forked from xamidev/pepperOS
111 lines
3.1 KiB
C
111 lines
3.1 KiB
C
/*
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* @author xamidev <xamidev@riseup.net>
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* @brief Physical memory manager from freelist
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* @license GPL-3.0-only
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*/
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/*
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pmm - Physical Memory Manager
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will manage 4kb pages physically
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it will probably need to get some info from Limine,
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to see which pages are used by kernel/bootloader/mmio/fb etc.
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*/
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#include "paging.h"
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#include <limine.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <kernel.h>
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#include "mem/misc/utils.h"
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#include "pmm.h"
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/*
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First we'll have to discover the physical memory layout,
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and for that we can use a Limine request.
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*/
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/*
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We will look for the biggest usable physical memory region
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and use this for the bitmap. The reserved memory will be ignored.
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*/
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struct limine_memmap_entry* biggest_entry;
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static void pmm_find_biggest_usable_region(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
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{
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// Max length of a usable memory region
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uint64_t length_max = 0;
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uint64_t offset = hhdm->offset;
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DEBUG("Usable Memory:");
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for (size_t i=0; i<memmap->entry_count; i++)
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{
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struct limine_memmap_entry* entry = memmap->entries[i];
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if (entry->type == LIMINE_MEMMAP_USABLE)
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{
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DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", entry->base, entry->base+entry->length,
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entry->base+offset, entry->base+entry->length+offset);
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if (entry->length > length_max)
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{
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length_max = entry->length;
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biggest_entry = entry;
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}
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}
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}
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DEBUG("Biggest usable memory region:");
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DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", biggest_entry->base, biggest_entry->base + biggest_entry->length,
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biggest_entry->base+offset, biggest_entry->base+biggest_entry->length+offset);
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}
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// Offset from Higher Half Direct Map
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uint64_t hhdm_off;
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static uintptr_t g_freelist = 0;
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uintptr_t pmm_alloc()
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{
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if (!g_freelist)
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{
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panic(NULL, "PMM is out of memory!");
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}
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uintptr_t addr = g_freelist;
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g_freelist = *(uintptr_t*) PHYS_TO_VIRT(g_freelist);
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return addr;
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}
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void pmm_free(uintptr_t addr)
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{
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*(uintptr_t*) PHYS_TO_VIRT(addr) = g_freelist;
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g_freelist = addr;
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}
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static void pmm_init_freelist()
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{
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// We simply call pmm_free() on each page that is marked USABLE
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// in our big memory region.
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uint64_t base = ALIGN_UP(biggest_entry->base, PAGE_SIZE);
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uint64_t end = ALIGN_DOWN(biggest_entry->base + biggest_entry->length, PAGE_SIZE);
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uint64_t page_count=0;
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for (uint64_t addr = base; addr < end; addr += PAGE_SIZE)
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{
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pmm_free(addr);
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//DEBUG("page %u lives at phys 0x%p (virt 0x%p)", page_count, addr, PHYS_TO_VIRT(addr));
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page_count++;
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}
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DEBUG("%u frames in freelist, available for use (%u bytes)", page_count, page_count*PAGE_SIZE);
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}
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void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
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{
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hhdm_off = hhdm->offset;
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pmm_find_biggest_usable_region(memmap, hhdm);
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//pmm_allocate_bitmap(hhdm); too complicated for my small brain
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// Now we have biggest USABLE region,
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// so to populate the free list we just iterate through it
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pmm_init_freelist();
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}
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