at it, use the ANSI C generic pointer type for the second argument,
thus matching the documentation.
Remove the now extraneous (and now conflicting) function declarations
in various libc sources. Remove now unnecessary casts.
Reviewed by: bde
such that 'ispcvt' can build. Unforunately 'ispcvt' is needed in order for
/etc/rc.d/syscons to run. This fixes the bug where I could not get my
keymap effective at boot.
of doing a loop and taking two 32 bit passes at the runqueue bits. All
the 64 bit platforms should probably do this since there are 64 run queues.
Approved by: re (scottl)
used on amd64, and were actually totally broken. They had the wrong
calling conventions. I believe the i386 versions are going away too.
Approved by: re (scottl)
i386 version. The curthread special case in pcpu.h solves my complaint
about the verbose macro expansion in this case. Note that the i386
version still has some OBE comments, I didn't re-add them back again.
Approved by: re (scottl)
the compiler having to parse and optimize the PCPU_GET(curthread) so often.
__curthread() is an inline optimized version of PCPU_GET(curthread) that
knows that pc_curthread is at offset zero in the pcpu struct. Add a
CTASSERT() to catch any possible changes to this. This accounts for
just over a 1% wall clock speedup for total kernel compile/link time,
and 20% compile time speedup on some specific files depending on which
compile options are used.
Approved by: re (jhb)
- This is heavily derived from John Baldwin's apic/pci cleanup on i386.
- I have completely rewritten or drastically cleaned up some other parts.
(in particular, bootstrap)
- This is still a WIP. It seems that there are some highly bogus bioses
on nVidia nForce3-150 boards. I can't stress how broken these boards
are. I have a workaround in mind, but right now the Asus SK8N is broken.
The Gigabyte K8NPro (nVidia based) is also mind-numbingly hosed.
- Most of my testing has been with SCHED_ULE. SCHED_4BSD works.
- the apic and acpi components are 'standard'.
- If you have an nVidia nForce3-150 board, you are stuck with 'device
atpic' in addition, because they somehow managed to forget to connect the
8254 timer to the apic, even though its in the same silicon! ARGH!
This directly violates the ACPI spec.
physical mapping.
- Move the sf_buf API to its own header file; make struct sf_buf's
definition machine dependent. In this commit, we remove an
unnecessary field from struct sf_buf on the alpha, amd64, and ia64.
Ultimately, we may eliminate struct sf_buf on those architecures
except as an opaque pointer that references a vm page.
- Move the IPI and local APIC interrupt vectors up into the 0xf0 - 0xff
range. The pmap lazyfix IPI was reordered down next to the TLB
shootdowns to avoid conflicting with the spurious interrupt vector.
- Move the base of APIC interrupts up 16 so that the first 16 APIC
interrupts do not overlap the vectors used by the ATPIC.
- Remove bogus interrupt vector reservations for LINT[01].
- Now that 0xc0 - 0xef are available, use them for device interrupts.
This increases the number of APIC device interrupts to 191.
- Increase the system-wide number of global interrupts to 191 to catch up
to more APIC interrupts.
Requested by: peter (2)
vector stubs and into the C functions they call.
- Move disabling and EOIing of interrupt sources out of PIC driver entry
points and into intr_execute_handlers(). Intr_execute_handlers() only
disables a source for an interrupt if it is a stray interrupt or has
threaded handlers. Sources with fast handlers no longer disable (mask)
the source while executing the handlers.
- Move the setting of clkintr_pending into intr_execute_handlers() and set
the variable for any interrupt source with a vector of 0. (Should only
be true for IRQ 0.) This fixes clkintr_pending in the NO_MIXED_MODE
case.
- Implement lapic_eoi() and use it to implement ioapic_eoi_source().
- Rename atpic_sched_ithd() to atpic_handle_intr() since it is used to
handle all atpic interrupts and not just threaded ones.
Inspired by: peter's changes to amd64 in p4 (1)
Requested by: bde (2)
- The apic interrupt entry points have been rewritten so that each entry
point can serve 32 different vectors. When the entry is executed, it
uses one of the 32-bit ISR registers to determine which vector in its
assigned range was triggered. Thus, the apic code can support 159
different interrupt vectors with only 5 entry points.
- We now always to disable the local APIC to work around an errata in
certain PPros and then re-enable it again if we decide to use the APICs
to route interrupts.
