index(vaddr);
+}
+#else
+static void __init pkmap_init(void){ }
+#endif
+
void __init paging_init(void)
{
setup_vm_final();
@@ -495,6 +572,7 @@ void __init paging_init(void)
sparse_init();
setup_zero_page();
zone_sizes_init();
+ pkmap_init();
}

#ifdef CONFIG_SPARSEMEM_VMEMMAP
--
2.17.0