102 lines
3.2 KiB
Diff
102 lines
3.2 KiB
Diff
From: Steven Rostedt <rostedt@goodmis.org>
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Subject: x86: Do not disable preemption in int3 on 32bit
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.8-rt6.tar.xz
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Preemption must be disabled before enabling interrupts in do_trap
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on x86_64 because the stack in use for int3 and debug is a per CPU
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stack set by th IST. But 32bit does not have an IST and the stack
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still belongs to the current task and there is no problem in scheduling
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out the task.
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Keep preemption enabled on X86_32 when enabling interrupts for
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do_trap().
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The name of the function is changed from preempt_conditional_sti/cli()
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to conditional_sti/cli_ist(), to annotate that this function is used
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when the stack is on the IST.
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Cc: stable-rt@vger.kernel.org
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Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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arch/x86/kernel/traps.c | 28 +++++++++++++++++++++-------
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1 file changed, 21 insertions(+), 7 deletions(-)
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--- a/arch/x86/kernel/traps.c
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+++ b/arch/x86/kernel/traps.c
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@@ -88,9 +88,21 @@ static inline void conditional_sti(struc
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local_irq_enable();
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}
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-static inline void preempt_conditional_sti(struct pt_regs *regs)
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+static inline void conditional_sti_ist(struct pt_regs *regs)
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{
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+#ifdef CONFIG_X86_64
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+ /*
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+ * X86_64 uses a per CPU stack on the IST for certain traps
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+ * like int3. The task can not be preempted when using one
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+ * of these stacks, thus preemption must be disabled, otherwise
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+ * the stack can be corrupted if the task is scheduled out,
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+ * and another task comes in and uses this stack.
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+ *
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+ * On x86_32 the task keeps its own stack and it is OK if the
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+ * task schedules out.
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+ */
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preempt_count_inc();
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+#endif
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if (regs->flags & X86_EFLAGS_IF)
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local_irq_enable();
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}
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@@ -101,11 +113,13 @@ static inline void conditional_cli(struc
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local_irq_disable();
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}
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-static inline void preempt_conditional_cli(struct pt_regs *regs)
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+static inline void conditional_cli_ist(struct pt_regs *regs)
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{
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if (regs->flags & X86_EFLAGS_IF)
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local_irq_disable();
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+#ifdef CONFIG_X86_64
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preempt_count_dec();
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+#endif
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}
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enum ctx_state ist_enter(struct pt_regs *regs)
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@@ -539,9 +553,9 @@ dotraplinkage void notrace do_int3(struc
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* as we may switch to the interrupt stack.
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*/
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debug_stack_usage_inc();
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- preempt_conditional_sti(regs);
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+ conditional_sti_ist(regs);
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do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL);
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- preempt_conditional_cli(regs);
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+ conditional_cli_ist(regs);
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debug_stack_usage_dec();
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exit:
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ist_exit(regs, prev_state);
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@@ -671,12 +685,12 @@ dotraplinkage void do_debug(struct pt_re
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debug_stack_usage_inc();
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/* It's safe to allow irq's after DR6 has been saved */
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- preempt_conditional_sti(regs);
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+ conditional_sti_ist(regs);
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if (regs->flags & X86_VM_MASK) {
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handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
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X86_TRAP_DB);
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- preempt_conditional_cli(regs);
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+ conditional_cli_ist(regs);
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debug_stack_usage_dec();
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goto exit;
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}
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@@ -696,7 +710,7 @@ dotraplinkage void do_debug(struct pt_re
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si_code = get_si_code(tsk->thread.debugreg6);
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if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
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send_sigtrap(tsk, regs, error_code, si_code);
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- preempt_conditional_cli(regs);
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+ conditional_cli_ist(regs);
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debug_stack_usage_dec();
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exit:
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