+++ /dev/null
-Most of the text from Keith Owens, hacked by AK
-
-x86_64 page size (PAGE_SIZE) is 4K.
-
-Like all other architectures, x86_64 has a kernel stack for every
-active thread. These thread stacks are THREAD_SIZE (2*PAGE_SIZE) big.
-These stacks contain useful data as long as a thread is alive or a
-zombie. While the thread is in user space the kernel stack is empty
-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 are:
-
-* Interrupt stack. IRQSTACKSIZE
-
- Used for external hardware interrupts. If this is the first external
- hardware interrupt (i.e. not a nested hardware interrupt) then the
- kernel switches from the current task to the interrupt stack. Like
- the split thread and interrupt stacks on i386 (with CONFIG_4KSTACKS),
- this gives more room for kernel interrupt processing without having
- to increase the size of every per thread stack.
-
- The interrupt stack is also used when processing a softirq.
-
-Switching to the kernel interrupt stack is done by software based on a
-per CPU interrupt nest counter. This is needed because x86-64 "IST"
-hardware stacks cannot nest without races.
-
-x86_64 also has a feature which is not available on i386, the ability
-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.
-
-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.)
-
-Events with different IST codes (i.e. with different stacks) can be
-nested. For example, a debug interrupt can safely be interrupted by an
-NMI. arch/x86_64/kernel/entry.S::paranoidentry adjusts the stack
-pointers on entry to and exit from all IST events, in theory allowing
-IST events with the same code to be nested. However in most cases, the
-stack size allocated to an IST assumes no nesting for the same code.
-If that assumption is ever broken then the stacks will become corrupt.
-
-The currently assigned IST stacks are :-
-
-* STACKFAULT_STACK. EXCEPTION_STKSZ (PAGE_SIZE).
-
- Used for interrupt 12 - Stack Fault Exception (#SS).
-
- 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 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).
-
- Used for non-maskable interrupts (NMI).
-
- NMI can be delivered at any time, including when the kernel is in the
- middle of switching stacks. Using IST for NMI events avoids making
- assumptions about the previous state of the kernel stack.
-
-* DEBUG_STACK. DEBUG_STKSZ
-
- Used for hardware debug interrupts (interrupt 1) and for software
- debug interrupts (INT3).
-
- When debugging a kernel, debug interrupts (both hardware and
- software) can occur at any time. Using IST for these interrupts
- avoids making assumptions about the previous state of the kernel
- stack.
-
-* MCE_STACK. EXCEPTION_STKSZ (PAGE_SIZE).
-
- Used for interrupt 18 - Machine Check Exception (#MC).
-
- MCE can be delivered at any time, including when the kernel is in the
- middle of switching stacks. Using IST for MCE events avoids making
- assumptions about the previous state of the kernel stack.
-
-For more details see the Intel IA32 or AMD AMD64 architecture manuals.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff