/* Copyright (C) 2004  David Decotigny
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.
    
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA. 
 */
 #include <sos/physmem.h>
 #include <sos/klibc.h>
 #include <sos/assert.h>
 
 #include "mm_context.h"
 
 #include "paging.h"
 
 
 /*
  * Important NOTICE concerning the use of the reference & occupation
  * counters of the physical pages by the "paging" subsystem:
  *   - All the kernel PT are SHARED. This means that as soon as one
  *     kernel PT belongs to one mm_context, it belongs to ALL the
  *     mm_contexts. We don't update the real reference count of the PT
  *     in this respect, because it would require to update the
  *     reference counts of ALL the kernel PTs as soon as a new
  *     mm_context is created, or as soon as a mm_context is
  *     suppressed. This way, the reference count is constant
  *     independently of the actual number of PD really sharing them.
  *   - We do NOT maintain the occupation count of the PDs. This would add
  *     some little overhead that is useless
  *   - We do maintain the occupation count of ALL the PTs: it represents the
  *     number of PTE allocated in the PT
  */
 
 
 /** The structure of a page directory entry. See Intel vol 3 section
     3.6.4 */
 struct x86_pde
 {
   sos_ui32_t present        :1; /* 1=PT mapped */
   sos_ui32_t write          :1; /* 0=read-only, 1=read/write */
   sos_ui32_t user           :1; /* 0=supervisor, 1=user */
   sos_ui32_t write_through  :1; /* 0=write-back, 1=write-through */
   sos_ui32_t cache_disabled :1; /* 1=cache disabled */
   sos_ui32_t accessed       :1; /* 1=read/write access since last clear */
   sos_ui32_t zero           :1; /* Intel reserved */
   sos_ui32_t page_size      :1; /* 0=4kB, 1=4MB or 2MB (depending on PAE) */
   sos_ui32_t global_page    :1; /* Ignored (Intel reserved) */
   sos_ui32_t custom         :3; /* Do what you want with them */
   sos_ui32_t pt_paddr       :20;
 } __attribute__ ((packed));
 
 
 /** Intermediate type to speed up PDE copy */
 typedef union {
   struct x86_pde pde;
   sos_ui32_t     ui32;
 } x86_pde_val_t;
 
 
 /** The structure of a page table entry. See Intel vol 3 section
     3.6.4 */
 struct x86_pte
 {
   sos_ui32_t present        :1; /* 1=PT mapped */
   sos_ui32_t write          :1; /* 0=read-only, 1=read/write */
   sos_ui32_t user           :1; /* 0=supervisor, 1=user */
   sos_ui32_t write_through  :1; /* 0=write-back, 1=write-through */
   sos_ui32_t cache_disabled :1; /* 1=cache disabled */
   sos_ui32_t accessed       :1; /* 1=read/write access since last clear */
   sos_ui32_t dirty          :1; /* 1=write access since last clear */
   sos_ui32_t zero           :1; /* Intel reserved */
   sos_ui32_t global_page    :1; /* 1=No TLB invalidation upon cr3 switch
                                    (when PG set in cr4) */
   sos_ui32_t custom         :3; /* Do what you want with them */
   sos_ui32_t paddr          :20;
 } __attribute__ ((packed));
 
 
 /** Intermediate type to speed up PTE copy */
 typedef union {
   struct x86_pte pte;
   sos_ui32_t     ui32;
 } x86_pte_val_t;
 
 
 /** Structure of the x86 CR3 register: the Page Directory Base
     Register. See Intel x86 doc Vol 3 section 2.5 */
 struct x86_pdbr
 {
   sos_ui32_t zero1          :3; /* Intel reserved */
   sos_ui32_t write_through  :1; /* 0=write-back, 1=write-through */
   sos_ui32_t cache_disabled :1; /* 1=cache disabled */
   sos_ui32_t zero2          :7; /* Intel reserved */
   sos_ui32_t pd_paddr       :20;
 } __attribute__ ((packed));
 
 
 /**
  * Helper macro to control the MMU: invalidate the TLB entry for the
  * page located at the given virtual address. See Intel x86 vol 3
  * section 3.7.
  */
 #define invlpg(vaddr) \
   do { \
        __asm__ __volatile__("invlpg %0"::"m"(*((unsigned *)(vaddr)))); \
   } while(0)
 
