iso9660fs: initialize buffer cache

[minix.git] / kernel / arch / arm / memory.c

#include "kernel/kernel.h"
#include "kernel/proc.h"
#include "kernel/vm.h"

#include <machine/vm.h>

#include <minix/type.h>
#include <minix/syslib.h>
#include <minix/cpufeature.h>
#include <string.h>
#include <assert.h>
#include <signal.h>
#include <stdlib.h>

#include <machine/vm.h>

#include "arch_proto.h"
#include "kernel/proto.h"
#include "kernel/debug.h"

phys_bytes device_mem_vaddr = 0;

#define HASPT(procptr) ((procptr)->p_seg.p_ttbr != 0)
static int nfreepdes = 0;
#define MAXFREEPDES     2
static int freepdes[MAXFREEPDES];

static u32_t phys_get32(phys_bytes v);

void mem_clear_mapcache(void)
{
        int i;
        for(i = 0; i < nfreepdes; i++) {
                struct proc *ptproc = get_cpulocal_var(ptproc);
                int pde = freepdes[i];
                u32_t *ptv;
                assert(ptproc);
                ptv = ptproc->p_seg.p_ttbr_v;
                assert(ptv);
                ptv[pde] = 0;
        }
}

/* This function sets up a mapping from within the kernel's address
 * space to any other area of memory, either straight physical
 * memory (pr == NULL) or a process view of memory, in 1MB windows.
 * I.e., it maps in 1MB chunks of virtual (or physical) address space
 * to 1MB chunks of kernel virtual address space.
 *
 * It recognizes pr already being in memory as a special case (no
 * mapping required).
 *
 * The target (i.e. in-kernel) mapping area is one of the freepdes[]
 * VM has earlier already told the kernel about that is available. It is
 * identified as the 'pde' parameter. This value can be chosen freely
 * by the caller, as long as it is in range (i.e. 0 or higher and corresonds
 * to a known freepde slot). It is up to the caller to keep track of which
 * freepde's are in use, and to determine which ones are free to use.
 *
 * The logical number supplied by the caller is translated into an actual
 * pde number to be used, and a pointer to it (linear address) is returned
 * for actual use by phys_copy or memset.
 */
static phys_bytes createpde(
        const struct proc *pr,  /* Requested process, NULL for physical. */
        const phys_bytes linaddr,/* Address after segment translation. */
        phys_bytes *bytes,      /* Size of chunk, function may truncate it. */
        int free_pde_idx,       /* index of the free slot to use */
        int *changed            /* If mapping is made, this is set to 1. */
        )
{
        u32_t pdeval;
        phys_bytes offset;
        int pde;

        assert(free_pde_idx >= 0 && free_pde_idx < nfreepdes);
        pde = freepdes[free_pde_idx];
        assert(pde >= 0 && pde < 4096);

        if(pr && ((pr == get_cpulocal_var(ptproc)) || iskernelp(pr))) {
                /* Process memory is requested, and
                 * it's a process that is already in current page table, or
                 * the kernel, which is always there.
                 * Therefore linaddr is valid directly, with the requested
                 * size.
                 */
                return linaddr;
        }

        if(pr) {
                /* Requested address is in a process that is not currently
                 * accessible directly. Grab the PDE entry of that process'
                 * page table that corresponds to the requested address.
                 */
                assert(pr->p_seg.p_ttbr_v);
                pdeval = pr->p_seg.p_ttbr_v[ARM_VM_PDE(linaddr)];
        } else {
                /* Requested address is physical. Make up the PDE entry. */
                pdeval = (linaddr & ARM_VM_SECTION_MASK) |
                        ARM_VM_SECTION |
                        ARM_VM_SECTION_DOMAIN | ARM_VM_SECTION_USER;
        }

        /* Write the pde value that we need into a pde that the kernel
         * can access, into the currently loaded page table so it becomes
         * visible.
         */
        assert(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v);
        if(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v[pde] != pdeval) {
                get_cpulocal_var(ptproc)->p_seg.p_ttbr_v[pde] = pdeval;
                *changed = 1;
        }

        /* Memory is now available, but only the 1MB window of virtual
         * address space that we have mapped; calculate how much of
         * the requested range is visible and return that in *bytes,
         * if that is less than the requested range.
         */
        offset = linaddr & ARM_VM_OFFSET_MASK_1MB; /* Offset in 1MB window. */
        *bytes = MIN(*bytes, ARM_BIG_PAGE_SIZE - offset);

