NetBSD、FreeBSD、OpenBSD为何在pmap_growkernel的时候新增的页表项都没有置PG_G?

lllaaa

NetBSD的代码基本和OpenBSD的一样

/* * pmap_growkernel: increase usage of KVM space * * => we allocate new PTPs for the kernel and install them in all *    the pmaps on the system. */ vaddr_t pmap_growkernel(maxkvaddr)     vaddr_t maxkvaddr; {     struct pmap *kpm = pmap_kernel(), *pm;     int needed_kpde;   /* needed number of kernel PTPs */     int s;     paddr_t ptaddr;     needed_kpde = (u_int)(maxkvaddr - VM_MIN_KERNEL_ADDRESS + (NBPD-1))         / NBPD;     if (needed_kpde <= nkpde)         goto out;        /* we are OK */     /*      * whoops!   we need to add kernel PTPs      */     s = splhigh();    /* to be safe */     simple_lock(&kpm->pm_obj.vmobjlock);     for (/*null*/ ; nkpde < needed_kpde ; nkpde++) {         if (uvm.page_init_done == FALSE) {             /*              * we're growing the kernel pmap early (from              * uvm_pageboot_alloc()).  this case must be              * handled a little differently.              */             if (uvm_page_physget(&ptaddr) == FALSE)                 panic("pmap_growkernel: out of memory");             pmap_zero_page(ptaddr);             kpm->pm_pdir[PDSLOT_KERN + nkpde] =                 ptaddr | PG_RW | PG_V;             /* count PTP as resident */             kpm->pm_stats.resident_count++;             continue;         }         /*          * THIS *MUST* BE CODED SO AS TO WORK IN THE          * pmap_initialized == FALSE CASE!  WE MAY BE          * INVOKED WHILE pmap_init() IS RUNNING!          */         if (pmap_alloc_ptp(kpm, PDSLOT_KERN + nkpde) == NULL) {             panic("pmap_growkernel: alloc ptp failed");         }         /* PG_u not for kernel */         kpm->pm_pdir[PDSLOT_KERN + nkpde] &= ~PG_u;         /* distribute new kernel PTP to all active pmaps */         simple_lock(&pmaps_lock);         for (pm = pmaps.lh_first; pm != NULL;              pm = pm->pm_list.le_next) {             pm->pm_pdir[PDSLOT_KERN + nkpde] =                 kpm->pm_pdir[PDSLOT_KERN + nkpde];         }         /* Invalidate the PDP cache. */         pool_cache_invalidate(&pmap_pdp_cache);         pmap_pdp_cache_generation++;         simple_unlock(&pmaps_lock);     }     simple_unlock(&kpm->pm_obj.vmobjlock);     splx(s); out:     return (VM_MIN_KERNEL_ADDRESS + (nkpde * NBPD)); }

FreeBSD的

/* * grow the number of kernel page table entries, if needed */ void pmap_growkernel(vm_offset_t addr) {     struct pmap *pmap;     vm_paddr_t ptppaddr;     vm_page_t nkpg;     pd_entry_t newpdir;     pt_entry_t *pde;     mtx_assert(&kernel_map->system_mtx, MA_OWNED);     if (kernel_vm_end == 0) {         kernel_vm_end = KERNBASE;         nkpt = 0;         while (pdir_pde(PTD, kernel_vm_end)) {             kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);             nkpt++;             if (kernel_vm_end - 1 >= kernel_map->max_offset) {                 kernel_vm_end = kernel_map->max_offset;                 break;             }         }     }     addr = roundup2(addr, PAGE_SIZE * NPTEPG);     if (addr - 1 >= kernel_map->max_offset)         addr = kernel_map->max_offset;     while (kernel_vm_end < addr) {         if (pdir_pde(PTD, kernel_vm_end)) {             kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);             if (kernel_vm_end - 1 >= kernel_map->max_offset) {                 kernel_vm_end = kernel_map->max_offset;                 break;             }             continue;         }         /*          * This index is bogus, but out of the way          */         nkpg = vm_page_alloc(NULL, nkpt,             VM_ALLOC_NOOBJ | VM_ALLOC_SYSTEM | VM_ALLOC_WIRED);         if (!nkpg)             panic("pmap_growkernel: no memory to grow kernel");         nkpt++;         pmap_zero_page(nkpg);         ptppaddr = VM_PAGE_TO_PHYS(nkpg);         newpdir = (pd_entry_t) (ptppaddr | PG_V | PG_RW | PG_A | PG_M);         pdir_pde(PTD, kernel_vm_end) = newpdir;         mtx_lock_spin(&allpmaps_lock);         LIST_FOREACH(pmap, &allpmaps, pm_list) {             pde = pmap_pde(pmap, kernel_vm_end);             pde_store(pde, newpdir);         }         mtx_unlock_spin(&allpmaps_lock);         kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);         if (kernel_vm_end - 1 >= kernel_map->max_offset) {             kernel_vm_end = kernel_map->max_offset;             break;         }     } }

我的理解是,内核空间总是在最高的1G.在切换CR3的时候TLB里有关内核空间的项目不用被刷新,所以内核空间的页表项都要设置上Global标志PG_G.

但是看样子这几个BSD都能没有设置.不知道出于何种考虑.

[ 本帖最后由 lllaaa 于 2007-10-6 18:54 编辑 ]