 
 /**
  * Helper macro to control the MMU: invalidate the whole TLB. See
  * Intel x86 vol 3 section 3.7.
  */
 #define flush_tlb() \
   do { \
         unsigned long tmpreg; \
         asm volatile("movl %%cr3,%0\n\tmovl %0,%%cr3" :"=r" \
                      (tmpreg) : :"memory"); \
   } while (0)
 
 
 /**
  * Helper macro to compute the index in the PD for the given virtual
  * address
  */
 #define virt_to_pd_index(vaddr) \
   (((unsigned)(vaddr)) >> 22)
 
 
 /**
  * Helper macro to compute the index in the PT for the given virtual
  * address
  */
 #define virt_to_pt_index(vaddr) \
   ( (((unsigned)(vaddr)) >> 12) & 0x3ff )
 
 
 /**
  * Helper macro to compute the offset in the page for the given virtual
  * address
  */
 #define virt_to_page_offset(vaddr) \
   (((unsigned)(vaddr)) & SOS_PAGE_MASK)
 
 
 /**
  * Helper function to map a page in the pd.\ Suppose that the RAM
  * is identity mapped to resolve PT actual (CPU) address from the PD
  * entry
  */
 static sos_ret_t paging_setup_map_helper(struct x86_pde * pd,
                                          sos_paddr_t ppage,
                                          sos_vaddr_t vaddr)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
 
   /* Make sure the page table was mapped */
   struct x86_pte * pt;
   if (pd[index_in_pd].present)
     {
       pt = (struct x86_pte*) (pd[index_in_pd].pt_paddr << 12);
 
       /* This test will always be TRUE here, since the setup routine
          scans the kernel pages in a strictly increasing order: at
          each step, the map will result in the allocation of a new PT
          entry. For the sake of clarity, we keep the test here. */
       if (pt[index_in_pt].present)
         SOS_ASSERT_FATAL(FALSE); /* indicate a fatal error */
     }
   else
     {
       /* No : allocate a new one */
       pt = (struct x86_pte*) sos_physmem_ref_physpage_new(FALSE);
       if (! pt)
         return -SOS_ENOMEM;
       
       memset((void*)pt, 0x0, SOS_PAGE_SIZE);
 
       pd[index_in_pd].present  = TRUE;
       pd[index_in_pd].write    = 1; /* It would be too complicated to
                                        determine whether it
                                        corresponds to a real R/W area
                                        of the kernel code/data or
                                        read-only */
       pd[index_in_pd].pt_paddr = ((sos_paddr_t)pt) >> 12;
     }
 
   
   /* Map the page in the page table */
   pt[index_in_pt].present = 1;
   pt[index_in_pt].write   = 1;  /* It would be too complicated to
                                    determine whether it corresponds to
                                    a real R/W area of the kernel
                                    code/data or R/O only */
   pt[index_in_pt].user    = 0;
   pt[index_in_pt].paddr   = ppage >> 12;
 
   /* Increase the PT's occupation count because we allocated a new PTE
      inside it */
   sos_physmem_inc_physpage_occupation((sos_paddr_t)pt);
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_subsystem_setup(sos_paddr_t identity_mapping_base,
                                      sos_paddr_t identity_mapping_top)
 {
   /* The PDBR we will setup below */
   struct x86_pdbr cr3;  
 
   /* Get the PD for the kernel */
   struct x86_pde * pd
     = (struct x86_pde*) sos_physmem_ref_physpage_new(FALSE);
 
   /* The iterator for scanning the kernel area */
   sos_paddr_t paddr;
 
   /* Reset the PD. For the moment, there is still an IM for the whole
      RAM, so that the paddr are also vaddr */
   memset((void*)pd,
          0x0,
          SOS_PAGE_SIZE);
 
   /* Identity-map the identity_mapping_* area */
   for (paddr = identity_mapping_base ;
        paddr < identity_mapping_top ;
        paddr += SOS_PAGE_SIZE)
     {
       if (paging_setup_map_helper(pd, paddr, paddr))
         return -SOS_ENOMEM;
     }
 
   /* Identity-map the PC-specific BIOS/Video area */
   for (paddr = BIOS_N_VIDEO_START ;
        paddr < BIOS_N_VIDEO_END ;
        paddr += SOS_PAGE_SIZE)
     {
       if (paging_setup_map_helper(pd, paddr, paddr))
         return -SOS_ENOMEM;
     }
 