- We no longer map IO APICs or local APICs using special page table
entries. Instead, we just use pmap_mapdev(). We also no longer
export the virtual address of the local APIC as a global symbol to
the rest of the system, but only in local_apic.c. To aid this, the
APIC ID of each CPU is exported as a per-CPU variable.
- Interrupt sources are provided for each intpin on each IO APIC.
Currently, each source is given a unique interrupt vector meaning that
PCI interrupts are not shared on most machines with an I/O APIC.
That mapping for interrupt sources to interrupt vectors is up to the
APIC enumerator driver however.
- We no longer probe to see if we need to use mixed mode to route IRQ 0,
instead we always use mixed mode to route IRQ 0 for now. This can be
disabled via the 'NO_MIXED_MODE' kernel option.
- The npx(4) driver now always probes to see if a built-in FPU is present
since this test can now be performed with the new APIC code. However,
an SMP kernel will panic if there is more than one CPU and a built-in
FPU is not found.
- PCI interrupts are now properly routed when using APICs to route
interrupts, so remove the hack to psuedo-route interrupts when the
intpin register was read.
- The apic.h header was moved to apicreg.h and a new apicvar.h header
that declares the APIs used by the new APIC code was added.
that provides methods via a PIC driver to do things like mask a source,
unmask a source, enable it when the first interrupt handler is added, etc.
The interrupt code provides a table of interrupt sources indexed by IRQ
numbers, or vectors. These vectors are what new-bus uses for its IRQ
resources and for bus_setup_intr()/bus_teardown_intr(). The interrupt
code then maps that vector a given interrupt source object. When an
interrupt comes in, the low-level interrupt code looks up the interrupt
source for the source that triggered the interrupt and hands it off to
this code to execute the appropriate handlers.
By having an interrupt source abstraction, this allows us to have different
types of interrupt source providers within the shared IRQ address space.
For example, IRQ 0 may map to pin 0 of the master 8259A PIC, IRQs 1
through 60 may map to pins on various I/O APICs, and IRQs 120 through
128 may map to MSI interrupts for various PCI devices.
setting. Make va_copy be an alias if __ISO_C_VISIBLE >= 1999.
Why? more than a few ports have an autoconf that looks for __va_copy
because it is available on glibc. It is critical that we use it if
at all possible on amd64. It generally isn't a problem for i386 and its
ilk because autoconf driven code tends to fall back to an assignment.
implement i386 compat numbers where it makes sense. This would save a
syscall translation layer. Yes, this breaks the abi slightly again, but
fortunately its just a recompile rather than tweaking the source. I will
be fixing the libc stubs while I'm here.
sigreturn() ABI and the signal context on the stack.
Make the trapframe (and its shadows in the ucontext and sigframe etc)
8 bytes larger in order to preserve 16 byte stack alignment for the
following C code calls. I could have done some padding after the
trapframe was saved, but some of the C code still expects an argument of
'struct trapframe'. Anyway, this gives me a spare field that can be used
to store things like 'partial trapframe' status or something else in
the future.
The runtime impact is fairly small, *except* for threaded apps and things
that decode contexts and the signal stack (eg: cvsup binary). Signal
delivery isn't too badly affected because the kernel generates the
sigframe that sigreturn uses after the handler has been called.
The size of mcontext_t and struct sigframe hasn't changed. Only
the last few fields (sc_eip etc) got moved a little and I eliminated
a spare field. mc_len/sc_len did change location though so the
sanity checks there will still trap it.
avoid problems with some Pentium 4 cpus and some older PPro/Pentium2
cpus. There are several problems, some documented in Intel errata.
This patch:
1) moves the kernel to the second page in the PSE case. There is an
errata that says that you Must Not point a 4MB page at physical
address zero on older cpus. We avoided bugs here due to sheer luck.
2) sets up PSE page tables right from the start in locore, rather than
trying to switch from 4K to 4M (or 2M) pages part way through the boot
sequence at the same time that we're messing with PG_G.
For some reason, the pmap work over the last 18 months seems to tickle
the problems, and the PAE infrastructure changes disturb the cpu
bugs even more.
A couple of people have reported a problem with APM bios calls during
boot. I'll work with people to get this resolved.
Obtained from: bmilekic
systems where the data/stack/etc limits are too big for a 32 bit process.
