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Date: Fri, 26 Dec 2008 16:22:21 +0200
From: Avi Kivity <avi@...hat.com>
To: Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Cc: jeremy@...p.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH 1/4] x86: drop the use of the tss interrupt stack table (IST)
The IST is the only thing that requires a valid TSS while running in
kernel mode. Dropping its use unlocks an optimization opportunity for
kvm: if we don't need a valid TSS while in kernel mode we can defer the
use of the VMLOAD/VMSAVE instructions until the next context switch,
reducing the executions of these costly instructions by a nice factor.
Kernel reliability should also be improved since interrupt paths are
simplified.
Signed-off-by: Avi Kivity <avi@...hat.com>
---
arch/x86/include/asm/desc.h | 12 -----
arch/x86/include/asm/page_64.h | 7 ---
arch/x86/include/asm/processor.h | 11 ----
arch/x86/kernel/cpu/common.c | 34 -------------
arch/x86/kernel/dumpstack_64.c | 96 --------------------------------------
arch/x86/kernel/entry_64.S | 27 +---------
arch/x86/kernel/traps.c | 12 ++--
7 files changed, 9 insertions(+), 190 deletions(-)
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index dc27705..c8787ff 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -367,18 +367,6 @@ static inline void set_task_gate(unsigned int n, unsigned int gdt_entry)
_set_gate(n, GATE_TASK, (void *)0, 0, 0, (gdt_entry<<3));
}
-static inline void set_intr_gate_ist(int n, void *addr, unsigned ist)
-{
- BUG_ON((unsigned)n > 0xFF);
- _set_gate(n, GATE_INTERRUPT, addr, 0, ist, __KERNEL_CS);
-}
-
-static inline void set_system_intr_gate_ist(int n, void *addr, unsigned ist)
-{
- BUG_ON((unsigned)n > 0xFF);
- _set_gate(n, GATE_INTERRUPT, addr, 0x3, ist, __KERNEL_CS);
-}
-
#else
/*
* GET_DESC_BASE reads the descriptor base of the specified segment.
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index 5ebca29..7c89095 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -16,13 +16,6 @@
#define IRQSTACK_ORDER 2
#define IRQSTACKSIZE (PAGE_SIZE << IRQSTACK_ORDER)
-#define STACKFAULT_STACK 1
-#define DOUBLEFAULT_STACK 2
-#define NMI_STACK 3
-#define DEBUG_STACK 4
-#define MCE_STACK 5
-#define N_EXCEPTION_STACKS 5 /* hw limit: 7 */
-
#define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT)
#define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1))
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 091cd88..16d0cbe 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -277,13 +277,6 @@ struct tss_struct {
DECLARE_PER_CPU(struct tss_struct, init_tss);
-/*
- * Save the original ist values for checking stack pointers during debugging
- */
-struct orig_ist {
- unsigned long ist[7];
-};
-
#define MXCSR_DEFAULT 0x1f80
struct i387_fsave_struct {
@@ -376,10 +369,6 @@ union thread_xstate {
struct xsave_struct xsave;
};
-#ifdef CONFIG_X86_64
-DECLARE_PER_CPU(struct orig_ist, orig_ist);
-#endif
-
extern void print_cpu_info(struct cpuinfo_x86 *);
extern unsigned int xstate_size;
extern void free_thread_xstate(struct task_struct *);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 376b9f9..6808c3a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -907,9 +907,6 @@ void __cpuinit pda_init(int cpu)
}
}
-static char boot_exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ +
- DEBUG_STKSZ] __page_aligned_bss;
-
extern asmlinkage void ignore_sysret(void);
/* May not be marked __init: used by software suspend */
@@ -935,12 +932,6 @@ void syscall_init(void)
unsigned long kernel_eflags;
-/*
- * Copies of the original ist values from the tss are only accessed during
- * debugging, no special alignment required.