   /* Ok, kernel is now identity mapped in the PD. We still have to set
      up the mirroring */
   pd[virt_to_pd_index(SOS_PAGING_MIRROR_VADDR)].present = TRUE;
   pd[virt_to_pd_index(SOS_PAGING_MIRROR_VADDR)].write = 1;
   pd[virt_to_pd_index(SOS_PAGING_MIRROR_VADDR)].user  = 0;
   pd[virt_to_pd_index(SOS_PAGING_MIRROR_VADDR)].pt_paddr 
     = ((sos_paddr_t)pd)>>12;
 
   /* We now just have to configure the MMU to use our PD. See Intel
      x86 doc vol 3, section 3.6.3 */
   memset(& cr3, 0x0, sizeof(struct x86_pdbr)); /* Reset the PDBR */
   cr3.pd_paddr = ((sos_paddr_t)pd) >> 12;
 
  /* Actual loading of the PDBR in the MMU: setup cr3 + bits 31[Paging
     Enabled] and 16[Write Protect] of cr0, see Intel x86 doc vol 3,
     sections 2.5, 3.6.1 and 4.11.3 + note table 4-2 */
   asm volatile ("movl %0,%%cr3\n\t"
                 "movl %%cr0,%%eax\n\t"
                 "orl $0x80010000, %%eax\n\t" /* bit 31 | bit 16 */
                 "movl %%eax,%%cr0\n\t"
                 "jmp 1f\n\t"
                 "1:\n\t"
                 "movl $2f, %%eax\n\t"
                 "jmp *%%eax\n\t"
                 "2:\n\t" ::"r"(cr3):"memory","eax");
 
   /*
    * Here, the only memory available is:
    * - The BIOS+video area
    * - the identity_mapping_base .. identity_mapping_top area
    * - the PD mirroring area (4M)
    * All accesses to other virtual addresses will generate a #PF
    */
 
   return SOS_OK;
 }
 
 
 /* Suppose that the current address is configured with the mirroring
  * enabled to access the PD and PT. */
 sos_ret_t sos_paging_map(sos_paddr_t ppage_paddr,
                          sos_vaddr_t vpage_vaddr,
                          sos_bool_t is_user_page,
                          sos_ui32_t flags)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vpage_vaddr);
   unsigned index_in_pt = virt_to_pt_index(vpage_vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(ppage_paddr));
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(vpage_vaddr));
 
   /* EXEC permission ignored on x86 */
   flags &= ~SOS_VM_MAP_PROT_EXEC;
 
   /* The mapping of anywhere in the PD mirroring is FORBIDDEN ;) */
   if ((vpage_vaddr >= SOS_PAGING_MIRROR_VADDR)
       && (vpage_vaddr < SOS_PAGING_MIRROR_VADDR + SOS_PAGING_MIRROR_SIZE))
     return -SOS_EINVAL;
 
   /* Map a page for the PT if necessary */
   if (! pd[index_in_pd].present)
     {
       x86_pde_val_t u;
       
       /* No : allocate a new one */
       sos_paddr_t pt_ppage
         = sos_physmem_ref_physpage_new(! (flags & SOS_VM_MAP_ATOMIC));
       if (! pt_ppage)
         {
           return -SOS_ENOMEM;
         }
 
       /* Prepare the value of the PDE */
       u.pde = (struct x86_pde){
         .present  = TRUE,
         .write    = 1,
         .pt_paddr = ((sos_paddr_t)pt_ppage) >> 12
       };
 
       /* Is it a PDE concerning the kernel space */
       if (vpage_vaddr < SOS_PAGING_MIRROR_VADDR)
         {
           /* Yes: So we need to update the PDE of ALL the mm_contexts
              in the system */
 
           /* First of all: this is a kernel PT */
           u.pde.user = 0;
 
           /* Now synchronize all the PD */
           SOS_ASSERT_FATAL(SOS_OK ==
                            sos_mm_context_synch_kernel_PDE(index_in_pd,
                                                            u.ui32));
         }
       else /* We should have written "else if (vpage_vaddr >=
               SOS_PAGING_BASE_USER_ADDRESS)" but this is not needed
               because the beginning of the function detects and
               rejects mapping requests inside the mirroring */
         {
           /* No: The request concerns the user space. So only the
              current MMU context is concerned */
 
           /* First of all: this is a user PT */
           u.pde.user = 1;
 
           /* Now update the current PD */
           pd[index_in_pd] = u.pde;
         }
       
       /*
        * The PT is now mapped in the PD mirroring
        */
 
       /* Invalidate TLB for the page we just added */
       invlpg(pt);
      
