[tip: x86/entry] x86/entry: Remove debug IDT frobbing

tip-bot2 for Peter Zijlstra
2020-05-30T09:57:30Z

The following commit has been merged into the x86/entry branch of tip:

Commit-ID: 8449e768dcb85b4d8db51482d8c9260bb05ccabc
Gitweb: https://git.kernel.org/tip/8449e768dcb85b4d8db51482d8c9260bb05ccabc
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 29 May 2020 23:27:37 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sat, 30 May 2020 10:00:09 +02:00

x86/entry: Remove debug IDT frobbing

This is all unused now.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200529213321.245019500@infradead.org

---
arch/x86/include/asm/debugreg.h | 19 +------------------
arch/x86/include/asm/desc.h | 34 +--------------------------------
arch/x86/kernel/cpu/common.c | 17 +----------------
arch/x86/kernel/idt.c | 30 +----------------------------
arch/x86/kernel/traps.c | 9 +--------
5 files changed, 1 insertion(+), 108 deletions(-)

diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h
index 3e1c502..42fc35d 100644
--- a/arch/x86/include/asm/debugreg.h
+++ b/arch/x86/include/asm/debugreg.h
@@ -94,25 +94,6 @@ extern void aout_dump_debugregs(struct user *dump);

extern void hw_breakpoint_restore(void);

-#ifdef CONFIG_X86_64
-DECLARE_PER_CPU(int, debug_stack_usage);
-static inline void debug_stack_usage_inc(void)
-{
- __this_cpu_inc(debug_stack_usage);
-}
-static inline void debug_stack_usage_dec(void)
-{
- __this_cpu_dec(debug_stack_usage);
-}
-void debug_stack_set_zero(void);
-void debug_stack_reset(void);
-#else /* !X86_64 */
-static inline void debug_stack_set_zero(void) { }
-static inline void debug_stack_reset(void) { }
-static inline void debug_stack_usage_inc(void) { }
-static inline void debug_stack_usage_dec(void) { }
-#endif /* X86_64 */
-
static __always_inline unsigned long local_db_save(void)
{
unsigned long dr7;
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index d6c3d34..07632f3 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -42,8 +42,6 @@ static inline void fill_ldt(struct desc_struct *desc, const struct user_desc *in

extern struct desc_ptr idt_descr;
extern gate_desc idt_table[];
-extern const struct desc_ptr debug_idt_descr;
-extern gate_desc debug_idt_table[];

struct gdt_page {
struct desc_struct gdt[GDT_ENTRIES];
@@ -390,31 +388,6 @@ void alloc_intr_gate(unsigned int n, const void *addr);

extern unsigned long system_vectors[];

-#ifdef CONFIG_X86_64
-DECLARE_PER_CPU(u32, debug_idt_ctr);
-static __always_inline bool is_debug_idt_enabled(void)
-{
- if (this_cpu_read(debug_idt_ctr))
- return true;
-
- return false;
-}
-
-static __always_inline void load_debug_idt(void)
-{
- load_idt((const struct desc_ptr *)&debug_idt_descr);
-}
-#else
-static inline bool is_debug_idt_enabled(void)
-{
- return false;
-}
-
-static inline void load_debug_idt(void)
-{
-}
-#endif
-
/*
* The load_current_idt() must be called with interrupts disabled
* to avoid races. That way the IDT will always be set back to the expected
@@ -424,10 +397,7 @@ static inline void load_debug_idt(void)
*/
static __always_inline void load_current_idt(void)
{
- if (is_debug_idt_enabled())
- load_debug_idt();
- else
- load_idt((const struct desc_ptr *)&idt_descr);
+ load_idt((const struct desc_ptr *)&idt_descr);
}

extern void idt_setup_early_handler(void);
@@ -438,11 +408,9 @@ extern void idt_setup_apic_and_irq_gates(void);
#ifdef CONFIG_X86_64
extern void idt_setup_early_pf(void);
extern void idt_setup_ist_traps(void);
-extern void idt_setup_debugidt_traps(void);
#else
static inline void idt_setup_early_pf(void) { }
static inline void idt_setup_ist_traps(void) { }
-static inline void idt_setup_debugidt_traps(void) { }
#endif

extern void idt_invalidate(void *addr);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6751b81..c55be3b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1689,23 +1689,6 @@ void syscall_init(void)
X86_EFLAGS_IOPL|X86_EFLAGS_AC|X86_EFLAGS_NT);
}

