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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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671f9a3e2e
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> [paul.walmsley@sifive.com: updated to apply; fixed a checkpatch warning] Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
50 lines
1.3 KiB
C
50 lines
1.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2019 Western Digital Corporation or its affiliates.
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*/
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#ifndef _ASM_RISCV_FIXMAP_H
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#define _ASM_RISCV_FIXMAP_H
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#include <linux/kernel.h>
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#include <linux/sizes.h>
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#include <asm/page.h>
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#include <asm/pgtable.h>
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/*
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* Here we define all the compile-time 'special' virtual addresses.
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* The point is to have a constant address at compile time, but to
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* set the physical address only in the boot process.
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*
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* These 'compile-time allocated' memory buffers are page-sized. Use
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* set_fixmap(idx,phys) to associate physical memory with fixmap indices.
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*/
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enum fixed_addresses {
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FIX_HOLE,
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#define FIX_FDT_SIZE SZ_1M
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FIX_FDT_END,
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FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
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FIX_PTE,
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FIX_PMD,
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FIX_EARLYCON_MEM_BASE,
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__end_of_fixed_addresses
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};
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#define FIXADDR_SIZE (__end_of_fixed_addresses * PAGE_SIZE)
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#define FIXADDR_TOP (VMALLOC_START)
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#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
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#define FIXMAP_PAGE_IO PAGE_KERNEL
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#define __early_set_fixmap __set_fixmap
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#define __late_set_fixmap __set_fixmap
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#define __late_clear_fixmap(idx) __set_fixmap((idx), 0, FIXMAP_PAGE_CLEAR)
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extern void __set_fixmap(enum fixed_addresses idx,
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phys_addr_t phys, pgprot_t prot);
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#include <asm-generic/fixmap.h>
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#endif /* _ASM_RISCV_FIXMAP_H */
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