       /* Reset this new PT */
       memset((void*)pt, 0x0, SOS_PAGE_SIZE);
     }
 
   /* If we allocate a new entry in the PT, increase its occupation
      count. */
   if (! pt[index_in_pt].present)
     sos_physmem_inc_physpage_occupation(pd[index_in_pd].pt_paddr << 12);
   
   /* Otherwise, that means that a physical page is implicitely
      unmapped */
   else
     sos_physmem_unref_physpage(pt[index_in_pt].paddr << 12);
 
   /* Map the page in the page table */
   pt[index_in_pt].present = TRUE;
   pt[index_in_pt].write   = (flags & SOS_VM_MAP_PROT_WRITE)?1:0;
   pt[index_in_pt].user    = (is_user_page)?1:0;
   pt[index_in_pt].paddr   = ppage_paddr >> 12;
   sos_physmem_ref_physpage_at(ppage_paddr);
 
 
   /*
    * The page is now mapped in the current address space
    */
   
   /* Invalidate TLB for the page we just added */
   invlpg(vpage_vaddr);
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_unmap(sos_vaddr_t vpage_vaddr)
 {
   sos_ret_t pt_dec_occupation_retval;
 
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vpage_vaddr);
   unsigned index_in_pt = virt_to_pt_index(vpage_vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(vpage_vaddr));
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return -SOS_EINVAL;
   if (! pt[index_in_pt].present)
     return -SOS_EINVAL;
 
   /* The unmapping of anywhere in the PD mirroring is FORBIDDEN ;) */
   if ((vpage_vaddr >= SOS_PAGING_MIRROR_VADDR)
       && (vpage_vaddr < SOS_PAGING_MIRROR_VADDR + SOS_PAGING_MIRROR_SIZE))
     return -SOS_EINVAL;
 
   /* Reclaim the physical page */
   sos_physmem_unref_physpage(pt[index_in_pt].paddr << 12);
 
   /* Unmap the page in the page table */
   memset(pt + index_in_pt, 0x0, sizeof(struct x86_pte));
 
   /* Invalidate TLB for the page we just unmapped */
   invlpg(vpage_vaddr);
 
   /* Reclaim this entry in the PT, which may free the PT */
   pt_dec_occupation_retval
     = sos_physmem_dec_physpage_occupation(pd[index_in_pd].pt_paddr << 12);
   SOS_ASSERT_FATAL(pt_dec_occupation_retval >= 0);
   if (pt_dec_occupation_retval > 0)
     /* If the PT is now completely unused... */
     {
       x86_pde_val_t u;
 
 
       /*
        * The PT is not referenced by this PD anymore
        */
       sos_physmem_unref_physpage(pd[index_in_pd].pt_paddr << 12);
 
 
       /*
        * Reset the PDE
        */
 
       /* Mark the PDE as unavailable */
       u.ui32 = 0;
 
       /* Is it a PDE concerning the kernel space */
       if (vpage_vaddr < SOS_PAGING_MIRROR_VADDR)
         {
           /* Now synchronize all the PD */
           SOS_ASSERT_FATAL(SOS_OK ==
                            sos_mm_context_synch_kernel_PDE(index_in_pd,
                                                            u.ui32));
         }
       else /* We should have written "else if (vpage_vaddr >=
               SOS_PAGING_BASE_USER_ADDRESS)" but this is not needed
               because the beginning of the function detects and
               rejects mapping requests inside the mirroring */
         {
           /* No: The request concerns the user space. So only the
              current MMU context is concerned */
           pd[index_in_pd] = u.pde;
         }
       
       /* Update the TLB */
       invlpg(pt);
     }
 
   return SOS_OK;  
 }
 
 
 sos_ret_t sos_paging_unmap_interval(sos_vaddr_t vaddr,
                                     sos_size_t  size)
 {
   sos_ret_t retval = 0;
 
   if (! SOS_IS_PAGE_ALIGNED(vaddr))
     return -SOS_EINVAL;
   if (! SOS_IS_PAGE_ALIGNED(size))
     return -SOS_EINVAL;
 
   for ( ;
         size >= SOS_PAGE_SIZE ;
         vaddr += SOS_PAGE_SIZE, size -= SOS_PAGE_SIZE)
     if (SOS_OK == sos_paging_unmap(vaddr))
       retval += SOS_PAGE_SIZE;
 
   return retval;
 }
 
 
 sos_ui32_t sos_paging_get_prot(sos_vaddr_t vaddr)
 {
   sos_ui32_t retval;
 
