value (KERN_SUCCESS or KERN_RESOURCE_SHORTAGE) indicating if it succeeded
or failed. Change the `wired' and `access_type' arguments to a single
`flags' argument, which includes the access type, and flags:
PMAP_WIRED the old `wired' boolean
PMAP_CANFAIL pmap_enter() is allowed to fail
If PMAP_CANFAIL is not specified, the pmap should behave as it always
has in the face of a drastic resource shortage: fall over dead.
Change the fault handler to deal with failure (which indicates resource
shortage) by unlocking everything, waiting for the pagedaemon to free
more memory, then retrying the fault.
pmap_change_wiring(...,FALSE) unless the map entry claims the address
is unwired. This fixes the following scenario, as described on
tech-kern@netbsd.org on Wed 6/16/1999 12:25:23:
- User mlock(2)'s a buffer, to guarantee it will never become
non-resident while he is using it.
- User then does physio to that buffer. Physio calls uvm_vslock()
to lock down the pages and ensure that page faults do not happen
while the I/O is in progress (possibly in interrupt context).
- Physio does the I/O.
- Physio calls uvm_vsunlock(). This calls uvm_fault_unwire().
>>> HERE IS WHERE THE PROBLEM OCCURS <<<
uvm_fault_unwire() calls pmap_change_wiring(..., FALSE),
which now gives the pmap free reign to recycle the mapping
information for that page, which is illegal; the mapping is
still wired (due to the mlock(2)), but now access of the
page could cause a non-protection page fault (disallowed).
NOTE: This could eventually lead to a panic when the user
subsequently munlock(2)'s the buffer and the mapping info
has been recycled for use by another mapping!
the map be at least read-locked to call this function. This requirement
will be taken advantage of in a future commit.
* Write a uvm_fault_unwire() wrapper which read-locks the map and calls
uvm_fault_unwire_locked().
* Update the comments describing the locking contraints of uvm_fault_wire()
and uvm_fault_unwire().
looking up a kernel address, check to see if the address is on this
"interrupt-safe" list. If so, return failure immediately. This prevents
a locking screw if a page fault is taken on an interrupt-safe map in or
out of interrupt context.
releasing any swap resources. if we don't do this, we can
end up with a clean, swap-backed page, which is illegal.
tracked down by Bill Sommerfeld, fixes PR 7578.
define a flag UVM_PGA_USERESERVE to allow non-kernel object
allocations to use pages from the reserve.
use the new flag for allocations in pmap modules.
memory access a mapping was caused by. This is passed through from uvm_fault()
and udv_fault(), and in most other cases is 0.
The pmap module may use this to preset R/M information. On MMUs which require
R/M emulation, the implementation may preset the bits and avoid taking another
fault. On MMUs which keep R/M information in hardware, the implementation may
preset its cached bits to speed up the next call to pmap_is_modified() or
pmap_is_referenced().
- break anon related functions out of uvm_amap.c and put them in their own
file (uvm_anon.c). includes break up uvm_anon_init into an amap and an
an anon init function
- ensure that only functions within the amap module access amap structure
fields (add macros to amap api as needed)
- simplify uvm_faultinfo in uvm_fault.h (parent map tracking no longer needed)
- adjust locking and lookup functions in uvm_fault_i.h to reflect the above
- replace ufi.rvaddr with ufi.orig_rvaddr in uvm_fault.c since rvaddr is
no longer needed.
- no need to worry about share map translations in uvm_fault(). simplify.
UVM was written by chuck cranor <chuck@maria.wustl.edu>, with some
minor portions derived from the old Mach code. i provided some help
getting swap and paging working, and other bug fixes/ideas. chuck
silvers <chuq@chuq.com> also provided some other fixes.
this is the UVM kernel code portion.
this will be KNF'd shortly. :-)
chs