379 lines
9.3 KiB
C
379 lines
9.3 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 "memlayout.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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extern char data[]; // defined by kernel.ld
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pde_t *kpgdir; // for use in scheduler()
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struct segdesc gdt[NSEGS];
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// Set up CPU's kernel segment descriptors.
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// Run once on entry on each CPU.
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void
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seginit(void)
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{
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struct cpu *c;
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// Map "logical" addresses to virtual 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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// Return the address of the PTE in page table pgdir
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// that corresponds to virtual address va. If alloc!=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 alloc)
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{
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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*)p2v(PTE_ADDR(*pde));
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} else {
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if(!alloc || (pgtab = (pte_t*)kalloc()) == 0)
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return 0;
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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 = v2p(pgtab) | 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 virtual addresses starting at va that refer to
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// physical addresses starting at pa. va 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 *va, uint size, uint pa, int perm)
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{
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char *a, *last;
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pte_t *pte;
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a = (char*)PGROUNDDOWN((uint)va);
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last = (char*)PGROUNDDOWN(((uint)va) + size - 1);
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for(;;){
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if((pte = walkpgdir(pgdir, a, 1)) == 0)
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return -1;
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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 0;
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}
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// There is one page table per process, plus one that's used when
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// a CPU is not running any process (kpgdir). The kernel uses the
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// current process's page table during system calls and interrupts;
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// page protection bits prevent user code from using the kernel's
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// mappings.
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//
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// setupkvm() and exec() set up every page table like this:
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//
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// 0..KERNBASE: user memory (text+data+stack+heap), mapped to
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// phys memory allocated by the kernel
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// KERNBASE..KERNBASE+EXTMEM: mapped to 0..EXTMEM (for I/O space)
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// KERNBASE+EXTMEM..data: mapped to EXTMEM..V2P(data)
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// for the kernel's instructions and r/o data
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// data..KERNBASE+PHYSTOP: mapped to V2P(data)..PHYSTOP,
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// rw data + free physical memory
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// 0xfe000000..0: mapped direct (devices such as ioapic)
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//
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// The kernel allocates physical memory for its heap and for user memory
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// between V2P(end) and the end of physical memory (PHYSTOP)
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// (directly addressable from end..P2V(PHYSTOP)).
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// This table defines the kernel's mappings, which are present in
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// every process's page table.
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static struct kmap {
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void *virt;
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uint phys_start;
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uint phys_end;
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int perm;
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} kmap[] = {
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{ (void*)KERNBASE, 0, EXTMEM, PTE_W}, // I/O space
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{ (void*)KERNLINK, V2P(KERNLINK), V2P(data), 0}, // kern text+rodata
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{ (void*)data, V2P(data), PHYSTOP, PTE_W}, // kern data+memory
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{ (void*)DEVSPACE, DEVSPACE, 0, PTE_W}, // more devices
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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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struct kmap *k;
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if((pgdir = (pde_t*)kalloc()) == 0)
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return 0;
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memset(pgdir, 0, PGSIZE);
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if (p2v(PHYSTOP) > (void*)DEVSPACE)
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panic("PHYSTOP too high");
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for(k = kmap; k < &kmap[NELEM(kmap)]; k++)
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if(mappages(pgdir, k->virt, k->phys_end - k->phys_start,
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(uint)k->phys_start, k->perm) < 0)
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return 0;
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return pgdir;
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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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switchkvm();
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}
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// Switch h/w page table register to the kernel-only page table,
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// for when no process is running.
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void
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switchkvm(void)
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{
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lcr3(v2p(kpgdir)); // switch to the kernel page table
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}
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// Switch TSS and h/w page table to correspond 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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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");
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lcr3(v2p(p->pgdir)); // switch to new address space
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popcli();
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}
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// Load the initcode into address 0 of pgdir.
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// sz must be less than a page.
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void
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inituvm(pde_t *pgdir, char *init, uint sz)
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{
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char *mem;
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if(sz >= PGSIZE)
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panic("inituvm: more than a page");
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mem = kalloc();
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memset(mem, 0, PGSIZE);
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mappages(pgdir, 0, PGSIZE, v2p(mem), PTE_W|PTE_U);
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memmove(mem, init, sz);
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}
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// Load a program segment into pgdir. addr must be page-aligned
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// and the pages from addr to addr+sz must already be mapped.
