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#include "vm/pagefault.h"
#include "errno.h"
#include "globals.h"
#include "mm/mm.h"
#include "mm/mman.h"
#include "mm/mobj.h"
#include "mm/pframe.h"
#include "mm/tlb.h"
#include "types.h"
#include "util/debug.h"
/*
* Respond to a user mode pagefault by setting up the desired page.
*
* vaddr - The virtual address that the user pagefaulted on
* cause - A combination of FAULT_ flags indicating the type of operation that
* caused the fault (see pagefault.h)
*
* Implementation details:
* 1) Find the vmarea that contains vaddr, if it exists.
* 2) Check the vmarea's protections (see the vmarea_t struct) against the 'cause' of
* the pagefault. For example, error out if the fault has cause write and we don't
* have write permission in the area. Keep in mind:
* a) You can assume that FAULT_USER is always specified.
* b) If neither FAULT_WRITE nor FAULT_EXEC is specified, you may assume the
* fault was due to an attempted read.
* 3) Obtain the corresponding pframe from the vmarea's mobj. Be careful about
* locking and error checking!
* 4) Finally, set up a call to pt_map to insert a new mapping into the
* appropriate pagetable:
* a) Use pt_virt_to_phys() to obtain the physical address of the actual
* data.
* b) You should not assume that vaddr is page-aligned, but you should
* provide a page-aligned address to the mapping.
* c) For pdflags, use PT_PRESENT | PT_WRITE | PT_USER.
* d) For ptflags, start with PT_PRESENT | PT_USER. Also supply PT_WRITE if
* the user can and wants to write to the page.
* 5) Flush the TLB.
*
* Tips:
* 1) This gets called by _pt_fault_handler() in mm/pagetable.c, which
* importantly checks that the fault did not occur in kernel mode. Think
* about why a kernel mode page fault would be bad in Weenix. Explore
* _pt_fault_handler() to get a sense of what's going on.
* 2) If you run into any errors, you should segfault by calling
* do_exit(EFAULT).
*/
void handle_pagefault(uintptr_t vaddr, uintptr_t cause)
{
dbg(DBG_VM, "vaddr = 0x%p (0x%p), cause = %lu\n", (void *)vaddr,
PAGE_ALIGN_DOWN(vaddr), cause);
// Check that the vaddr is valid
if (vaddr < USER_MEM_LOW ||vaddr > USER_MEM_HIGH)
{
do_exit(EFAULT);
}
// Lookup the vmarea for this address
size_t pn = ADDR_TO_PN(vaddr);
vmarea_t* vma = vmmap_lookup(curproc->p_vmmap, pn);
if (!vma)
{
do_exit(EFAULT);
}
// Error out if we don't have any permission in the area
if (vma->vma_prot == PROT_NONE)
{
do_exit(EFAULT);
}
// Check the vmarea's protections (see the vmarea_t struct) against the 'cause' of the pagefault
if ((cause & FAULT_WRITE) && !(vma->vma_prot & PROT_WRITE))
{
do_exit(EFAULT);
}
else if ((cause & FAULT_EXEC) && !(vma->vma_prot & PROT_EXEC))
{
do_exit(EFAULT);
}
else if (!(vma->vma_prot & PROT_READ))
{
do_exit(EFAULT);
}
// Obtain the corresponding pframe from the vmarea's mobj
pframe_t* pfp;
mobj_lock(vma->vma_obj);
long status = mobj_get_pframe(
vma->vma_obj,
pn - vma->vma_start + vma->vma_off,
(long) ((cause & FAULT_WRITE) ? 1 : 0),
&pfp
);
mobj_unlock(vma->vma_obj);
if (status < 0)
{
do_exit(EFAULT);
}
// Set up a call to pt_map to insert a new mapping into the appropriate pagetable
uintptr_t paddr = pt_virt_to_phys((uintptr_t) pfp->pf_addr);
pframe_release(&pfp);
uint32_t ptflags = PT_PRESENT | PT_USER;
if (cause & FAULT_WRITE)
{
ptflags |= PT_WRITE;
}
status = pt_map(
curproc->p_pml4,
paddr,
(uintptr_t) PAGE_ALIGN_DOWN(vaddr),
PT_PRESENT | PT_USER | PT_WRITE,
ptflags
);
if (status < 0)
{
do_exit(EFAULT);
}
// Flush the TLB
tlb_flush(vaddr);
}
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