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return SOS_VM_MAP_PROT_NONE;
   if (! pt[index_in_pt].present)
     return SOS_VM_MAP_PROT_NONE;
   
   /* Default access right of an available page is "read" on x86 */
   retval = SOS_VM_MAP_PROT_READ;
   if (pd[index_in_pd].write && pt[index_in_pt].write)
     retval |= SOS_VM_MAP_PROT_WRITE;
 
   return retval;
 }
 
 
 sos_ret_t sos_paging_set_prot(sos_vaddr_t vaddr,
                               sos_ui32_t  new_prot)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* EXEC permission ignored on x86 */
   new_prot &= ~SOS_VM_MAP_PROT_EXEC;
 
   /* Check flags */
   if (new_prot & ~(SOS_VM_MAP_PROT_READ | SOS_VM_MAP_PROT_WRITE))
     return -SOS_EINVAL;
   if (! (new_prot & SOS_VM_MAP_PROT_READ))
     /* x86 READ flag always set by default */
     return -SOS_ENOSUP;
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return -SOS_EINVAL;
   if (! pt[index_in_pt].present)
     return -SOS_EINVAL;
 
   /* Update access rights */
   pt[index_in_pt].write = ((new_prot & SOS_VM_MAP_PROT_WRITE) != 0);
   invlpg(vaddr);
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_set_prot_of_interval(sos_vaddr_t vaddr,
                                           sos_size_t  size,
                                           sos_ui32_t  new_prot)
 {
   if (! SOS_IS_PAGE_ALIGNED(vaddr))
     return -SOS_EINVAL;
   if (! SOS_IS_PAGE_ALIGNED(size))
     return -SOS_EINVAL;
 
   for ( ; size >= SOS_PAGE_SIZE ; vaddr += SOS_PAGE_SIZE, size -= SOS_PAGE_SIZE)
     sos_paging_set_prot(vaddr, new_prot);
 
   return SOS_OK;
 }
 
 
 sos_bool_t sos_paging_is_dirty(sos_vaddr_t vaddr)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return FALSE;
   if (! pt[index_in_pt].present)
     return FALSE;
 
   return (pt[index_in_pt].dirty != 0);
 }
 
 
 sos_ret_t sos_paging_set_dirty(sos_vaddr_t vaddr,
                                sos_bool_t is_dirty)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return -SOS_EFAULT;
   if (! pt[index_in_pt].present)
     return -SOS_EFAULT;
 
   pt[index_in_pt].dirty = is_dirty;
   return SOS_OK;
 }
 
 
 sos_paddr_t sos_paging_get_paddr(sos_vaddr_t vaddr)
 {
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(vaddr);
   unsigned index_in_pt = virt_to_pt_index(vaddr);
   unsigned offset_in_page = virt_to_page_offset(vaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return (sos_paddr_t)NULL;
   if (! pt[index_in_pt].present)
     return (sos_paddr_t)NULL;
 
   return (pt[index_in_pt].paddr << 12) + offset_in_page;
 }
 
 
 /* *************************************************
  * Functions restricted to mm_context module
  */
 
 
 sos_paddr_t sos_paging_get_current_PD_paddr(void)
 {
   struct x86_pdbr pdbr;
   asm volatile("movl %%cr3, %0\n": "=r"(pdbr));
   return (pdbr.pd_paddr << 12);
 }
 
 
 sos_ret_t sos_paging_set_current_PD_paddr(sos_paddr_t paddr_PD)
 {
   struct x86_pdbr pdbr;
 
   SOS_ASSERT_FATAL(paddr_PD != 0);
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(paddr_PD));
 
   /* Setup the value of the PDBR */
   memset(& pdbr, 0x0, sizeof(struct x86_pdbr)); /* Reset the PDBR */
   pdbr.pd_paddr = (paddr_PD >> 12);
 
   /* Configure the MMU according to the PDBR */
   asm volatile ("movl %0,%%cr3\n" ::"r"(pdbr));
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_dispose(sos_vaddr_t vaddr_PD)
 {
   x86_pde_val_t *pd = (x86_pde_val_t*) vaddr_PD;
   x86_pte_val_t *pt;
   int           index_in_pd;
 
   /* Allocate 1 page in kernel space to map the PTs in order to
      unreference the physical pages they reference */
   pt = (x86_pte_val_t *)sos_kmem_vmm_alloc(1, 0);
   if (! pt)
     return -SOS_ENOMEM;
 