- */
-DEFINE_PER_CPU(struct orig_ist, orig_ist);
-
#else
/* Make sure %fs is initialized properly in idle threads */
@@ -964,17 +955,13 @@ void __cpuinit cpu_init(void)
{
int cpu = stack_smp_processor_id();
struct tss_struct *t = &per_cpu(init_tss, cpu);
- struct orig_ist *orig_ist = &per_cpu(orig_ist, cpu);
unsigned long v;
- char *estacks = NULL;
struct task_struct *me;
int i;
/* CPU 0 is initialised in head64.c */
if (cpu != 0)
pda_init(cpu);
- else
- estacks = boot_exception_stacks;
me = current;
@@ -1004,27 +991,6 @@ void __cpuinit cpu_init(void)
if (cpu != 0 && x2apic)
enable_x2apic();
- /*
- * set up and load the per-CPU TSS
- */
- if (!orig_ist->ist[0]) {
- static const unsigned int order[N_EXCEPTION_STACKS] = {
- [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STACK_ORDER,
- [DEBUG_STACK - 1] = DEBUG_STACK_ORDER
- };
- for (v = 0; v < N_EXCEPTION_STACKS; v++) {
- if (cpu) {
- estacks = (char *)__get_free_pages(GFP_ATOMIC, order[v]);
- if (!estacks)
- panic("Cannot allocate exception "
- "stack %ld %d\n", v, cpu);
- }
- estacks += PAGE_SIZE << order[v];
- orig_ist->ist[v] = t->x86_tss.ist[v] =
- (unsigned long)estacks;
- }
- }
-
t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
/*
* <= is required because the CPU will access up to
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index c302d07..21a576b 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -19,81 +19,6 @@
#include "dumpstack.h"
-static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
- unsigned *usedp, char **idp)
-{
- static char ids[][8] = {
- [DEBUG_STACK - 1] = "#DB",
- [NMI_STACK - 1] = "NMI",
- [DOUBLEFAULT_STACK - 1] = "#DF",
- [STACKFAULT_STACK - 1] = "#SS",
- [MCE_STACK - 1] = "#MC",
-#if DEBUG_STKSZ > EXCEPTION_STKSZ
- [N_EXCEPTION_STACKS ...
- N_EXCEPTION_STACKS + DEBUG_STKSZ / EXCEPTION_STKSZ - 2] = "#DB[?]"
-#endif
- };
- unsigned k;
-
- /*
- * Iterate over all exception stacks, and figure out whether
- * 'stack' is in one of them:
- */
- for (k = 0; k < N_EXCEPTION_STACKS; k++) {
- unsigned long end = per_cpu(orig_ist, cpu).ist[k];
- /*
- * Is 'stack' above this exception frame's end?
- * If yes then skip to the next frame.
- */
- if (stack >= end)
- continue;
- /*
- * Is 'stack' above this exception frame's start address?
- * If yes then we found the right frame.
- */
- if (stack >= end - EXCEPTION_STKSZ) {
- /*
- * Make sure we only iterate through an exception
- * stack once. If it comes up for the second time
- * then there's something wrong going on - just
- * break out and return NULL:
- */
- if (*usedp & (1U << k))
- break;
- *usedp |= 1U << k;
- *idp = ids[k];
- return (unsigned long *)end;
- }
- /*
- * If this is a debug stack, and if it has a larger size than
- * the usual exception stacks, then 'stack' might still
- * be within the lower portion of the debug stack:
- */
-#if DEBUG_STKSZ > EXCEPTION_STKSZ
- if (k == DEBUG_STACK - 1 && stack >= end - DEBUG_STKSZ) {
- unsigned j = N_EXCEPTION_STACKS - 1;
-
- /*
- * Black magic. A large debug stack is composed of
- * multiple exception stack entries, which we
- * iterate through now. Dont look:
- */
- do {
- ++j;
- end -= EXCEPTION_STKSZ;
- ids[j][4] = '1' + (j - N_EXCEPTION_STACKS);
- } while (stack < end - EXCEPTION_STKSZ);
- if (*usedp & (1U << j))
- break;
- *usedp |= 1U << j;
- *idp = ids[j];
- return (unsigned long *)end;
- }
-#endif
- }
- return NULL;
-}
-
/*
* x86-64 can have up to three kernel stacks:
* process stack
@@ -107,7 +32,6 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
{
const unsigned cpu = get_cpu();
unsigned long *irqstack_end = (unsigned long *)cpu_pda(cpu)->irqstackptr;
- unsigned used = 0;
struct thread_info *tinfo;
int graph = 0;
