145 lines
4.5 KiB
C
145 lines
4.5 KiB
C
#include "assert.H"
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#include "exceptions.H"
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#include "console.H"
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#include "paging_low.H"
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#include "page_table.H"
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PageTable * PageTable::current_page_table = NULL;
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unsigned int PageTable::paging_enabled = 0;
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ContFramePool * PageTable::kernel_mem_pool = NULL;
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ContFramePool * PageTable::process_mem_pool = NULL;
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unsigned long PageTable::shared_size = 0;
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void PageTable::init_paging(ContFramePool * _kernel_mem_pool,
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ContFramePool * _process_mem_pool,
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const unsigned long _shared_size)
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{
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kernel_mem_pool = _kernel_mem_pool;
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process_mem_pool = process_mem_pool;
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shared_size = _shared_size;
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Console::puts("\nInitialized Paging System\n");
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}
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PageTable::PageTable()
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{
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unsigned long * temp_page_directory = (unsigned long *) ((kernel_mem_pool->get_frames(1)) << 12); // Getting frame address to assign to page directory.
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unsigned long * page_table = (unsigned long *) ((kernel_mem_pool->get_frames(1)) << 12); // Get another frame for the page table.
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unsigned long tempaddr = 0; // Temporary address iterator.
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// We need to map the first 4MB.
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// This first for loop was here in case I needed to set the first 2mb as not present.
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for(unsigned int i = 0; i < 512; i++)
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{
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page_table[i] = tempaddr | 3; // set bits 0 and 1 to present and read/write respectively
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tempaddr += 4096; // 4096 = 4kb
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}
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for(unsigned int i = 512; i < 1024; i++)
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{
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page_table[i] = tempaddr | 3; // set bits 0 and 1 to present and read/write respectively
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tempaddr += 4096; // 4096 = 4kb
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}
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// Fill first entry of page directory.
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temp_page_directory[0] = (unsigned long)page_table;
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temp_page_directory[0] = temp_page_directory[0] | 3;
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for(unsigned int j = 1; j < 1024; j++)
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{
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temp_page_directory[j] = 0 | 2;
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}
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page_directory = temp_page_directory;
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current_page_table = this;
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Console::puts("\nConstructed Page Table object\n");
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}
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void PageTable::load()
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{
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write_cr3((unsigned long)page_directory);
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Console::puti((unsigned long)page_directory);
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current_page_table = this;
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Console::puts("\nLoaded page table\n");
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}
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void PageTable::enable_paging()
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{
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write_cr3((unsigned long)current_page_table->page_directory);
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write_cr0(read_cr0() | 0x80000000);
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paging_enabled = read_cr0();
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Console::puts("\nEnabled paging\n");
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}
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void PageTable::handle_fault(REGS * _r)
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{
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// Initializing some variables to make things easier.
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unsigned long * temp_pd = (unsigned long *) (current_page_table->page_directory);
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unsigned long * temp_pt = (unsigned long *) (*temp_pd);
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unsigned long pt_index = (read_cr2() >> 12) & 0x3FFFFF;
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unsigned long pd_index = read_cr2() >> 22;
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// If there isn't a page table present.
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if(!(temp_pd[pd_index] & 1))
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{
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Console::puts("\nPage Table not Present.\n");
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unsigned long * new_pt = (unsigned long *) (kernel_mem_pool->get_frames(1) << 12);
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// Set new page table entries as present.
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// Start at beginning address for the page table
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// this should be pd_index << 22.
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unsigned long temp_addr = pd_index << 22;
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for(unsigned int i = 0; i < 1024; i++)
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{
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new_pt[i] = temp_addr | 3;
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temp_addr += 4096;
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}
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// Add page table to page directory.
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temp_pd[pd_index] = (unsigned long) new_pt;
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temp_pd[pd_index] = temp_pd[pd_index] | 3;
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}
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/*
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// Why is this commented out?
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// Unfortunately, for whatever reason, any time I try to call
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// process_mem_pool->get_frames() the entire program crashes.
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// I've tried evaluating lines immediately afterwards, adding
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// for(;;);, the program ignores this and continues to crash.
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// Since I have no idea why this is happening, I can only assume
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// I did something wrong in cont_frame_pool or that this is just
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// an issue I didn't address properly somewhere and didn't see
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// addressed in the instructions. Regardless, I left what I believe
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// would be the implementation of handle_fault in the case that I
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// needed to allocate a frame in process_mem_pool in order to
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// allocate a page for a process commented out so I could at least
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// show that I knew how it would be implemented.
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if(read_cr2() >> 22 > 0)
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{
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if(((unsigned long *)temp_pd[pd_index])[pt_index] & 1)
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{
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Console::puts("\nPage not present.\n");
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unsigned long * new_page = (unsigned long *) (process_mem_pool->get_frames(1) << 12);
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// Set new page as page table entry.
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((unsigned long *)temp_pd[pd_index])[pt_index] = (unsigned long) new_page | 3;
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}
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}
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*/
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Console::puts("\nhandled page fault\n");
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}
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