apio
e5cf32c7b3
Some pages, such as framebuffer pages, are not physical memory frames reserved for the current process. Some, such as the framebuffer, may be shared between all processes. Yet, on exit() or on exec(), a process frees all frames mapped into its address spaces. And on fork(), it copies all data between frames. So how could we map framebuffers. Simple: we use one of the bits in page table entries which are available to the OS, and mark whether that page is owned by the current process. If it is owned, it will be: - Freed on address space destruction - Its data will be copied to a new page owned by the child process on fork() If it is not owned, it will be: - Left alone on address space destruction - On fork(), the child's virtual page will be mapped to the same physical frame as the parent This still needs a bit more work, such as keeping a reference of how many processes use a page to free it when all processes using it exit/exec. This should be done for MAP_SHARED mappings, for example, since they are not permanent forever, unlike the framebuffer for example.
47 lines
1.4 KiB
C++
47 lines
1.4 KiB
C++
#pragma once
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#include "memory/AddressSpace.h"
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#include "memory/Paging.h"
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enum Flags
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{
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ReadWrite = 1 << 0,
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User = 1 << 1,
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Execute = 1 << 2,
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OwnedByTask = 1 << 3,
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};
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namespace VMM
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{
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void init(); // Fetch page table from cr3
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void switch_to_user_address_space(AddressSpace& space);
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void switch_to_previous_user_address_space();
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void switch_back_to_kernel_address_space();
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void enter_syscall_context();
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void exit_syscall_context();
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void apply_address_space();
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bool is_using_kernel_address_space();
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void map(uint64_t vaddr, uint64_t paddr, int flags);
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void remap(uint64_t vaddr, int flags);
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void unmap(uint64_t vaddr);
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uint64_t get_physical(uint64_t vaddr);
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uint64_t get_flags(uint64_t vaddr);
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PageDirectoryEntry* find_pde(PageTable* root, uint64_t vaddr);
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PageDirectoryEntry* create_pde_if_not_exists(PageTable* root, uint64_t vaddr);
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void propagate_read_write(PageTable* root, uint64_t vaddr);
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void propagate_no_execute(PageTable* root, uint64_t vaddr);
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void propagate_user(PageTable* root, uint64_t vaddr);
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void flush_tlb(uint64_t addr);
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void decompose_vaddr(uint64_t vaddr, uint64_t& page_index, uint64_t& pt_index, uint64_t& pd_index,
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uint64_t& pdp_index);
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uint64_t recompose_vaddr(uint64_t page_index, uint64_t pt_index, uint64_t pd_index, uint64_t pdp_index);
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void install_kernel_page_directory_into_address_space(AddressSpace& space);
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}; |