   /* (Nothing to do in kernel space) */
 
   /* Reset all the PTs in user space */
   for (index_in_pd = (SOS_PAGING_BASE_USER_ADDRESS >> 22) ;
        index_in_pd < 1024 ; /* 1 PDE = 1 PT
                                = 1024 Pages
                                = 4MB */
        index_in_pd ++)
     {
       sos_paddr_t paddr_pt = (pd[index_in_pd].pde.pt_paddr << 12);
       int index_in_pt;
 
       /* Nothing to do if there is no PT */
       if (! pd[index_in_pd].pde.present)
         {
           pd[index_in_pd].ui32 = 0;
           continue;
         }
 
       /* Map this PT inside kernel */
       SOS_ASSERT_FATAL(SOS_OK
                        == sos_paging_map(paddr_pt,
                                          (sos_vaddr_t)pt, FALSE,
                                          SOS_VM_MAP_PROT_READ
                                          | SOS_VM_MAP_PROT_WRITE));
       
       /* Reset all the mappings in this PT */
       for (index_in_pt = 0 ; index_in_pt < 1024 ; index_in_pt ++)
         {
           /* Ignore unmapped PTE */
           if (! pt[index_in_pt].pte.present)
             {
               pt[index_in_pt].ui32 = 0;
               continue;
             }
 
           /* Unreference the associated page */
           sos_physmem_unref_physpage(pt[index_in_pt].pte.paddr << 12);
 
           /* Decrease occupation count of the PT */
           sos_physmem_dec_physpage_occupation(paddr_pt);
 
           /* Reset PTE */
           pt[index_in_pt].ui32 = 0;
         }
 
       /* Unmap PT */
       SOS_ASSERT_FATAL(SOS_OK == sos_paging_unmap((sos_vaddr_t)pt));
 
       /* Reset PDE */
       pd[index_in_pd].ui32 = 0;
 
       /* Unreference PT */
       sos_physmem_unref_physpage(paddr_pt);
     }
 
   /* Unallocate kernel space used for the temporary PT */
   SOS_ASSERT_FATAL(SOS_OK == sos_kmem_vmm_free((sos_vaddr_t)pt));
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_copy_kernel_space(sos_vaddr_t dest_vaddr_PD,
                                        sos_vaddr_t src_vaddr_PD)
 {
   x86_pde_val_t *src_pd       = (x86_pde_val_t*) src_vaddr_PD;
   x86_pde_val_t *dest_pd      = (x86_pde_val_t*) dest_vaddr_PD;
   sos_paddr_t   dest_paddr_PD = sos_paging_get_paddr(dest_vaddr_PD);
   x86_pde_val_t mirror_pde;
   int           index_in_pd;
 
   /* Fill destination PD with zeros */
   memset((void*)dest_vaddr_PD, 0x0, SOS_PAGE_SIZE);
 
   /* Synchronize it with the master Kernel MMU context. Stop just
      before the mirroring ! */
   for (index_in_pd = 0 ;
        index_in_pd < (SOS_PAGING_MIRROR_VADDR >> 22) ; /* 1 PDE = 1 PT
                                                           = 1024 Pages
                                                           = 4MB */
        index_in_pd ++)
     {
       /* Copy the master's configuration */
       dest_pd[index_in_pd].ui32 = src_pd[index_in_pd].ui32;
 
       /* We DON'T mark the underlying PT and pages as referenced
          because all the PD are equivalent in the kernel space: as
          soon as a page is mapped in the kernel, it is mapped by X
          address spaces, and as soon as it is unmapped by 1 address
          space, it is unmapped in all the others. So that for X
          address spaces, the reference counter will be either 0 or X,
          and not something else: using the reference counter correctly
          won't be of any use and would consume some time in updating it. */
     }
 
   /* Setup the mirroring for the new address space */
   mirror_pde.ui32 = 0;
   mirror_pde.pde.present  = TRUE;
   mirror_pde.pde.write    = 1;
   mirror_pde.pde.user     = 0; /* This is a KERNEL PDE */
   mirror_pde.pde.pt_paddr = (dest_paddr_PD >> 12);
   dest_pd[SOS_PAGING_MIRROR_VADDR >> 22].ui32 = mirror_pde.ui32;
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_copy_user_space(sos_vaddr_t dest_vaddr_PD,
                                      sos_vaddr_t src_vaddr_PD)
 {
   x86_pde_val_t *src_pd  = (x86_pde_val_t*) src_vaddr_PD;
   x86_pde_val_t *dest_pd = (x86_pde_val_t*) dest_vaddr_PD;
   x86_pte_val_t *tmp_src_pt, *tmp_dest_pt;
   int           index_in_pd;
 
