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Page fault handling fix.

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Factored out mapping of the physical page as the final generic code
after all fault-specific handling is done.

Fixed the error that zero page didn't have an owner (devzero).

Fixed the error that struct dirent did not have the record length
field as u16 as expected by userspace.
This commit is contained in:
Bahadir Balban
2008-04-14 00:09:57 +01:00
parent 7f815dd2dd
commit d6d97876bb
6 changed files with 72 additions and 83 deletions
Download Patch File Download Diff File Expand all files Collapse all files

142
tasks/mm0/src/fault.c
View File

@@ -261,19 +261,19 @@ struct page *copy_page(struct page *orig)
* - Check refcounting of shadows, their references, page refs,
* reduces increases etc.
*
* This handles copy-on-write semantics in various situations.
* This handles copy-on-write semantics in various situations. Returns
* page struct for copy page availabe for mapping.
*
* 1) Copy-on-write of read-only files. (Creates r/w shadows/adds pages)
* 2) Copy-on-write of forked RO shadows (Creates r/w shadows/adds pages)
* 3) Copy-on-write of shm files. (Adds pages to r/w shm file from devzero).
*/
int copy_on_write(struct fault_data *fault)
struct page *copy_on_write(struct fault_data *fault)
{
struct vm_obj_link *vmo_link, *shadow_link, *copier_link;
struct vm_object *vmo, *shadow;
struct page *page, *new_page;
struct vm_area *vma = fault->vma;
unsigned int reason = fault->reason;
unsigned long file_offset = fault_to_file_offset(fault);
/* Get the first object, either original file or a shadow */
@@ -293,7 +293,7 @@ int copy_on_write(struct fault_data *fault)
*/
if (!(vmo_link->obj->flags & VM_WRITE)) {
if (!(shadow_link = vma_create_shadow()))
return -ENOMEM;
return PTR_ERR(-ENOMEM);
dprintf("%s: Created a shadow.\n", __TASKNAME__);
/* Initialise the shadow */
shadow = shadow_link->obj;
@@ -364,54 +364,62 @@ int copy_on_write(struct fault_data *fault)
insert_page_olist(new_page, new_page->owner);
new_page->owner->npages++;
/* Map the new page to faulty task */
l4_map((void *)page_to_phys(new_page),
(void *)page_align(fault->address), 1,
(reason & VM_READ) ? MAP_USR_RO_FLAGS : MAP_USR_RW_FLAGS,
fault->task->tid);
dprintf("%s: Mapped 0x%x as writable to tid %d.\n", __TASKNAME__,
page_align(fault->address), fault->task->tid);
vm_object_print(new_page->owner);
/* Shared faults don't have shadows so we don't look for collapses */
if (!(vma->flags & VMA_SHARED)) {
/* Shm faults don't have shadows so we're done here. */
if (vma->flags & VMA_SHARED)
return 0;
/*
* Finished handling the actual fault, now check for possible
* shadow collapses. Does the copier completely shadow the one
* underlying it?
*/
if (!(vmo_link = vma_next_link(&copier_link->list, &vma->vm_obj_list))) {
/* Copier must have an object under it */
printf("Copier must have had an object under it!\n");
BUG();
}
/* Compare whether page caches overlap */
if (vm_object_is_subset(copier_link->obj, vmo_link->obj)) {
/*
* They do overlap, so keep reference to object but
* drop and delete the vma link.
* Finished handling the actual fault, now check for possible
* shadow collapses. Does the copier completely shadow the one
* underlying it?
*/
vmo = vmo_link->obj;
vma_drop_link(copier_link, vmo_link);
vmo_link = 0;
if (!(vmo_link = vma_next_link(&copier_link->list,
&vma->vm_obj_list))) {
/* Copier must have an object under it */
printf("Copier must have had an object under it!\n");
BUG();
}
/* vm object reference down to one and object is mergeable? */
if ((vmo->refcnt == 1) &&
(vmo->flags != VM_OBJ_FILE))
vma_merge_link(vmo);
/* Compare whether page caches overlap */
if (vm_object_is_subset(copier_link->obj, vmo_link->obj)) {
/*
* They do overlap, so keep reference to object but
* drop and delete the vma link.
*/
vmo = vmo_link->obj;