        /* Return the linear address of the start of the new mapping. */
        return ARM_BIG_PAGE_SIZE*pde + offset;
}


/*===========================================================================*
 *                           check_resumed_caller                            *
 *===========================================================================*/
static int check_resumed_caller(struct proc *caller)
{
        /* Returns the result from VM if caller was resumed, otherwise OK. */
        if (caller && (caller->p_misc_flags & MF_KCALL_RESUME)) {
                assert(caller->p_vmrequest.vmresult != VMSUSPEND);
                return caller->p_vmrequest.vmresult;
        }

        return OK;
}
  
/*===========================================================================*
 *                              lin_lin_copy                                 *
 *===========================================================================*/
static int lin_lin_copy(struct proc *srcproc, vir_bytes srclinaddr, 
        struct proc *dstproc, vir_bytes dstlinaddr, vir_bytes bytes)
{
        u32_t addr;
        proc_nr_t procslot;

        assert(get_cpulocal_var(ptproc));
        assert(get_cpulocal_var(proc_ptr));
        assert(read_ttbr0() == get_cpulocal_var(ptproc)->p_seg.p_ttbr);

        procslot = get_cpulocal_var(ptproc)->p_nr;

        assert(procslot >= 0 && procslot < ARM_VM_DIR_ENTRIES);

        if(srcproc) assert(!RTS_ISSET(srcproc, RTS_SLOT_FREE));
        if(dstproc) assert(!RTS_ISSET(dstproc, RTS_SLOT_FREE));
        assert(!RTS_ISSET(get_cpulocal_var(ptproc), RTS_SLOT_FREE));
        assert(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v);
        if(srcproc) assert(!RTS_ISSET(srcproc, RTS_VMINHIBIT));
        if(dstproc) assert(!RTS_ISSET(dstproc, RTS_VMINHIBIT));

        while(bytes > 0) {
                phys_bytes srcptr, dstptr;
                vir_bytes chunk = bytes;
                int changed = 0;

#ifdef CONFIG_SMP
                unsigned cpu = cpuid;

                if (srcproc && GET_BIT(srcproc->p_stale_tlb, cpu)) {
                        changed = 1;
                        UNSET_BIT(srcproc->p_stale_tlb, cpu);
                }
                if (dstproc && GET_BIT(dstproc->p_stale_tlb, cpu)) {
                        changed = 1;
                        UNSET_BIT(dstproc->p_stale_tlb, cpu);
                }
#endif

                /* Set up 1MB ranges. */
                srcptr = createpde(srcproc, srclinaddr, &chunk, 0, &changed);
                dstptr = createpde(dstproc, dstlinaddr, &chunk, 1, &changed);
                if(changed) {
                        reload_ttbr0();
                        refresh_tlb();
                }
                /* Copy pages. */
                PHYS_COPY_CATCH(srcptr, dstptr, chunk, addr);

                if(addr) {
                        /* If addr is nonzero, a page fault was caught. */

                        if(addr >= srcptr && addr < (srcptr + chunk)) {
                                return EFAULT_SRC;
                        }
                        if(addr >= dstptr && addr < (dstptr + chunk)) {
                                return EFAULT_DST;
                        }

                        panic("lin_lin_copy fault out of range");

                        /* Not reached. */
                        return EFAULT;
                }

                /* Update counter and addresses for next iteration, if any. */
                bytes -= chunk;
                srclinaddr += chunk;
                dstlinaddr += chunk;
        }

        if(srcproc) assert(!RTS_ISSET(srcproc, RTS_SLOT_FREE));
        if(dstproc) assert(!RTS_ISSET(dstproc, RTS_SLOT_FREE));
        assert(!RTS_ISSET(get_cpulocal_var(ptproc), RTS_SLOT_FREE));
        assert(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v);

        return OK;
}

static u32_t phys_get32(phys_bytes addr)
{
        const u32_t v;
        int r;

        if((r=lin_lin_copy(NULL, addr, 
                proc_addr(SYSTEM), (phys_bytes) &v, sizeof(v))) != OK) {
                panic("lin_lin_copy for phys_get32 failed: %d",  r);
        }

        return v;
}

/*===========================================================================*
 *                              umap_virtual                                 *
 *===========================================================================*/
phys_bytes umap_virtual(rp, seg, vir_addr, bytes)
register struct proc *rp;       /* pointer to proc table entry for process */
int seg;                        /* T, D, or S segment */
vir_bytes vir_addr;             /* virtual address in bytes within the seg */
vir_bytes bytes;                /* # of bytes to be copied */
{
        phys_bytes phys = 0;

        if(vm_lookup(rp, vir_addr, &phys, NULL) != OK) {
                printf("SYSTEM:umap_virtual: vm_lookup of %s: seg 0x%x: 0x%lx failed\n", rp->p_name, seg, vir_addr);
                phys = 0;
        } else {
                if(phys == 0)
                        panic("vm_lookup returned phys: %d",  phys);
        }

        if(phys == 0) {
                printf("SYSTEM:umap_virtual: lookup failed\n");
                return 0;
        }