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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");
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for(i = 0; i < sz; i += PGSIZE){
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if((pte = walkpgdir(pgdir, addr+i, 0)) == 0)
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panic("loaduvm: address should exist");
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pa = PTE_ADDR(*pte);
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if(sz - i < PGSIZE)
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n = sz - i;
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else
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n = PGSIZE;
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if(readi(ip, p2v(pa), offset+i, n) != n)
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return -1;
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}
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return 0;
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}
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// Allocate page tables and physical memory to grow process from oldsz to
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// newsz, which need not be page aligned. Returns new size or 0 on error.
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int
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allocuvm(pde_t *pgdir, uint oldsz, uint newsz)
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{
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char *mem;
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uint a;
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if(newsz >= KERNBASE)
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return 0;
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if(newsz < oldsz)
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return oldsz;
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a = PGROUNDUP(oldsz);
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for(; a < newsz; a += PGSIZE){
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mem = kalloc();
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if(mem == 0){
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cprintf("allocuvm out of memory\n");
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deallocuvm(pgdir, newsz, oldsz);
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return 0;
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}
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memset(mem, 0, PGSIZE);
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mappages(pgdir, (char*)a, PGSIZE, v2p(mem), PTE_W|PTE_U);
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}
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return newsz;
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}
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// Deallocate user pages to bring the process size from oldsz to
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// newsz. oldsz and newsz need not be page-aligned, nor does newsz
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// need to be less than oldsz. oldsz can be larger than the actual
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// process size. Returns the new process size.
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int
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deallocuvm(pde_t *pgdir, uint oldsz, uint newsz)
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{
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pte_t *pte;
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uint a, pa;
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if(newsz >= oldsz)
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return oldsz;
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a = PGROUNDUP(newsz);
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for(; a < oldsz; a += PGSIZE){
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pte = walkpgdir(pgdir, (char*)a, 0);
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if(!pte)
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a += (NPTENTRIES - 1) * PGSIZE;
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else if((*pte & PTE_P) != 0){
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pa = PTE_ADDR(*pte);
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if(pa == 0)
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panic("kfree");
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char *v = p2v(pa);
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kfree(v);
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*pte = 0;
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}
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}
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return newsz;
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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;
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if(pgdir == 0)
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panic("freevm: no pgdir");
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deallocuvm(pgdir, KERNBASE, 0);
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for(i = 0; i < NPDENTRIES; i++){
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if(pgdir[i] & PTE_P){
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char * v = p2v(PTE_ADDR(pgdir[i]));
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kfree(v);
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}
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}
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kfree((char*)pgdir);
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}
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// Clear PTE_U on a page. Used to create an inaccessible
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// page beneath the user stack.
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void
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clearpteu(pde_t *pgdir, char *uva)
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{
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pte_t *pte;
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pte = walkpgdir(pgdir, uva, 0);
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if(pte == 0)
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panic("clearpteu");
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*pte &= ~PTE_U;
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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;
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pte_t *pte;
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uint pa, i, flags;
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char *mem;
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if((d = setupkvm()) == 0)
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return 0;
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for(i = 0; i < sz; i += PGSIZE){
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if((pte = walkpgdir(pgdir, (void *) i, 0)) == 0)
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panic("copyuvm: pte should exist");
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if(!(*pte & PTE_P))
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panic("copyuvm: page not present");
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pa = PTE_ADDR(*pte);
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flags = PTE_FLAGS(*pte);
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if((mem = kalloc()) == 0)
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goto bad;
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memmove(mem, (char*)p2v(pa), PGSIZE);
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if(mappages(d, (void*)i, PGSIZE, v2p(mem), flags) < 0)
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goto bad;
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}
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return d;
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bad:
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freevm(d);
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return 0;
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}
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//PAGEBREAK!
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// Map user virtual address to kernel address.
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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;
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pte = walkpgdir(pgdir, uva, 0);
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if((*pte & PTE_P) == 0)
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return 0;
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if((*pte & PTE_U) == 0)
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return 0;
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return (char*)p2v(PTE_ADDR(*pte));
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}
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// Copy len bytes from p to user address va in page table pgdir.
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// Most useful when pgdir is not the current page table.
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// uva2ka ensures this only works for PTE_U pages.
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int
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copyout(pde_t *pgdir, uint va, void *p, uint len)
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{
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char *buf, *pa0;
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uint n, va0;
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buf = (char*)p;
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while(len > 0){
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va0 = (uint)PGROUNDDOWN(va);
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pa0 = uva2ka(pgdir, (char*)va0);
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if(pa0 == 0)
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return -1;
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n = PGSIZE - (va - va0);
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if(n > len)
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n = len;
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memmove(pa0 + (va - va0), buf, n);
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len -= n;
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buf += n;
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va = va0 + PGSIZE;
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}
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return 0;
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}
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