-DEFINE_PER_CPU(int, debug_stack_usage);
-DEFINE_PER_CPU(u32, debug_idt_ctr);
-
-noinstr void debug_stack_set_zero(void)
-{
- this_cpu_inc(debug_idt_ctr);
- load_current_idt();
-}
-
-noinstr void debug_stack_reset(void)
-{
- if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
- return;
- if (this_cpu_dec_return(debug_idt_ctr) == 0)
- load_current_idt();
-}
-
#else /* CONFIG_X86_64 */

DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index bc9b0d1..226c992 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -158,14 +158,6 @@ static const __initconst struct idt_data apic_idts[] = {
static const __initconst struct idt_data early_pf_idts[] = {
INTG(X86_TRAP_PF, asm_exc_page_fault),
};
-
-/*
- * Override for the debug_idt. Same as the default, but with interrupt
- * stack set to DEFAULT_STACK (0). Required for NMI trap handling.
- */
-static const __initconst struct idt_data dbg_idts[] = {
- INTG(X86_TRAP_DB, asm_exc_debug),
-};
#endif

/* Must be page-aligned because the real IDT is used in a fixmap. */
@@ -177,9 +169,6 @@ struct desc_ptr idt_descr __ro_after_init = {
};

#ifdef CONFIG_X86_64
-/* No need to be aligned, but done to keep all IDTs defined the same way. */
-gate_desc debug_idt_table[IDT_ENTRIES] __page_aligned_bss;
-
/*
* The exceptions which use Interrupt stacks. They are setup after
* cpu_init() when the TSS has been initialized.
@@ -192,15 +181,6 @@ static const __initconst struct idt_data ist_idts[] = {
ISTG(X86_TRAP_MC, asm_exc_machine_check, IST_INDEX_MCE),
#endif
};
-
-/*
- * Override for the debug_idt. Same as the default, but with interrupt
- * stack set to DEFAULT_STACK (0). Required for NMI trap handling.
- */
-const struct desc_ptr debug_idt_descr = {
- .size = IDT_ENTRIES * 16 - 1,
- .address = (unsigned long) debug_idt_table,
-};
#endif

static inline void idt_init_desc(gate_desc *gate, const struct idt_data *d)
@@ -292,16 +272,6 @@ void __init idt_setup_ist_traps(void)
{
idt_setup_from_table(idt_table, ist_idts, ARRAY_SIZE(ist_idts), true);
}
-
-/**
- * idt_setup_debugidt_traps - Initialize the debug idt table with debug traps
- */
-void __init idt_setup_debugidt_traps(void)
-{
- memcpy(&debug_idt_table, &idt_table, IDT_ENTRIES * 16);
-
- idt_setup_from_table(debug_idt_table, dbg_idts, ARRAY_SIZE(dbg_idts), false);
-}
#endif

/**
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bcb9dd9..6f887be 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -798,12 +798,6 @@ static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,
return;
}

- /*
- * Let others (NMI) know that the debug stack is in use
- * as we may switch to the interrupt stack.
- */
- debug_stack_usage_inc();
-
/* It's safe to allow irq's after DR6 has been saved */
cond_local_irq_enable(regs);

@@ -831,7 +825,6 @@ static void noinstr handle_debug(struct pt_regs *regs, unsigned long dr6,

out:
cond_local_irq_disable(regs);
- debug_stack_usage_dec();
instrumentation_end();
}

@@ -1077,6 +1070,4 @@ void __init trap_init(void)
cpu_init();

idt_setup_ist_traps();
-
- idt_setup_debugidt_traps();
}