@@ -140,26 +64,6 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
*/
tinfo = task_thread_info(task);
for (;;) {
- char *id;
- unsigned long *estack_end;
- estack_end = in_exception_stack(cpu, (unsigned long)stack,
- &used, &id);
-
- if (estack_end) {
- if (ops->stack(data, id) < 0)
- break;
-
- bp = print_context_stack(tinfo, stack, bp, ops,
- data, estack_end, &graph);
- ops->stack(data, "<EOE>");
- /*
- * We link to the next stack via the
- * second-to-last pointer (index -2 to end) in the
- * exception stack:
- */
- stack = (unsigned long *) estack_end[-2];
- continue;
- }
if (irqstack_end) {
unsigned long *irqstack;
irqstack = irqstack_end -
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1954a96..4d47cb8 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1066,26 +1066,6 @@ ENTRY(\sym)
END(\sym)
.endm
-.macro paranoidzeroentry_ist sym do_sym ist
-ENTRY(\sym)
- INTR_FRAME
- PARAVIRT_ADJUST_EXCEPTION_FRAME
- pushq $-1 /* ORIG_RAX: no syscall to restart */
- CFI_ADJUST_CFA_OFFSET 8
- subq $15*8, %rsp
- call save_paranoid
- TRACE_IRQS_OFF
- movq %rsp,%rdi /* pt_regs pointer */
- xorl %esi,%esi /* no error code */
- movq %gs:pda_data_offset, %rbp
- subq $EXCEPTION_STKSZ, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)
- call \do_sym
- addq $EXCEPTION_STKSZ, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)
- jmp paranoid_exit /* %ebx: no swapgs flag */
- CFI_ENDPROC
-END(\sym)
-.endm
-
.macro errorentry sym do_sym
ENTRY(\sym)
XCPT_FRAME
@@ -1380,8 +1360,8 @@ END(xen_failsafe_callback)
*/
.pushsection .kprobes.text, "ax"
-paranoidzeroentry_ist debug do_debug DEBUG_STACK
-paranoidzeroentry_ist int3 do_int3 DEBUG_STACK
+paranoidzeroentry debug do_debug
+paranoidzeroentry int3 do_int3
paranoiderrorentry stack_segment do_stack_segment
errorentry general_protection do_general_protection
errorentry page_fault do_page_fault
@@ -1390,7 +1370,7 @@ paranoidzeroentry machine_check do_machine_check
#endif
/*
- * "Paranoid" exit path from exception stack.
+ * "Paranoid" exit path
* Paranoid because this is used by NMIs and cannot take
* any kernel state for granted.
* We don't do kernel preemption checks here, because only
@@ -1521,7 +1501,6 @@ ENTRY(error_exit)
END(error_exit)
- /* runs on exception stack */
ENTRY(nmi)
INTR_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 18f056a..2b13f5c 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -962,10 +962,10 @@ void __init trap_init(void)
#endif
set_intr_gate(0, ÷_error);
- set_intr_gate_ist(1, &debug, DEBUG_STACK);
- set_intr_gate_ist(2, &nmi, NMI_STACK);
+ set_intr_gate(1, &debug);
+ set_intr_gate(2, &nmi);
/* int3 can be called from all */
- set_system_intr_gate_ist(3, &int3, DEBUG_STACK);
+ set_system_intr_gate(3, &int3);
/* int4 can be called from all */
set_system_intr_gate(4, &overflow);
set_intr_gate(5, &bounds);
@@ -974,19 +974,19 @@ void __init trap_init(void)
#ifdef CONFIG_X86_32
set_task_gate(8, GDT_ENTRY_DOUBLEFAULT_TSS);
#else
- set_intr_gate_ist(8, &double_fault, DOUBLEFAULT_STACK);
+ set_intr_gate(8, &double_fault);
#endif
set_intr_gate(9, &coprocessor_segment_overrun);
set_intr_gate(10, &invalid_TSS);
set_intr_gate(11, &segment_not_present);
- set_intr_gate_ist(12, &stack_segment, STACKFAULT_STACK);
+ set_intr_gate(12, &stack_segment);
set_intr_gate(13, &general_protection);
set_intr_gate(14, &page_fault);
set_intr_gate(15, &spurious_interrupt_bug);
set_intr_gate(16, &coprocessor_error);
set_intr_gate(17, &alignment_check);
#ifdef CONFIG_X86_MCE
- set_intr_gate_ist(18, &machine_check, MCE_STACK);
+ set_intr_gate(18, &machine_check);
#endif
set_intr_gate(19, &simd_coprocessor_error);
--
1.6.0.6
--
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