Move the 5 or so identical instances of ELF_RTLD_ADDR() into imgact_elf.c.
Supply an ia32_fixlimits function. Export the clip/default values to
sysctl under the compat.ia32 heirarchy.
Have mmap(0, ...) respect the current p->p_limits[RLIMIT_DATA].rlim_max
value rather than the sysctl tweakable variable. This allows mmap to
place mappings at sensible locations when limits have been reduced.
Have the imgact_elf.c ld-elf.so.1 placement algorithm use the same
method as mmap(0, ...) now does.
Note that we cannot remove all references to the sysctl tweakable
maxdsiz etc variables because /etc/login.conf specifies a datasize
of 'unlimited'. And that causes exec etc to fail since it can no
longer find space to mmap things.
32 bit binary stuff. 32 bit binaries do not like it much when the kernel
tries hard to put things above the 8GB mark.
I have a work-in-progress to fix this properly, but I didn't want to burn
anybody with this yet.
initialize a TSC timecounter until we know if it is broke or not.
XXX I think there is a bug in the i386 code here. init_TSC_tc() comes
after:
if (statclock_disable)
return;
ie: if you turn off the statclock interrupt, you dont get the TSC either.
prototypes of cpu_halt(), cpu_reset() and swi_vm() from md_var.h to
cpu.h. This affects db_command.c and kern_shutdown.c.
ia64: move all MD prototypes from cpu.h to md_var.h. This affects
madt.c, interrupt.c and mp_machdep.c. Remove is_physical_memory().
It's not used (vm_machdep.c).
alpha: the MD prototypes have been left in cpu.h with a comment
that they should be there. Moving them is left for later. It was
expected that the impact would be significant enough to be done in
a seperate commit.
powerpc: MD prototypes left in cpu.h. Comment added.
Suggested by: bde
Tested with: make universe (pc98 incomplete)
- Add a macro for the logical shift needed to extract an APIC ID from
either from the local APIC ICR Hi register or the APIC ID registers of
the local and IO APICs.
set in cpu_critical_fork_exit() anymore.
- As far as I can tell, cpu_thread_link() has never been used, not even
when it was originally added, so remove it.
memory in bus_dmamem_alloc(). This is possible now that
contigmalloc() supports the M_ZERO flag.
- Remove the locking of Giant around calls to contigmalloc() since
contigmalloc() now grabs Giant itself.
fields in the low 32 bits of the local APIC ICR register. Use this macro
in place of APIC_RESV2_MASK when masking off existing bits from the ICR
when writing to it to send an IPI.
Tested by: scottl
AMD64, gcc (and the ABI) expects the x87 unit to be running in 80/64
mode (not 64/53) so that it can use it for 'long double' operations. It
takes the expected precision differences into account when generating
code.
the SSE mxcsr register as well. Since gcc will intermix SSE2 and x87
FP code, the fpsetround() etc mode had better be the same.
There are hooks to enable these inlines to be instantiated inside libc
for non-gcc or C++ callers. (g++ doesn't like the inlines that tried
to extract an integer and convert it to an enum).
on the implied sign extension. The single unified VADDR() macro was
not able to avoid sign extending the VM_MAXUSER_ADDRESS/USRSTACK values.
Be explicit about UVADDR() (positive address space) and KVADDR()
(kernel negative address space) to make mistakes show up more
spectacularly.
Increase user VM space from 1/2TB (512GB) to 128TB.
Add two new arguments to bus_dma_tag_create(): lockfunc and lockfuncarg.
Lockfunc allows a driver to provide a function for managing its locking
semantics while using busdma. At the moment, this is used for the
asynchronous busdma_swi and callback mechanism. Two lockfunc implementations
are provided: busdma_lock_mutex() performs standard mutex operations on the
mutex that is specified from lockfuncarg. dftl_lock() is a panic
implementation and is defaulted to when NULL, NULL are passed to
bus_dma_tag_create(). The only time that NULL, NULL should ever be used is
when the driver ensures that bus_dmamap_load() will not be deferred.
Drivers that do not provide their own locking can pass
busdma_lock_mutex,&Giant args in order to preserve the former behaviour.
sparc64 and powerpc do not provide real busdma_swi functions, so this is
largely a noop on those platforms. The busdma_swi on is64 is not properly
locked yet, so warnings will be emitted on this platform when busdma
callback deferrals happen.
