383 lines
9.8 KiB
C
383 lines
9.8 KiB
C
#include "param.h"
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#include "types.h"
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#include "defs.h"
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#include "x86.h"
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#include "mmu.h"
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#include "proc.h"
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#include "elf.h"
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// The mappings from logical to linear are one to one (i.e.,
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// segmentation doesn't do anything).
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// There is one page table per process, plus one that's used
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// when a CPU is not running any process (kpgdir).
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// A user process uses the same page table as the kernel; the
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// page protection bits prevent it from using anything other
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// than its memory.
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//
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// setupkvm() and exec() set up every page table like this:
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// 0..640K : user memory (text, data, stack, heap)
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// 640K..1M : mapped direct (for IO space)
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// 1M..kernend : mapped direct (for the kernel's text and data)
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// kernend..PHYSTOP : mapped direct (kernel heap and user pages)
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// 0xfe000000..0 : mapped direct (devices such as ioapic)
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//
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// The kernel allocates memory for its heap and for user memory
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// between kernend and the end of physical memory (PHYSTOP).
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// The virtual address space of each user program includes the kernel
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// (which is inaccessible in user mode). The user program addresses
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// range from 0 till 640KB (USERTOP), which where the I/O hole starts
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// (both in physical memory and in the kernel's virtual address
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// space).
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#define PHYSTOP 0x1000000
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#define USERTOP 0xA0000
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static uint kerntext; // Linker starts kernel at 1MB
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static uint kerntsz;
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static uint kerndata;
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static uint kerndsz;
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static uint kernend;
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static uint freesz;
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static pde_t *kpgdir; // for use in scheduler()
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// return the address of the PTE in page table pgdir
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// that corresponds to linear address va. if create!=0,
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// create any required page table pages.
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static pte_t *
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walkpgdir(pde_t *pgdir, const void *va, int create)
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{
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uint r;
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pde_t *pde;
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pte_t *pgtab;
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pde = &pgdir[PDX(va)];
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if (*pde & PTE_P) {
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pgtab = (pte_t*) PTE_ADDR(*pde);
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} else if (!create || !(r = (uint) kalloc(PGSIZE)))
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return 0;
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else {
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pgtab = (pte_t*) r;
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// Make sure all those PTE_P bits are zero.
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memset(pgtab, 0, PGSIZE);
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// The permissions here are overly generous, but they can
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// be further restricted by the permissions in the page table
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// entries, if necessary.
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*pde = PADDR(r) | PTE_P | PTE_W | PTE_U;
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}
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return &pgtab[PTX(va)];
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}
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// create PTEs for linear addresses starting at la that refer to
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// physical addresses starting at pa. la and size might not
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// be page-aligned.
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static int
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mappages(pde_t *pgdir, void *la, uint size, uint pa, int perm)
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{
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char *first = PGROUNDDOWN(la);
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char *last = PGROUNDDOWN(la + size - 1);
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char *a = first;
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while(1){
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pte_t *pte = walkpgdir(pgdir, a, 1);
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if(pte == 0)
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return 0;
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if(*pte & PTE_P)
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panic("remap");
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*pte = pa | perm | PTE_P;
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if(a == last)
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break;
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a += PGSIZE;
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pa += PGSIZE;
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}
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return 1;
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}
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// Set up CPU's kernel segment descriptors.
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// Run once at boot time on each CPU.
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void
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ksegment(void)
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{
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struct cpu *c;
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// Map virtual addresses to linear addresses using identity map.
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// Cannot share a CODE descriptor for both kernel and user
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// because it would have to have DPL_USR, but the CPU forbids
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// an interrupt from CPL=0 to DPL=3.
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c = &cpus[cpunum()];
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c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0);
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c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
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c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, DPL_USER);
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c->gdt[SEG_UDATA] = SEG(STA_W, 0, 0xffffffff, DPL_USER);
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// map cpu, and curproc
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c->gdt[SEG_KCPU] = SEG(STA_W, &c->cpu, 8, 0);
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lgdt(c->gdt, sizeof(c->gdt));
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loadgs(SEG_KCPU << 3);
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// Initialize cpu-local storage.
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cpu = c;
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proc = 0;
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}
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// Switch h/w page table and TSS registers to point to process p.
