diff options
| -rw-r--r-- | vm.c | 16 |
1 files changed, 6 insertions, 10 deletions
@@ -92,10 +92,9 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, // The mappings from logical to virtual are one to one (i.e., // segmentation doesn't do anything). There is one page table per -// process, plus one that's used when a CPU is not running any -// process (kpgdir). A user process uses the same page table as -// the kernel; the page protection bits prevent it from using -// anything other than its memory. +// process, plus one that's used when a CPU is not running any process +// (kpgdir). A user process uses the same page table as the kernel; the +// page protection bits prevent it from accessing kernel memory. // // setupkvm() and exec() set up every page table like this: // 0..KERNBASE: user memory (text+data+stack+heap), mapped to some free @@ -108,10 +107,9 @@ mappages(pde_t *pgdir, void *va, uint size, uint pa, // 0xfe000000..0: mapped direct (devices such as ioapic) // // The kernel allocates memory for its heap and for user memory -// between kernend and the end of physical memory (PHYSTOP). -// The virtual address space of each user program includes the kernel -// (which is inaccessible in user mode). The user program sits in -// the bottom of the address space, and the kernel at the top at KERNBASE. +// between KERNBASE+end and the end of physical memory (PHYSTOP). +// The user program sits in the bottom of the address space, and the +// kernel at the top at KERNBASE. static struct kmap { void *virt; uint phys_start; @@ -134,14 +132,12 @@ setupkvm(char* (*alloc)(void)) if((pgdir = (pde_t*)alloc()) == 0) return 0; memset(pgdir, 0, PGSIZE); - k = kmap; if (p2v(PHYSTOP) > (void*)DEVSPACE) panic("PHYSTOP too high"); for(k = kmap; k < &kmap[NELEM(kmap)]; k++) if(mappages(pgdir, k->virt, k->phys_end - k->phys_start, (uint)k->phys_start, k->perm, alloc) < 0) return 0; - return pgdir; } |