If anyone gets panics or warnings from dflt_lock() being called, please
let me know right away.
Reviewed by: tmm, gibbs
to the machine-independent parts of the VM. At the same time, this
introduces vm object locking for the non-i386 platforms.
Two details:
1. KSTACK_GUARD has been removed in favor of KSTACK_GUARD_PAGES. The
different machine-dependent implementations used various combinations
of KSTACK_GUARD and KSTACK_GUARD_PAGES. To disable guard page, set
KSTACK_GUARD_PAGES to 0.
2. Remove the (unnecessary) clearing of PG_ZERO in vm_thread_new. In
5.x, (but not 4.x,) PG_ZERO can only be set if VM_ALLOC_ZERO is passed
to vm_page_alloc() or vm_page_grab().
The current name is confusing, because it indicates to
the client that a bus_dmamap_sync() operation is not
necessary when the flag is specified, which is wrong.
The main purpose of this flag is to hint the underlying
architecture that DMA memory should be mapped in a coherent
way, but the architecture can ignore it. But if the
architecture does supports coherent mapping of memory, then
it makes bus_dmamap_sync() calls cheap.
This flag is the same as the one in NetBSD's Bus DMA.
Reviewed by: gibbs, scottl, des (implicitly)
Approved by: re@ (jhb)
disassembler has not been updated yet, and will do some very strange
things. It does tracebacks (without function arguments due to regparm
calling conventions) if -fno-omit-frame-pointer is used (to come later).
This achieves basic functionality.
Approved by: re (amd64/* blanket)
BUS_DMASYNC_ definitions remain as before. The does not change the ABI,
and reverts the API to be a bit more compatible and flexible. This has
survived a full 'make universe'.
Approved by: re (bmah)
systems. Of note:
- Implement a direct mapped region using 2MB pages. This eliminates the
need for temporary mappings when getting ptes. This supports up to
512GB of physical memory for now. This should be enough for a while.
- Implement a 4-tier page table system. Most of the infrastructure is
there for 128TB of userland virtual address space, but only 512GB is
presently enabled due to a mystery bug somewhere. The design of this
was heavily inspired by the alpha pmap.c.
- The kernel is moved into the negative address space(!).
- The kernel has 2GB of KVM available.
- Provide a uma memory allocator to use the direct map region to take
advantage of the 2MB TLBs.
- Fixed some assumptions in the bus_space macros about the ability
to fit virtual addresses in an 'int'.
Notable missing things:
- pmap_growkernel() should be able to grow to 512GB of KVM by expanding
downwards below kernbase. The kernel must be at the top 2GB of the
negative address space because of gcc code generation strategies.
- need to fix the >512GB user vm code.
Approved by: re (blanket)
- Fix visibilty test for LONG_BIT and WORD_BIT. `#if defined(__FOO_VISIBLE)'
is alays wrong because __FOO_VISIBLE is always defined (to 0 for
invisibility).
sys/<arch>/include/limits.h
sys/<arch>/include/_limits.h:
- Style fixes.
Submitted by: bde
Reviewed by: bsdmike
Approved by: re (scottl)
load_gs() calls into a single place that is less likely to go wrong.
Eliminate the per-process context switching of MSR_GSBASE, because it
should be constant for a single cpu. Instead, save/restore it during
the loading of the new %gs selector for the new process.
Approved by: re (amd64/* blanket)
stolen from the ia64/ia32 code (indeed there was a repocopy), but I've
redone the MD parts and added and fixed a few essential syscalls. It
is sufficient to run i386 binaries like /bin/ls, /usr/bin/id (dynamic)
and p4. The ia64 code has not implemented signal delivery, so I had
to do that.
Before you say it, yes, this does need to go in a common place. But
we're in a freeze at the moment and I didn't want to risk breaking ia64.
I will sort this out after the freeze so that the common code is in a
common place.
On the AMD64 side, this required adding segment selector context switch
support and some other support infrastructure. The %fs/%gs etc code
is hairy because loading %gs will clobber the kernel's current MSR_GSBASE
setting. The segment selectors are not used by the kernel, so they're only
changed at context switch time or when changing modes. This still needs
to be optimized.
Approved by: re (amd64/* blanket)
we do not have to run so long with interrupts disabled. This involved
creating tf_addr in the trapframe. Reorganize the trap stubs so that
they consistently reserve the stack space and initialize any missing
bits.
