mirror of
https://github.com/taigrr/gopher-os
synced 2025-01-18 04:43:13 -08:00
319f868a14
The page table walker provides a mechanism for accessing the individual page table entries that correspond to a particular virtual memory address. This implementation will serve as the basis for implementing page mapping/unmapping and virtual to physical address translation.
57 lines
2.2 KiB
Go
57 lines
2.2 KiB
Go
package vmm
|
|
|
|
import (
|
|
"unsafe"
|
|
|
|
"github.com/achilleasa/gopher-os/kernel/mem"
|
|
)
|
|
|
|
var (
|
|
// ptePointerFn returns a pointer to the supplied entry address. It is
|
|
// used by tests to override the generated page table entry pointers so
|
|
// walk() can be properly tested. When compiling the kernel this function
|
|
// will be automatically inlined.
|
|
ptePtrFn = func(entryAddr uintptr) unsafe.Pointer {
|
|
return unsafe.Pointer(entryAddr)
|
|
}
|
|
)
|
|
|
|
// pageTableWalker is a function that can be passed to the walk method. The
|
|
// function receives the current page level and page table entry as its
|
|
// arguments. If the function returns false, then the page walk is aborted.
|
|
type pageTableWalker func(pteLevel uint8, pte *pageTableEntry) bool
|
|
|
|
// walk performs a page table walk for the given virtual address. It calls the
|
|
// suppplied walkFn with the page table entry that corresponds to each page
|
|
// table level. If walkFn returns an error then the walk is aborted and the
|
|
// error is returned to the caller.
|
|
func walk(virtAddr uintptr, walkFn pageTableWalker) {
|
|
var (
|
|
level uint8
|
|
tableAddr, entryAddr, entryIndex uintptr
|
|
ok bool
|
|
)
|
|
|
|
// tableAddr is initially set to the recursively mapped virtual address for the
|
|
// last entry in the top-most page table. Dereferencing a pointer to this address
|
|
// will allow us to access
|
|
for level, tableAddr = uint8(0), pdtVirtualAddr; level < pageLevels; level, tableAddr = level+1, entryAddr {
|
|
// Extract the bits from virtual address that correspond to the
|
|
// index in this level's page table
|
|
entryIndex = (virtAddr >> pageLevelShifts[level]) & ((1 << pageLevelBits[level]) - 1)
|
|
|
|
// By shifting the table virtual address left by pageLevelShifts[level] we add
|
|
// a new level of indirection to our recursive mapping allowing us to access
|
|
// the table pointed to by the page entry
|
|
entryAddr = tableAddr + (entryIndex << mem.PointerShift)
|
|
|
|
if ok = walkFn(level, (*pageTableEntry)(ptePtrFn(entryAddr))); !ok {
|
|
return
|
|
}
|
|
|
|
// Shift left by the number of bits for this paging level to get
|
|
// the virtual address of the table pointed to by entryAddr
|
|
entryAddr <<= pageLevelBits[level]
|
|
}
|
|
}
|