        /* Now make sure addresses are contiguous in physical memory
         * so that the umap makes sense.
         */
        if(bytes > 0 && vm_lookup_range(rp, vir_addr, NULL, bytes) != bytes) {
                printf("umap_virtual: %s: %lu at 0x%lx (vir 0x%lx) not contiguous\n",
                        rp->p_name, bytes, vir_addr, vir_addr);
                return 0;
        }

        /* phys must be larger than 0 (or the caller will think the call
         * failed), and address must not cross a page boundary.
         */
        assert(phys);

        return phys;
}


/*===========================================================================*
 *                              vm_lookup                                    *
 *===========================================================================*/
int vm_lookup(const struct proc *proc, const vir_bytes virtual,
 phys_bytes *physical, u32_t *ptent)
{
        u32_t *root, *pt;
        int pde, pte;
        u32_t pde_v, pte_v;

        assert(proc);
        assert(physical);
        assert(!isemptyp(proc));
        assert(HASPT(proc));

        /* Retrieve page directory entry. */
        root = (u32_t *) proc->p_seg.p_ttbr;
        assert(!((u32_t) root % ARM_PAGEDIR_SIZE));
        pde = ARM_VM_PDE(virtual);
        assert(pde >= 0 && pde < ARM_VM_DIR_ENTRIES);
        pde_v = phys_get32((u32_t) (root + pde));

        if(!(pde_v & ARM_VM_PDE_PRESENT)) {
                return EFAULT;
        }

        /* We don't expect to ever see this. */
        if(pde_v & ARM_VM_BIGPAGE) {
                *physical = pde_v & ARM_VM_SECTION_MASK;
                if(ptent) *ptent = pde_v;
                *physical += virtual & ARM_VM_OFFSET_MASK_1MB;
        } else {
                /* Retrieve page table entry. */
                pt = (u32_t *) (pde_v & ARM_VM_PDE_MASK);
                assert(!((u32_t) pt % ARM_PAGETABLE_SIZE));
                pte = ARM_VM_PTE(virtual);
                assert(pte >= 0 && pte < ARM_VM_PT_ENTRIES);
                pte_v = phys_get32((u32_t) (pt + pte));
                if(!(pte_v & ARM_VM_PTE_PRESENT)) {
                        return EFAULT;
                }

                if(ptent) *ptent = pte_v;

                /* Actual address now known; retrieve it and add page offset. */
                *physical = pte_v & ARM_VM_PTE_MASK;
                *physical += virtual % ARM_PAGE_SIZE;
        }

        return OK;
}

/*===========================================================================*
 *                              vm_lookup_range                              *
 *===========================================================================*/
size_t vm_lookup_range(const struct proc *proc, vir_bytes vir_addr,
        phys_bytes *phys_addr, size_t bytes)
{
        /* Look up the physical address corresponding to linear virtual address
         * 'vir_addr' for process 'proc'. Return the size of the range covered
         * by contiguous physical memory starting from that address; this may
         * be anywhere between 0 and 'bytes' inclusive. If the return value is
         * nonzero, and 'phys_addr' is non-NULL, 'phys_addr' will be set to the
         * base physical address of the range. 'vir_addr' and 'bytes' need not
         * be page-aligned, but the caller must have verified that the given
         * linear range is valid for the given process at all.
         */
        phys_bytes phys, next_phys;
        size_t len;

        assert(proc);
        assert(bytes > 0);
        assert(HASPT(proc));

        /* Look up the first page. */
        if (vm_lookup(proc, vir_addr, &phys, NULL) != OK)
                return 0;

        if (phys_addr != NULL)
                *phys_addr = phys;

        len = ARM_PAGE_SIZE - (vir_addr % ARM_PAGE_SIZE);
        vir_addr += len;
        next_phys = phys + len;