Approved by: re (amd64 stuff)
bus_dma MD code for AMD64. (And a trivial ifdef update in dev/kbd because
of this). More updates are needed here to take advantage of the 64 bit
instructions.
Approved by: re (blanket amd64/*)
value on entry and exit. This isn't as easy as it sounds because when
we recursively trap or interrupt, we have to avoid duplicating the
swapgs instruction or we end up back with the userland %gs. I implemented
this by testing TF_CS to see if we're coming from supervisor mode
already, and check for returning to supervisor. To avoid a race with
interrupts in the brief period after beginning executing the handler and
before the swapgs, convert all trap gates to interrupt gates, and reenable
interrupts immediately after the swapgs. I am not happy with this.
There are other possible ways to do this that should be investigated.
(eg: storing the GS.base MSR value in the trapframe)
Add some sysarch functions to let the userland code get to this.
Approved by: re (blanket amd64/*)
could use different versions of the math code depending on whether there
was real floating point hardware or math emulation. Since the fpu is
part of the core specification on amd64, there is no need for this here.
Approved by: re (blanket amd64/*)
should really be renamed to fpu.h and npx.c to fpu.c since its part of
the core architecture on amd64 systems, not an isa 'numeric processor
extension'.
Remove DBL_DIG, DBL_MIN, DBL_MAX and their FLT_ counterparts, they
were marked for deprecation ever since SUSv1 at least.
Only define ULLONG_MIN/MAX and LLONG_MAX if long long type is
supported.
Restore a lost comment in MI _limits.h file and remove it from
sys/limits.h where it does not belong.
that were added to sparc64 and later powerpc, really should have been in
the MI area. But changing that now with insufficient preperation will
just cause too much pain.
Move MD_FETCH() to the MI sys/linker.h file to avoid another two copies
of it.
a heavily stripped down FreeBSD/i386 (brutally stripped down actually) to
attempt to get a stable base to start from. There is a lot missing still.
Worth noting:
- The kernel runs at 1GB in order to cheat with the pmap code. pmap uses
a variation of the PAE code in order to avoid having to worry about 4
levels of page tables yet.
- It boots in 64 bit "long mode" with a tiny trampoline embedded in the
i386 loader. This simplifies locore.s greatly.
- There are still quite a few fragments of i386-specific code that have
not been translated yet, and some that I cheated and wrote dumb C
versions of (bcopy etc).
- It has both int 0x80 for syscalls (but using registers for argument
passing, as is native on the amd64 ABI), and the 'syscall' instruction
for syscalls. int 0x80 preserves all registers, 'syscall' does not.
- I have tried to minimize looking at the NetBSD code, except in a couple
of places (eg: to find which register they use to replace the trashed
%rcx register in the syscall instruction). As a result, there is not a
lot of similarity. I did look at NetBSD a few times while debugging to
get some ideas about what I might have done wrong in my first attempt.
Rename visible x86_64 references to amd64.
Kill MID_MACHINE, its a.out specific, the only platform that supports it
is i386. All of the other platforms should remove it too.
to get actual constant values. This is in preparation for machine/limits.h
retirement.
Discussed on: standards@
Submitted by: Craig Rodrigues <rodrigc@attbi.com> (*)
Modified by: kan
enum to an int and redefine the BUS_DMASYNC_* constants as
flags. This allows us to specify several operations in one
call to bus_dmamap_sync() as in NetBSD.
the top of the address space to be reclaimed. The problem is that with
the APTD gone the mapable kernel address space runs right to the end of
the 32 bit address space. As a max this is 0x100000000, which can't be
represented in 32 bits, so we have to use ptd entry n-1 and pte offset
n-1, instead of ptd entry n and pte offset 0. There's still 1 page we
can't use, but we gain just under 4 megs of kva (8 megs with PAE).
Sponsored by: DARPA, Network Associates Laboratories
to take care of the KAME IPv6 code which needs ovbcopy() because NetBSD's
bcopy() doesn't handle overlap like ours.
Remove all implementations of ovbcopy().
Previously, bzero was a function pointer on i386, to save a jmp to
bzero_vector. Get rid of this microoptimization as it only confuses
things, adds machine-dependent code to an MD header, and doesn't really
save all that much.