vma_drop_link(copier_link, vmo_link);
vmo_link = 0;
/*
* vm object reference down to one
* and object is mergeable?
*/
if ((vmo->refcnt == 1) &&
(vmo->flags != VM_OBJ_FILE))
vma_merge_link(vmo);
}
}
return 0;
return new_page;
}
/*
* Handles the page fault, all entries here are assumed *legal* faults,
* i.e. do_page_fault() should have already checked for illegal accesses.
* Handles the page fault, all entries here are assumed *legal*
* faults, i.e. do_page_fault() should have already checked
* for illegal accesses.
*
* NOTE:
* Anon/Shared pages:
* First access from first process is COW. All subsequent RW
* accesses (which are attempts of *sharing*) simply map that
* page to faulting processes.
*
* Non-anon/shared pages:
* First access from first process simply writes to the pages
* of that file. All subsequent accesses by other processes
* do so as well.
*/
int __do_page_fault(struct fault_data *fault)
{
unsigned int reason = fault->reason;
@@ -446,39 +454,18 @@ int __do_page_fault(struct fault_data *fault)
}
}
BUG_ON(!page);
/* Map it to faulty task */
l4_map((void *)page_to_phys(page),
(void *)page_align(fault->address), 1,
(reason & VM_READ) ? MAP_USR_RO_FLAGS : MAP_USR_RW_FLAGS,
fault->task->tid);
/* Print about the action, if debug enabled */
dprintf("%s: Mapped 0x%x as readable to tid %d.\n", __TASKNAME__,
page_align(fault->address), fault->task->tid);
vm_object_print(vmo_link->obj);
}
/* Handle write */
if ((reason & VM_WRITE) && (pte_flags & VM_READ)) {
/* Copy-on-write. All private vmas are always COW */
if (vma_flags & VMA_PRIVATE)
copy_on_write(fault);
if (vma_flags & VMA_PRIVATE) {
BUG_ON(IS_ERR(page = copy_on_write(fault)));
/*
* This handles shared pages that are both anon and non-anon.
*
* Anon/Shared pages:
* First access from first process is COW. All subsequent RW
* accesses (which are attempts of *sharing*) simply map that
* page to faulting processes.
*
* Non-anon/shared pages:
* First access from first process simply writes to the pages
* of that file. All subsequent accesses by other processes
* do so as well.
*/
else if ((vma_flags & VMA_SHARED)) {
} else if ((vma_flags & VMA_SHARED)) {
file_offset = fault_to_file_offset(fault);
BUG_ON(!(vmo_link = vma_next_link(&vma->vm_obj_list,
&vma->vm_obj_list)));
@@ -493,10 +480,8 @@ int __do_page_fault(struct fault_data *fault)
* page, so its a bug.
*/
if (vma_flags & VMA_ANONYMOUS) {
copy_on_write(fault);
/* We're done. So return */
return 0;
BUG_ON(IS_ERR(page = copy_on_write(fault)));
goto out_success;
} else {
printf("%s: Could not obtain faulty "
"page from regular file.\n",
@@ -505,19 +490,20 @@ int __do_page_fault(struct fault_data *fault)
}
}
BUG_ON(!page);
/* Map it to faulty task */
l4_map((void *)page_to_phys(page),
(void *)page_align(fault->address), 1,
(reason & VM_READ) ? MAP_USR_RO_FLAGS : MAP_USR_RW_FLAGS,
fault->task->tid);
dprintf("%s: Mapped 0x%x as writable to tid %d.\n", __TASKNAME__,
page_align(fault->address), fault->task->tid);
vm_object_print(vmo_link->obj);
} else
BUG();
}
out_success:
/* Map the new page to faulty task */
l4_map((void *)page_to_phys(page),
(void *)page_align(fault->address), 1,
(reason & VM_READ) ? MAP_USR_RO_FLAGS : MAP_USR_RW_FLAGS,
fault->task->tid);
dprintf("%s: Mapped 0x%x as writable to tid %d.\n", __TASKNAME__,
page_align(fault->address), fault->task->tid);
vm_object_print(page->owner);
return 0;
}

5
tasks/mm0/src/pagers.c
View File

@@ -301,7 +301,6 @@ int init_devzero(void)
zvirt = l4_map_helper(zphys, 1);
memset(zvirt, 0, PAGE_SIZE);
l4_unmap_helper(zvirt, 1);
zpage->refcnt++;
/* Allocate and initialise devzero file */
devzero = vm_file_create();
@@ -312,6 +311,10 @@ int init_devzero(void)
devzero->vm_obj.pager = &devzero_pager;
devzero->vm_obj.flags = VM_OBJ_FILE;
/* Initialise zpage */
zpage->refcnt++;
zpage->owner = &devzero->vm_obj;
list_add(&devzero->vm_obj.list, &vm_object_list);
list_add(&devzero->list, &vm_file_list);
return 0;