   /* Allocate 2 pages in kernel space to map the PT in order to
      perform the copy of the PTs from source to destination */
   tmp_src_pt  = (x86_pte_val_t *)sos_kmem_vmm_alloc(1, 0);
   if (! tmp_src_pt)
     return -SOS_ENOMEM;
 
   tmp_dest_pt = (x86_pte_val_t *)sos_kmem_vmm_alloc(1, 0);
   if (! tmp_dest_pt)
     {
       sos_kmem_vmm_free((sos_vaddr_t)tmp_dest_pt);
       return -SOS_ENOMEM;
     }
 
   /* Copy each used PT from source to destination */
   for (index_in_pd = (SOS_PAGING_BASE_USER_ADDRESS >> 22) ;
        index_in_pd < 1024 ; /* 1 PDE = 1 PT
                                = 1024 Pages
                                = 4MB */
        index_in_pd ++)
     {
       sos_paddr_t paddr_dest_pt;
       int         index_in_pt;
 
       /* We first litterally copy the source PDE in the destination
          PDE. However, please bare in mind that, in the end, both
          won't reference the same physical PT: the destination PDE
          will be updated (below) to match the address of its own new
          PT */
       dest_pd[index_in_pd].ui32 = src_pd[index_in_pd].ui32;
 
       /* Ignore unused PTs */
       if (! src_pd[index_in_pd].pde.present)
         continue;
 
       /* Allocate the destination PT */
       paddr_dest_pt = sos_physmem_ref_physpage_new(TRUE);
       if (NULL == (void*)paddr_dest_pt)
         {
           sos_paging_dispose((sos_vaddr_t)dest_vaddr_PD);
           
           /* Unallocate temporary kernel space used for the copy */
           sos_kmem_vmm_free((sos_vaddr_t)tmp_src_pt);
           sos_kmem_vmm_free((sos_vaddr_t)tmp_dest_pt);
           return -SOS_ENOMEM;
         }
 
       /* Map source and destination PT */
       SOS_ASSERT_FATAL(SOS_OK
                        == sos_paging_map(src_pd[index_in_pd].pde.pt_paddr << 12,
                                          (sos_vaddr_t)tmp_src_pt, FALSE,
                                          SOS_VM_MAP_PROT_READ));
       SOS_ASSERT_FATAL(SOS_OK
                        == sos_paging_map(paddr_dest_pt,
                                          (sos_vaddr_t)tmp_dest_pt, FALSE,
                                          SOS_VM_MAP_PROT_READ
                                          | SOS_VM_MAP_PROT_WRITE));
 
       /* Copy the contents of the source to the destination PT,
          updating the reference counts of the pages */
       for (index_in_pt = 0 ; index_in_pt < 1024 ; index_in_pt ++)
         {
           /* Copy the source PTE */
           tmp_dest_pt[index_in_pt].ui32 = tmp_src_pt[index_in_pt].ui32;
           
           /* Ignore non-present pages */
           if (! tmp_dest_pt[index_in_pt].pte.present)
             continue;
 
           /* Reset the dirty/accessed flags */
           tmp_dest_pt[index_in_pt].pte.accessed = 0;
           tmp_dest_pt[index_in_pt].pte.dirty    = 0;
 
           /* Increase the reference count of the destination page */
           sos_physmem_ref_physpage_at(tmp_src_pt[index_in_pt].pte.paddr << 12);
 
           /* Increase occupation count of the PT */
           sos_physmem_inc_physpage_occupation(paddr_dest_pt);
         }
 
       /* Unmap the temporary PTs */
       SOS_ASSERT_FATAL(SOS_OK == sos_paging_unmap((sos_vaddr_t)tmp_src_pt));
       SOS_ASSERT_FATAL(SOS_OK == sos_paging_unmap((sos_vaddr_t)tmp_dest_pt));
 
       /* Update the destination PDE */
       dest_pd[index_in_pd].pde.pt_paddr = (paddr_dest_pt >> 12);
 
       /* Reset the dirty/accessed flags */
       dest_pd[index_in_pd].pde.accessed = 0;
     }
 