This commit does not add my pagezero() / pagecopy() code.
as it could be and can do with some more cleanup. Currently its under
options LAZY_SWITCH. What this does is avoid %cr3 reloads for short
context switches that do not involve another user process. ie: we can
take an interrupt, switch to a kthread and return to the user without
explicitly flushing the tlb. However, this isn't as exciting as it could
be, the interrupt overhead is still high and too much blocks on Giant
still. There are some debug sysctls, for stats and for an on/off switch.
The main problem with doing this has been "what if the process that you're
running on exits while we're borrowing its address space?" - in this case
we use an IPI to give it a kick when we're about to reclaim the pmap.
Its not compiled in unless you add the LAZY_SWITCH option. I want to fix a
few more things and get some more feedback before turning it on by default.
This is NOT a replacement for Bosko's lazy interrupt stuff. This was more
meant for the kthread case, while his was for interrupts. Mine helps a
little for interrupts, but his helps a lot more.
The stats are enabled with options SWTCH_OPTIM_STATS - this has been a
pseudo-option for years, I just added a bunch of stuff to it.
One non-trivial change was to select a new thread before calling
cpu_switch() in the first place. This allows us to catch the silly
case of doing a cpu_switch() to the current process. This happens
uncomfortably often. This simplifies a bit of the asm code in cpu_switch
(no longer have to call choosethread() in the middle). This has been
implemented on i386 and (thanks to jake) sparc64. The others will come
soon. This is actually seperate to the lazy switch stuff.
Glanced at by: jake, jhb
kernel opition 'options PAE'. This will only work with device drivers which
either use busdma, or are able to handle 64 bit physical addresses.
Thanks to Lanny Baron from FreeBSD Systems for the loan of a test machine
with 6 gigs of ram.
Sponsored by: DARPA, Network Associates Laboratories, FreeBSD Systems
accessing an alternate address space this causes 1 page table page at
a time to be mapped in, rather than using the recursive mapping technique
to map in an entire alternate address space. The recursive mapping
technique changes large portions of the address space and requires global
tlb flushes, which seem to cause problems when PAE is enabled. This will
also allow IPIs to be avoided when mapping in new page table pages using
the same technique as is used for pmap_copy_page and pmap_zero_page.
Sponsored by: DARPA, Network Associates Laboratories
This keeps the logical cpu's halted in the idle loop. By default
the logical cpu's are halted at startup. It is also possible to
halt any cpu in the idle loop now using machdep.hlt_cpus.
Examples of how to use this:
machdep.hlt_cpus=1 halt cpu0
machdep.hlt_cpus=2 halt cpu1
machdep.hlt_cpus=4 halt cpu2
machdep.hlt_cpus=3 halt cpu0,cpu1
Reviewed by: jhb, peter
where physical addresses larger than virtual addresses, such as i386s
with PAE.
- Use this to represent physical addresses in the MI vm system and in the
i386 pmap code. This also changes the paddr parameter to d_mmap_t.
- Fix printf formats to handle physical addresses >4G in the i386 memory
detection code, and due to kvtop returning vm_paddr_t instead of u_long.
Note that this is a name change only; vm_paddr_t is still the same as
vm_offset_t on all currently supported platforms.
Sponsored by: DARPA, Network Associates Laboratories
Discussed with: re, phk (cdevsw change)
4 bits. This reportedly fixes booting on the SW7500CW2. Much thanks to
the submitter for tracking this down!
Submitted by: Brian Buchanan <brian@ncircle.com>
Reviewed by: peter
MFC after: 3 days
are machine dependent because they are not required to update the tlb when
mappings are added or removed, and doing so is machine dependent.
In addition, an implementation may require that pages mapped with pmap_kenter
have a backing vm_page_t, which is not necessarily true of all physical
pages, and so may choose to pass the vm_page_t to pmap_kenter instead of the
physical address in order to make this requirement clear.
for testing and setting the current and alternate address spaces.
- Changed PTDpde and APTDpde to arrays to support multiple page directory
pages.
ponsored by: DARPA, Network Associates Laboratories
- Changed VM_MAXUSER_ADDRESS to be defined in terms of PTDPTDI. In order for
assumptions about the recursive page table map to work it must be the base
of the recursive map. Any pte offset that's not NPTEPG will break these
assumptions.
Sponsored by: DARPA, Network Associates Laboratories
