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Fixed utcb updating issue that was a significant burden.

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Any thread that touches a utcb inside the kernel now properly checks
whether the utcb is mapped on its owner, and whether the mapped physical
address matches that of the current thread's tables. If not the tables
are updated.

This way, even though page tables become incoherent on utcb address
change situations (such as fork() exit(), execve()) they get updated
as they are referenced.

Since mappings are added only conditionally, caches are flushed only
when an update is necessary.
This commit is contained in:
Bahadir Balban
2009-10-09 16:45:10 +03:00
parent a8a4b5ce6c
commit d39ffc6acd
6 changed files with 83 additions and 12 deletions
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50
src/generic/tcb.c
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@@ -1,7 +1,7 @@
/*
* Some ktcb related data
*
* Copyright (C) 2007 Bahadir Balban
* Copyright (C) 2007 - 2009 Bahadir Balban
*/
#include <l4/generic/tcb.h>
#include <l4/generic/space.h>
@@ -179,6 +179,53 @@ int tcb_check_and_lazy_map_utcb(struct ktcb *task)
BUG_ON(!task->utcb_address);
/*
* There you go:
*
* if task == current && not mapped, page-in, if not return -EFAULT
* if task != current && not mapped, page-in to task, return -EFAULT
* if task != current && task mapped, but mapped != current mapped, map it, return 0
* if task != current && task mapped, but mapped == current mapped, return 0
*/
if (current == task) {
/* Check own utcb, if not there, page it in */
if ((ret = check_access(task->utcb_address, UTCB_SIZE,
MAP_SVC_RW_FLAGS, 1)) < 0)
return -EFAULT;
else
return 0;
} else {
/* Check another's utcb, but don't try to map in */
if ((ret = check_access_task(task->utcb_address,
UTCB_SIZE,
MAP_SVC_RW_FLAGS, 0,
task)) < 0) {
return -EFAULT;
} else {
/*
* Task has it mapped, map it to self
* unless they're identical
*/
if ((phys =
virt_to_phys_by_pgd(task->utcb_address,
TASK_PGD(task))) !=
virt_to_phys_by_pgd(task->utcb_address,
TASK_PGD(current)))
/*
* We have none or an old reference.
* Update it with privileged flags,
* so that only kernel can access.
*/
printk("%s: Caught old utcb mapping.\n", __FUNCTION__);
add_mapping_pgd(phys, task->utcb_address,
page_align_up(UTCB_SIZE),
MAP_SVC_RW_FLAGS,
TASK_PGD(current));
BUG_ON(!phys);
}
}
#if 0
/*
* FIXME:
*
@@ -209,6 +256,7 @@ int tcb_check_and_lazy_map_utcb(struct ktcb *task)
}
}
}
#endif
return 0;
}