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-rw-r--r--Documentation/x86_64/kernel-stacks26
1 files changed, 13 insertions, 13 deletions
diff --git a/Documentation/x86_64/kernel-stacks b/Documentation/x86_64/kernel-stacks
index bddfddd466ab..5ad65d51fb95 100644
--- a/Documentation/x86_64/kernel-stacks
+++ b/Documentation/x86_64/kernel-stacks
@@ -9,9 +9,9 @@ zombie. While the thread is in user space the kernel stack is empty
9except for the thread_info structure at the bottom. 9except for the thread_info structure at the bottom.
10 10
11In addition to the per thread stacks, there are specialized stacks 11In addition to the per thread stacks, there are specialized stacks
12associated with each cpu. These stacks are only used while the kernel 12associated with each CPU. These stacks are only used while the kernel
13is in control on that cpu, when a cpu returns to user space the 13is in control on that CPU; when a CPU returns to user space the
14specialized stacks contain no useful data. The main cpu stacks is 14specialized stacks contain no useful data. The main CPU stacks are:
15 15
16* Interrupt stack. IRQSTACKSIZE 16* Interrupt stack. IRQSTACKSIZE
17 17
@@ -32,17 +32,17 @@ x86_64 also has a feature which is not available on i386, the ability
32to automatically switch to a new stack for designated events such as 32to automatically switch to a new stack for designated events such as
33double fault or NMI, which makes it easier to handle these unusual 33double fault or NMI, which makes it easier to handle these unusual
34events on x86_64. This feature is called the Interrupt Stack Table 34events on x86_64. This feature is called the Interrupt Stack Table
35(IST). There can be up to 7 IST entries per cpu. The IST code is an 35(IST). There can be up to 7 IST entries per CPU. The IST code is an
36index into the Task State Segment (TSS), the IST entries in the TSS 36index into the Task State Segment (TSS). The IST entries in the TSS
37point to dedicated stacks, each stack can be a different size. 37point to dedicated stacks; each stack can be a different size.
38 38
39An IST is selected by an non-zero value in the IST field of an 39An IST is selected by a non-zero value in the IST field of an
40interrupt-gate descriptor. When an interrupt occurs and the hardware 40interrupt-gate descriptor. When an interrupt occurs and the hardware
41loads such a descriptor, the hardware automatically sets the new stack 41loads such a descriptor, the hardware automatically sets the new stack
42pointer based on the IST value, then invokes the interrupt handler. If 42pointer based on the IST value, then invokes the interrupt handler. If
43software wants to allow nested IST interrupts then the handler must 43software wants to allow nested IST interrupts then the handler must
44adjust the IST values on entry to and exit from the interrupt handler. 44adjust the IST values on entry to and exit from the interrupt handler.
45(this is occasionally done, e.g. for debug exceptions) 45(This is occasionally done, e.g. for debug exceptions.)
46 46
47Events with different IST codes (i.e. with different stacks) can be 47Events with different IST codes (i.e. with different stacks) can be
48nested. For example, a debug interrupt can safely be interrupted by an 48nested. For example, a debug interrupt can safely be interrupted by an
@@ -58,17 +58,17 @@ The currently assigned IST stacks are :-
58 58
59 Used for interrupt 12 - Stack Fault Exception (#SS). 59 Used for interrupt 12 - Stack Fault Exception (#SS).
60 60
61 This allows to recover from invalid stack segments. Rarely 61 This allows the CPU to recover from invalid stack segments. Rarely
62 happens. 62 happens.
63 63
64* DOUBLEFAULT_STACK. EXCEPTION_STKSZ (PAGE_SIZE). 64* DOUBLEFAULT_STACK. EXCEPTION_STKSZ (PAGE_SIZE).
65 65
66 Used for interrupt 8 - Double Fault Exception (#DF). 66 Used for interrupt 8 - Double Fault Exception (#DF).
67 67
68 Invoked when handling a exception causes another exception. Happens 68 Invoked when handling one exception causes another exception. Happens
69 when the kernel is very confused (e.g. kernel stack pointer corrupt) 69 when the kernel is very confused (e.g. kernel stack pointer corrupt).
70 Using a separate stack allows to recover from it well enough in many 70 Using a separate stack allows the kernel to recover from it well enough
71 cases to still output an oops. 71 in many cases to still output an oops.
72 72
73* NMI_STACK. EXCEPTION_STKSZ (PAGE_SIZE). 73* NMI_STACK. EXCEPTION_STKSZ (PAGE_SIZE).
74 74