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void
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switchuvm(struct proc *p)
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{
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pushcli();
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// Setup TSS
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cpu->gdt[SEG_TSS] = SEG16(STS_T32A, &cpu->ts, sizeof(cpu->ts)-1, 0);
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cpu->gdt[SEG_TSS].s = 0;
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cpu->ts.ss0 = SEG_KDATA << 3;
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cpu->ts.esp0 = (uint)proc->kstack + KSTACKSIZE;
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ltr(SEG_TSS << 3);
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if (p->pgdir == 0)
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panic("switchuvm: no pgdir\n");
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lcr3(PADDR(p->pgdir)); // switch to new address space
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popcli();
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}
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// Switch h/w page table register to the kernel-only page table, for when
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// no process is running.
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void
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switchkvm()
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{
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lcr3(PADDR(kpgdir)); // Switch to the kernel page table
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}
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// Set up kernel part of a page table.
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pde_t*
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setupkvm(void)
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{
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pde_t *pgdir;
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// Allocate page directory
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if (!(pgdir = (pde_t *) kalloc(PGSIZE)))
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return 0;
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memset(pgdir, 0, PGSIZE);
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// Map IO space from 640K to 1Mbyte
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if (!mappages(pgdir, (void *)USERTOP, 0x60000, USERTOP, PTE_W))
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return 0;
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// Map kernel text read-only
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if (!mappages(pgdir, (void *) kerntext, kerntsz, kerntext, 0))
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return 0;
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// Map kernel data read/write
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if (!mappages(pgdir, (void *) kerndata, kerndsz, kerndata, PTE_W))
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return 0;
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// Map dynamically-allocated memory read/write (kernel stacks, user mem)
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if (!mappages(pgdir, (void *) kernend, freesz, PADDR(kernend), PTE_W))
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return 0;
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// Map devices such as ioapic, lapic, ...
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if (!mappages(pgdir, (void *)0xFE000000, 0x2000000, 0xFE000000, PTE_W))
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return 0;
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return pgdir;
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}
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// return the physical address that a given user address
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// maps to. the result is also a kernel logical address,
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// since the kernel maps the physical memory allocated to user
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// processes directly.
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char*
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uva2ka(pde_t *pgdir, char *uva)
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{
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pte_t *pte = walkpgdir(pgdir, uva, 0);
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if (pte == 0) return 0;
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uint pa = PTE_ADDR(*pte);
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return (char *)pa;
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}
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// allocate sz bytes more memory for a process starting at the
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// given user address; allocates physical memory and page
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// table entries. addr and sz need not be page-aligned.
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// it is a no-op for any parts of the requested memory
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// that are already allocated.
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int
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allocuvm(pde_t *pgdir, char *addr, uint sz)
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{
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if (addr + sz > (char*)USERTOP)
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return 0;
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char *first = PGROUNDDOWN(addr);
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char *last = PGROUNDDOWN(addr + sz - 1);
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char *a;
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for(a = first; a <= last; a += PGSIZE){
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pte_t *pte = walkpgdir(pgdir, a, 0);
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if(pte == 0 || (*pte & PTE_P) == 0){
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char *mem = kalloc(PGSIZE);
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if(mem == 0){
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// XXX clean up?
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return 0;
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}
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memset(mem, 0, PGSIZE);
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mappages(pgdir, a, PGSIZE, PADDR(mem), PTE_W|PTE_U);
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}
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}
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return 1;
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}
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// deallocate some of the user pages, in response to sbrk()
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// with a negative argument. if addr is not page-aligned,
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// then only deallocates starting at the next page boundary.
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int
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deallocuvm(pde_t *pgdir, char *addr, uint sz)
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{
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if (addr + sz > (char*)USERTOP)
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return 0;
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char *first = (char*) PGROUNDUP((uint)addr);
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char *last = PGROUNDDOWN(addr + sz - 1);
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char *a;
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for(a = first; a <= last; a += PGSIZE){
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pte_t *pte = walkpgdir(pgdir, a, 0);
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if(pte && (*pte & PTE_P) != 0){
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uint pa = PTE_ADDR(*pte);
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if(pa == 0)
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panic("deallocuvm");
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kfree((void *) pa, PGSIZE);
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*pte = 0;
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}
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}
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return 1;
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}
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// free a page table and all the physical memory pages
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// in the user part.