        /* Look up any next pages and test physical contiguity. */
        while (len < bytes) {
                if (vm_lookup(proc, vir_addr, &phys, NULL) != OK)
                        break;

                if (next_phys != phys)
                        break;

                len += ARM_PAGE_SIZE;
                vir_addr += ARM_PAGE_SIZE;
                next_phys += ARM_PAGE_SIZE;
        }

        /* We might now have overshot the requested length somewhat. */
        return MIN(bytes, len);
}

/*===========================================================================*
 *                              vm_suspend                                *
 *===========================================================================*/
static void vm_suspend(struct proc *caller, const struct proc *target,
        const vir_bytes linaddr, const vir_bytes len, const int type)
{
        /* This range is not OK for this process. Set parameters  
         * of the request and notify VM about the pending request. 
         */                                                             
        assert(!RTS_ISSET(caller, RTS_VMREQUEST));
        assert(!RTS_ISSET(target, RTS_VMREQUEST));

        RTS_SET(caller, RTS_VMREQUEST);

        caller->p_vmrequest.req_type = VMPTYPE_CHECK;
        caller->p_vmrequest.target = target->p_endpoint;
        caller->p_vmrequest.params.check.start = linaddr;
        caller->p_vmrequest.params.check.length = len;
        caller->p_vmrequest.params.check.writeflag = 1;
        caller->p_vmrequest.type = type;
                                                        
        /* Connect caller on vmrequest wait queue. */   
        if(!(caller->p_vmrequest.nextrequestor = vmrequest))
                if(OK != send_sig(VM_PROC_NR, SIGKMEM))
                        panic("send_sig failed");
        vmrequest = caller;
}

/*===========================================================================*
 *                              vm_check_range                               *
 *===========================================================================*/
int vm_check_range(struct proc *caller, struct proc *target,
        vir_bytes vir_addr, size_t bytes)
{
        /* Public interface to vm_suspend(), for use by kernel calls. On behalf
         * of 'caller', call into VM to check linear virtual address range of
         * process 'target', starting at 'vir_addr', for 'bytes' bytes. This
         * function assumes that it will called twice if VM returned an error
         * the first time (since nothing has changed in that case), and will
         * then return the error code resulting from the first call. Upon the
         * first call, a non-success error code is returned as well.
         */
        int r;

        if ((caller->p_misc_flags & MF_KCALL_RESUME) &&
                        (r = caller->p_vmrequest.vmresult) != OK)
                return r;

        vm_suspend(caller, target, vir_addr, bytes, VMSTYPE_KERNELCALL);

        return VMSUSPEND;
}

/*===========================================================================*
 *                              delivermsg                                *
 *===========================================================================*/
void delivermsg(struct proc *rp)
{
        int r = OK;

        assert(rp->p_misc_flags & MF_DELIVERMSG);
        assert(rp->p_delivermsg.m_source != NONE);

        if (copy_msg_to_user(&rp->p_delivermsg,
                                (message *) rp->p_delivermsg_vir)) {
                printf("WARNING wrong user pointer 0x%08lx from "
                                "process %s / %d\n",
                                rp->p_delivermsg_vir,
                                rp->p_name,
                                rp->p_endpoint);
                r = EFAULT;
        }

        /* Indicate message has been delivered; address is 'used'. */
        rp->p_delivermsg.m_source = NONE;
        rp->p_misc_flags &= ~MF_DELIVERMSG;

        if(!(rp->p_misc_flags & MF_CONTEXT_SET)) {
                rp->p_reg.retreg = r;
        }
}

/*===========================================================================*
 *                                 vmmemset                                  *
 *===========================================================================*/
int vm_memset(struct proc* caller, endpoint_t who, phys_bytes ph, int c,
        phys_bytes count)
{
        u32_t pattern;
        struct proc *whoptr = NULL;
        phys_bytes cur_ph = ph;
        phys_bytes left = count;
        phys_bytes ptr, chunk, pfa = 0;
        int new_ttbr, r = OK;

        if ((r = check_resumed_caller(caller)) != OK)
                return r;

        /* NONE for physical, otherwise virtual */
        if (who != NONE && !(whoptr = endpoint_lookup(who)))
                return ESRCH;

        c &= 0xFF;
        pattern = c | (c << 8) | (c << 16) | (c << 24);

        assert(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v);
        assert(!catch_pagefaults);
        catch_pagefaults = 1;

