[PATCH] x86-64: cleanup Doc/x86_64/ files

                       is 20.

    memaper[=<order>]  Allocate an own aperture over RAM with size 32MB<<order.

                       (default: order=1, i.e. 64MB)

    merge              Do scather-gather (SG) merging. Implies "force"

    merge              Do scatter-gather (SG) merging. Implies "force"

                       (experimental).

    nomerge            Don't do scather-gather (SG) merging.

    nomerge            Don't do scatter-gather (SG) merging.

    noaperture         Ask the IOMMU not to touch the aperture for AGP.

    forcesac           Force single-address cycle (SAC) mode for masks <40bits

                       (experimental).

		This will also cause panics on machine check exceptions.

		Useful together with panic=30 to trigger a reboot.

  kstack=N   Print that many words from the kernel stack in oops dumps.

  kstack=N	Print N words from the kernel stack in oops dumps.

  pagefaulttrace  Dump all page faults. Only useful for extreme debugging

		and will create a lot of output.

		newfallback: use new unwinder but fall back to old if it gets

			stuck (default)

  call_trace=[old|both|newfallback|new]

		old: use old inexact backtracer

		new: use new exact dwarf2 unwinder

 		both: print entries from both

		newfallback: use new unwinder but fall back to old if it gets

			stuck (default)

Misc

Miscellaneous

  noreplacement  Don't replace instructions with more appropriate ones

		 for the CPU. This may be useful on asymmetric MP systems

		 where some CPU have less capabilities than the others.

		 where some CPUs have less capabilities than others.

---------------------------------------------------

Linux/x86-64 supports CPU hotplug now. For various reasons Linux wants to

know in advance boot time the maximum number of CPUs that could be plugged

know in advance of boot time the maximum number of CPUs that could be plugged

into the system. ACPI 3.0 currently has no official way to supply

this information from the firmware to the operating system.

except for the thread_info structure at the bottom.

In addition to the per thread stacks, there are specialized stacks

associated with each cpu.  These stacks are only used while the kernel

is in control on that cpu, when a cpu returns to user space the

specialized stacks contain no useful data.  The main cpu stacks is

associated with each CPU.  These stacks are only used while the kernel

is in control on that CPU; when a CPU returns to user space the

specialized stacks contain no useful data.  The main CPU stacks are:

* Interrupt stack.  IRQSTACKSIZE

to automatically switch to a new stack for designated events such as

double fault or NMI, which makes it easier to handle these unusual

events on x86_64.  This feature is called the Interrupt Stack Table

(IST).  There can be up to 7 IST entries per cpu. The IST code is an

index into the Task State Segment (TSS), the IST entries in the TSS

point to dedicated stacks, each stack can be a different size.

(IST).  There can be up to 7 IST entries per CPU. The IST code is an

index into the Task State Segment (TSS). The IST entries in the TSS

point to dedicated stacks; each stack can be a different size.

An IST is selected by an non-zero value in the IST field of an

An IST is selected by a non-zero value in the IST field of an

interrupt-gate descriptor.  When an interrupt occurs and the hardware

loads such a descriptor, the hardware automatically sets the new stack

pointer based on the IST value, then invokes the interrupt handler.  If

software wants to allow nested IST interrupts then the handler must

adjust the IST values on entry to and exit from the interrupt handler.

(this is occasionally done, e.g. for debug exceptions)

(This is occasionally done, e.g. for debug exceptions.)

Events with different IST codes (i.e. with different stacks) can be

nested.  For example, a debug interrupt can safely be interrupted by an

  Used for interrupt 12 - Stack Fault Exception (#SS).

  This allows to recover from invalid stack segments. Rarely

  This allows the CPU to recover from invalid stack segments. Rarely

  happens.

* DOUBLEFAULT_STACK.  EXCEPTION_STKSZ (PAGE_SIZE).

  Used for interrupt 8 - Double Fault Exception (#DF).

  Invoked when handling a exception causes another exception. Happens

  when the kernel is very confused (e.g. kernel stack pointer corrupt)

  Using a separate stack allows to recover from it well enough in many

  cases to still output an oops.

  Invoked when handling one exception causes another exception. Happens

  when the kernel is very confused (e.g. kernel stack pointer corrupt).

  Using a separate stack allows the kernel to recover from it well enough

  in many cases to still output an oops.

* NMI_STACK.  EXCEPTION_STKSZ (PAGE_SIZE).

The direct mapping covers all memory in the system up to the highest

memory address (this means in some cases it can also include PCI memory

holes)

holes).

vmalloc space is lazily synchronized into the different PML4 pages of

the processes using the page fault handler, with init_level4_pgt as

reference.

Current X86-64 implementations only support 40 bit of address space,

Current X86-64 implementations only support 40 bits of address space,

but we support up to 46 bits. This expands into MBZ space in the page tables.

-Andi Kleen, Jul 2004