 
   /* Unallocate temporary kernel space used for the copy */
   SOS_ASSERT_FATAL(SOS_OK == sos_kmem_vmm_free((sos_vaddr_t)tmp_src_pt));
   SOS_ASSERT_FATAL(SOS_OK == sos_kmem_vmm_free((sos_vaddr_t)tmp_dest_pt));
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_prepare_COW(sos_uaddr_t base_address,
                                  sos_size_t length)
 {
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(base_address));
   SOS_ASSERT_FATAL(SOS_IS_PAGE_ALIGNED(length));
   SOS_ASSERT_FATAL(SOS_PAGING_BASE_USER_ADDRESS <= base_address);
 
   /* Mark all the pages read-only, when already mapped in physical
      memory */
   for ( ;
        length > 0 ;
        length -= SOS_PAGE_SIZE, base_address += SOS_PAGE_SIZE)
     {
       sos_paging_set_prot(base_address,
                           SOS_VM_MAP_PROT_READ);
     }
 
   return SOS_OK;
 }
 
 
 sos_ret_t sos_paging_try_resolve_COW(sos_uaddr_t uaddr)
 {
   sos_ret_t refcnt;
 
   /* Get the page directory entry and table entry index for this
      address */
   unsigned index_in_pd = virt_to_pd_index(uaddr);
   unsigned index_in_pt = virt_to_pt_index(uaddr);
   
   /* Get the PD of the current context */
   struct x86_pde *pd = (struct x86_pde*)
     (SOS_PAGING_MIRROR_VADDR
      + SOS_PAGE_SIZE*virt_to_pd_index(SOS_PAGING_MIRROR_VADDR));
 
   /* Address of the PT in the mirroring */
   struct x86_pte * pt = (struct x86_pte*) (SOS_PAGING_MIRROR_VADDR
                                            + SOS_PAGE_SIZE*index_in_pd);
 
   /* No page mapped at this address ? */
   if (! pd[index_in_pd].present)
     return -SOS_EFAULT;
   if (! pt[index_in_pt].present)
     return -SOS_EFAULT;
   
   /* Read-only PT not supported by kernel ! */
   if (! pd[index_in_pd].write)
     return -SOS_EFAULT;
 
   /* Cannot understand a COW request if the page is already
      read/write */
   SOS_ASSERT_FATAL(! pt[index_in_pt].write);
 
   /* We do a private copy of the page only if the current mapped page
      is shared by more than 1 process */
   refcnt = sos_physmem_get_physpage_refcount(pt[index_in_pt].paddr << 12);
   SOS_ASSERT_FATAL(refcnt > 0);
 
   if (refcnt == 1)
     {
       /* We are the only address space to reference this page, we can
          safely turn it read/write now */
       pt[index_in_pt].write = 1;
       invlpg(pt[index_in_pt].paddr << 12);
     }
 
   /* Otherwise we need to make a private copy of the page */
   else
     {
       sos_paddr_t new_ppage;
       sos_vaddr_t vpage_src, tmp_dest;
 
       /* For that, we allocate the destination page inside the kernel
          space to perform the copy. We will transfer it into its
          final user-space address later */
       tmp_dest = sos_kmem_vmm_alloc(1, SOS_KMEM_VMM_MAP);
       if (! tmp_dest)
         return -SOS_ENOMEM;
 
       /* copy the contents of the page */
       vpage_src = SOS_PAGE_ALIGN_INF(uaddr);
       memcpy((void*)tmp_dest, (void*)vpage_src, SOS_PAGE_SIZE);
 
       /* replace the original (read-only) mapping with a (read/write)
          mapping to the new page. This will automatically unreference
          the original page */
       new_ppage = sos_paging_get_paddr(tmp_dest);
       SOS_ASSERT_FATAL(new_ppage != (sos_vaddr_t)NULL);
       if (SOS_OK != sos_paging_map(new_ppage, vpage_src,
                                    TRUE,
                                    SOS_VM_MAP_PROT_READ
                                    | SOS_VM_MAP_PROT_WRITE))
         {
           sos_kmem_vmm_free(tmp_dest);
           return -SOS_ENOMEM;
         }
 
       /* We can now unmap the destination page from inside the
          kernel and free the kernel VM range for it */
       SOS_ASSERT_FATAL(SOS_OK == sos_kmem_vmm_free(tmp_dest));
     }
 
   /* That's all, folks ! */
   return SOS_OK;
 }