        /* We can memset as many bytes as we have remaining,
         * or as many as remain in the 1MB chunk we mapped in.
         */
        while (left > 0) {
                new_ttbr = 0;
                chunk = left;
                ptr = createpde(whoptr, cur_ph, &chunk, 0, &new_ttbr);

                if (new_ttbr) {
                        reload_ttbr0();
                        refresh_tlb();
                }
                /* If a page fault happens, pfa is non-null */
                if ((pfa = phys_memset(ptr, pattern, chunk))) {

                        /* If a process pagefaults, VM may help out */
                        if (whoptr) {
                                vm_suspend(caller, whoptr, ph, count,
                                                   VMSTYPE_KERNELCALL);
                                assert(catch_pagefaults);
                                catch_pagefaults = 0;
                                return VMSUSPEND;
                        }

                        /* Pagefault when phys copying ?! */
                        panic("vm_memset: pf %lx addr=%lx len=%lu\n",
                                                pfa , ptr, chunk);
                }

                cur_ph += chunk;
                left -= chunk;
        }

        assert(get_cpulocal_var(ptproc)->p_seg.p_ttbr_v);
        assert(catch_pagefaults);
        catch_pagefaults = 0;

        return OK;
}

/*===========================================================================*
 *                              virtual_copy_f                               *
 *===========================================================================*/
int virtual_copy_f(caller, src_addr, dst_addr, bytes, vmcheck)
struct proc * caller;
struct vir_addr *src_addr;      /* source virtual address */
struct vir_addr *dst_addr;      /* destination virtual address */
vir_bytes bytes;                /* # of bytes to copy  */
int vmcheck;                    /* if nonzero, can return VMSUSPEND */
{
/* Copy bytes from virtual address src_addr to virtual address dst_addr. */
  struct vir_addr *vir_addr[2]; /* virtual source and destination address */
  int i, r;
  struct proc *procs[2];

  assert((vmcheck && caller) || (!vmcheck && !caller));

  /* Check copy count. */
  if (bytes <= 0) return(EDOM);

  /* Do some more checks and map virtual addresses to physical addresses. */
  vir_addr[_SRC_] = src_addr;
  vir_addr[_DST_] = dst_addr;

  for (i=_SRC_; i<=_DST_; i++) {
        endpoint_t proc_e = vir_addr[i]->proc_nr_e;
        int proc_nr;
        struct proc *p;

        if(proc_e == NONE) {
                p = NULL;
        } else {
                if(!isokendpt(proc_e, &proc_nr)) {
                        printf("virtual_copy: no reasonable endpoint\n");
                        return ESRCH;
                }
                p = proc_addr(proc_nr);
        }

        procs[i] = p;
  }

  if ((r = check_resumed_caller(caller)) != OK)
        return r;

  if((r=lin_lin_copy(procs[_SRC_], vir_addr[_SRC_]->offset,
        procs[_DST_], vir_addr[_DST_]->offset, bytes)) != OK) {
        struct proc *target = NULL;
        phys_bytes lin;
        if(r != EFAULT_SRC && r != EFAULT_DST)
                panic("lin_lin_copy failed: %d",  r);
        if(!vmcheck || !caller) {
                return r;
        }

        if(r == EFAULT_SRC) {
                lin = vir_addr[_SRC_]->offset;
                target = procs[_SRC_];
        } else if(r == EFAULT_DST) {
                lin = vir_addr[_DST_]->offset;
                target = procs[_DST_];
        } else {
                panic("r strange: %d",  r);
        }

        assert(caller);
        assert(target);

        vm_suspend(caller, target, lin, bytes, VMSTYPE_KERNELCALL);
        return VMSUSPEND;
  }

  return OK;
}

/*===========================================================================*
 *                              data_copy                                    *
 *===========================================================================*/
int data_copy(const endpoint_t from_proc, const vir_bytes from_addr,
        const endpoint_t to_proc, const vir_bytes to_addr,
        size_t bytes)
{
  struct vir_addr src, dst;

  src.offset = from_addr;
  dst.offset = to_addr;
  src.proc_nr_e = from_proc;
  dst.proc_nr_e = to_proc;
  assert(src.proc_nr_e != NONE);
  assert(dst.proc_nr_e != NONE);

  return virtual_copy(&src, &dst, bytes);
}

/*===========================================================================*
 *                              data_copy_vmcheck                            *
 *===========================================================================*/
int data_copy_vmcheck(struct proc * caller,
        const endpoint_t from_proc, const vir_bytes from_addr,
        const endpoint_t to_proc, const vir_bytes to_addr,
        size_t bytes)
{
  struct vir_addr src, dst;

  src.offset = from_addr;
  dst.offset = to_addr;
  src.proc_nr_e = from_proc;
  dst.proc_nr_e = to_proc;
  assert(src.proc_nr_e != NONE);
  assert(dst.proc_nr_e != NONE);

  return virtual_copy_vmcheck(caller, &src, &dst, bytes);
}

void memory_init(void)
{
        assert(nfreepdes == 0);

        freepdes[nfreepdes++] = kinfo.freepde_start++;
        freepdes[nfreepdes++] = kinfo.freepde_start++;

        assert(kinfo.freepde_start < ARM_VM_DIR_ENTRIES);
        assert(nfreepdes == 2);
        assert(nfreepdes <= MAXFREEPDES);
}

/*===========================================================================*
 *                              arch_proc_init                               *
 *===========================================================================*/
void arch_proc_init(struct proc *pr, const u32_t ip, const u32_t sp, char *name)
{
        arch_proc_reset(pr);
        strcpy(pr->p_name, name);

        /* set custom state we know */
        pr->p_reg.pc = ip;
        pr->p_reg.sp = sp;
}

static int device_mem_mapping_index = -1,
        usermapped_glo_index = -1,
        usermapped_index = -1, first_um_idx = -1;

char *device_mem;

extern char usermapped_start, usermapped_end, usermapped_nonglo_start;

int arch_phys_map(const int index,
                        phys_bytes *addr,
                        phys_bytes *len,
                        int *flags)
{
        static int first = 1;
        int freeidx = 0;
        u32_t glo_len = (u32_t) &usermapped_nonglo_start -
                        (u32_t) &usermapped_start;

        if(first) {
                device_mem_mapping_index = freeidx++;
                if(glo_len > 0) {
                        usermapped_glo_index = freeidx++;
                }

                usermapped_index = freeidx++;
                first_um_idx = usermapped_index;
                if(usermapped_glo_index != -1)
                        first_um_idx = usermapped_glo_index;
                first = 0;
        }

        if(index == usermapped_glo_index) {
                *addr = vir2phys(&usermapped_start);
                *len = glo_len;
                *flags = VMMF_USER | VMMF_GLO;
                return OK;
        }
        else if(index == usermapped_index) {
                *addr = vir2phys(&usermapped_nonglo_start);
                *len = (u32_t) &usermapped_end -
                        (u32_t) &usermapped_nonglo_start;
                *flags = VMMF_USER;
                return OK;
        }
        else if (index == device_mem_mapping_index) {
                /* map device memory */
                *addr = 0x48000000;
                *len =  0x02000000;
                *flags = VMMF_UNCACHED | VMMF_WRITE;
                return OK;
        }

        return EINVAL;
}

int arch_phys_map_reply(const int index, const vir_bytes addr)
{
        if(index == first_um_idx) {
                u32_t usermapped_offset;
                assert(addr > (u32_t) &usermapped_start);
                usermapped_offset = addr - (u32_t) &usermapped_start;
                memset(&minix_kerninfo, 0, sizeof(minix_kerninfo));
#define FIXEDPTR(ptr) (void *) ((u32_t)ptr + usermapped_offset)
#define FIXPTR(ptr) ptr = FIXEDPTR(ptr)
#define ASSIGN(minixstruct) minix_kerninfo.minixstruct = FIXEDPTR(&minixstruct)
                ASSIGN(kinfo);
                ASSIGN(machine);
                ASSIGN(kmessages);
                ASSIGN(loadinfo);

                /* adjust the pointers of the functions and the struct
                 * itself to the user-accessible mapping
                 */
                minix_kerninfo.kerninfo_magic = KERNINFO_MAGIC;
                minix_kerninfo.minix_feature_flags = minix_feature_flags;
                minix_kerninfo_user = (vir_bytes) FIXEDPTR(&minix_kerninfo);

                return OK;
        }

        if(index == usermapped_index) return OK;

        if (index == device_mem_mapping_index) {
                device_mem_vaddr =  addr;
                return OK;
        }

        return EINVAL;
}

int arch_enable_paging(struct proc * caller)
{
        assert(caller->p_seg.p_ttbr);

        /* load caller's page table */
        switch_address_space(caller);

        device_mem = (char *) device_mem_vaddr;

        return OK;
}

void release_address_space(struct proc *pr)
{
        pr->p_seg.p_ttbr_v = NULL;
        refresh_tlb();
}