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Avoid repition in walkpgdir

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This commit is contained in:
Frans Kaashoek 2018-10-02 07:37:49 -04:00
parent 572e106e6f
commit 155c13b7f8
2 changed files with 24 additions and 60 deletions
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26
mmu.h
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@ -91,26 +91,22 @@ struct segdesc {
// +------+-------+--------------+----------+------------+-------------+
// \-PMX(va)-/\-PDPX(va)--/ \-PDX(va)-/ \-PTX(va)-/
#define PMX(va) (((uint64)(va) >> PML4XSHIFT) & PXMASK)
#define PDPX(va) (((uint64)(va) >> PDPXSHIFT) & PXMASK)
// page directory index
#define PDX(va) (((uint64)(va) >> PDXSHIFT) & PXMASK)
// page table index
#define PTX(va) (((uint64)(va) >> PTXSHIFT) & PXMASK)
// construct virtual address from indexes and offset
#define PGADDR(d, t, o) ((uint64)((d) << PDXSHIFT | (t) << PTXSHIFT | (o)))
// Page directory and page table constants.
#define NPDENTRIES 512 // # directory entries per page directory
#define NPTENTRIES 512 // # PTEs per page table
#define PGSIZE 4096 // bytes mapped by a page
#define PTXSHIFT 12 // offset of PTX in a linear address
#define PGSHIFT 12 // offset of PTX in a linear address
#define PDXSHIFT 21 // offset of PDX in a linear address
#define PDPXSHIFT 30 // offset of PDPX in a linear address
#define PML4XSHIFT 39 // offset of PML4X in a linear address
#define PXMASK 0X1FF
#define PXMASK 0x1FF
#define PXSHIFT(n) (PGSHIFT+(9*(n)))
#define PDX(va) (((uint64)(va) >> PDXSHIFT) & PXMASK)
#define PTX(va) (((uint64)(va) >> PGSHIFT) & PXMASK)
#define PX(n, va) ((((uint64) (va)) >> PXSHIFT(n)) & PXMASK)
#define L_PML4 3
// construct virtual address from indexes and offset
#define PGADDR(d, t, o) ((uint64)((d) << PDXSHIFT | (t) << PGSHIFT | (o)))
#define PGROUNDUP(sz) (((sz)+PGSIZE-1) & ~(PGSIZE-1))
#define PGROUNDDOWN(a) (((a)) & ~(PGSIZE-1))

58
vm.c
View file

@ -66,53 +66,21 @@ seginit(void)
static pte_t *
walkpgdir(pde_t *pml4, const void *va, int alloc)
{
pml4e_t *pml4e;
pdpe_t *pdp;
pdpe_t *pdpe;
pde_t *pgtab = pml4;
pde_t *pde;
pde_t *pd;
pte_t *pgtab;
// level 4
pml4e = &pml4[PMX(va)];
if(*pml4e & PTE_P)
pdp = (pdpe_t*)P2V(PTE_ADDR(*pml4e));
else {
if(!alloc || (pdp = (pdpe_t*)kalloc()) == 0)
return 0;
// Make sure all those PTE_P bits are zero.
memset(pdp, 0, PGSIZE);
// The permissions here are overly generous, but they can
// be further restricted by the permissions in the page table
// entries, if necessary.
*pml4e = V2P(pdp) | PTE_P | PTE_W | PTE_U;
int level;
for (level = L_PML4; level > 0; level--) {
pde = &pgtab[PX(level, va)];
if(*pde & PTE_P)
pgtab = (pte_t*)P2V(PTE_ADDR(*pde));
else {
if(!alloc || (pgtab = (pte_t*)kalloc()) == 0)
return 0;
memset(pgtab, 0, PGSIZE);
*pde = V2P(pgtab) | PTE_P | PTE_W | PTE_U;
}
}
// XXX avoid repetition
// level 3
pdpe = &pdp[PDPX(va)];
if(*pdpe & PTE_P)
pd = (pde_t*)P2V(PTE_ADDR(*pdpe));
else {
if(!alloc || (pd = (pde_t*)kalloc()) == 0)
return 0;
memset(pd, 0, PGSIZE);
*pdpe = V2P(pd) | PTE_P | PTE_W | PTE_U;
}
// level 2
pde = &pd[PDX(va)];
if(*pde & PTE_P)
pgtab = (pte_t*)P2V(PTE_ADDR(*pde));
else {
if(!alloc || (pgtab = (pte_t*)kalloc()) == 0)
return 0;
memset(pgtab, 0, PGSIZE);
*pde = V2P(pgtab) | PTE_P | PTE_W | PTE_U;
}
// level 1
return &pgtab[PTX(va)];
}