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void
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freevm(pde_t *pgdir)
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{
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uint i, j, da;
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if (!pgdir)
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panic("freevm: no pgdir\n");
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for (i = 0; i < NPDENTRIES; i++) {
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da = PTE_ADDR(pgdir[i]);
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if (da != 0) {
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pte_t *pgtab = (pte_t*) da;
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for (j = 0; j < NPTENTRIES; j++) {
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if (pgtab[j] != 0) {
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uint pa = PTE_ADDR(pgtab[j]);
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uint va = PGADDR(i, j, 0);
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if (va < USERTOP) // user memory
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kfree((void *) pa, PGSIZE);
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pgtab[j] = 0;
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}
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}
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kfree((void *) da, PGSIZE);
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pgdir[i] = 0;
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}
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}
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kfree((void *) pgdir, PGSIZE);
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}
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int
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loaduvm(pde_t *pgdir, char *addr, struct inode *ip, uint offset, uint sz)
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{
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uint i, pa, n;
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pte_t *pte;
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if ((uint)addr % PGSIZE != 0)
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panic("loaduvm: addr must be page aligned\n");
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for (i = 0; i < sz; i += PGSIZE) {
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if (!(pte = walkpgdir(pgdir, addr+i, 0)))
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panic("loaduvm: address should exist\n");
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pa = PTE_ADDR(*pte);
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if (sz - i < PGSIZE) n = sz - i;
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else n = PGSIZE;
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if(readi(ip, (char *)pa, offset+i, n) != n)
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return 0;
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}
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return 1;
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}
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void
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inituvm(pde_t *pgdir, char *addr, char *init, uint sz)
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{
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uint i, pa, n, off;
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pte_t *pte;
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for (i = 0; i < sz; i += PGSIZE) {
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if (!(pte = walkpgdir(pgdir, (void *)(i+addr), 0)))
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panic("inituvm: pte should exist\n");
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off = (i+(uint)addr) % PGSIZE;
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pa = PTE_ADDR(*pte);
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if (sz - i < PGSIZE) n = sz - i;
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else n = PGSIZE;
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memmove((char *)pa+off, init+i, n);
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}
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}
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// given a parent process's page table, create a copy
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// of it for a child.
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pde_t*
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copyuvm(pde_t *pgdir, uint sz)
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{
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pde_t *d = setupkvm();
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pte_t *pte;
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uint pa, i;
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char *mem;
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if (!d) return 0;
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for (i = 0; i < sz; i += PGSIZE) {
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if (!(pte = walkpgdir(pgdir, (void *)i, 0)))
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panic("copyuvm: pte should exist\n");
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if(*pte & PTE_P){
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pa = PTE_ADDR(*pte);
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if (!(mem = kalloc(PGSIZE)))
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return 0;
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memmove(mem, (char *)pa, PGSIZE);
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if (!mappages(d, (void *)i, PGSIZE, PADDR(mem), PTE_W|PTE_U))
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return 0;
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}
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}
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return d;
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}
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// Gather information about physical memory layout.
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// Called once during boot.
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// Really should find out how much physical memory
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// there is rather than assuming PHYSTOP.
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void
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pminit(void)
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{
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extern char end[];
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struct proghdr *ph;
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struct elfhdr *elf = (struct elfhdr*)0x10000; // scratch space
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if (elf->magic != ELF_MAGIC || elf->phnum != 2)
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panic("pminit: need a text and data segment\n");
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ph = (struct proghdr*)((uchar*)elf + elf->phoff);
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kernend = ((uint)end + PGSIZE) & ~(PGSIZE-1);
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kerntext = ph[0].va;
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kerndata = ph[1].va;
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kerntsz = ph[0].memsz;
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kerndsz = ph[1].memsz;
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freesz = PHYSTOP - kernend;
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kinit((char *)kernend, freesz);
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}
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// Allocate one page table for the machine for the kernel address
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// space for scheduler processes.
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void
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kvmalloc(void)
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{
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kpgdir = setupkvm();
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}
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// Turn on paging.
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void
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vminit(void)
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{
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uint cr0;
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lcr3(PADDR(kpgdir));
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cr0 = rcr0();
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cr0 |= CR0_PE|CR0_PG|CR0_AM|CR0_WP|CR0_NE|CR0_TS|CR0_EM|CR0_MP;
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cr0 &= ~(CR0_TS|CR0_EM);
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lcr0(cr0);
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}
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