diff options
Diffstat (limited to 'Documentation/x86_64')
| -rw-r--r-- | Documentation/x86_64/boot-options.txt | 7 | ||||
| -rw-r--r-- | Documentation/x86_64/kernel-stacks | 99 |
2 files changed, 106 insertions, 0 deletions
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt index 6da24e7a56cb..4303e0c12476 100644 --- a/Documentation/x86_64/boot-options.txt +++ b/Documentation/x86_64/boot-options.txt @@ -245,6 +245,13 @@ Debugging 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 noreplacement Don't replace instructions with more appropriate ones diff --git a/Documentation/x86_64/kernel-stacks b/Documentation/x86_64/kernel-stacks new file mode 100644 index 000000000000..bddfddd466ab --- /dev/null +++ b/Documentation/x86_64/kernel-stacks @@ -0,0 +1,99 @@ +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 is + +* 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 an 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 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. + +* 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. |