linux-kernel - [patch V4 part 5 26/31] x86/entry/64: Remove IRQ stack switching ASM

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Date:   Tue, 05 May 2020 15:54:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: [patch V4 part 5 26/31] x86/entry/64: Remove IRQ stack switching ASM

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/entry/entry_64.S |   96 ----------------------------------------------
 1 file changed, 96 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -371,102 +371,6 @@ SYM_CODE_END(ret_from_fork)
 #endif
 .endm
 
-/*
- * Enters the IRQ stack if we're not already using it.  NMI-safe.  Clobbers
- * flags and puts old RSP into old_rsp, and leaves all other GPRs alone.
- * Requires kernel GSBASE.
- *
- * The invariant is that, if irq_count != -1, then the IRQ stack is in use.
- */
-.macro ENTER_IRQ_STACK regs=1 old_rsp save_ret=0
-	DEBUG_ENTRY_ASSERT_IRQS_OFF
-
-	.if \save_ret
-	/*
-	 * If save_ret is set, the original stack contains one additional
-	 * entry -- the return address. Therefore, move the address one
-	 * entry below %rsp to \old_rsp.
-	 */
-	leaq	8(%rsp), \old_rsp
-	.else
-	movq	%rsp, \old_rsp
-	.endif
-
-	.if \regs
-	UNWIND_HINT_REGS base=\old_rsp
-	.endif
-
-	incl	PER_CPU_VAR(irq_count)
-	jnz	.Lirq_stack_push_old_rsp_\@
-
-	/*
-	 * Right now, if we just incremented irq_count to zero, we've
-	 * claimed the IRQ stack but we haven't switched to it yet.
-	 *
-	 * If anything is added that can interrupt us here without using IST,
-	 * it must be *extremely* careful to limit its stack usage.  This
-	 * could include kprobes and a hypothetical future IST-less #DB
-	 * handler.
-	 *
-	 * The OOPS unwinder relies on the word at the top of the IRQ
-	 * stack linking back to the previous RSP for the entire time we're
-	 * on the IRQ stack.  For this to work reliably, we need to write
-	 * it before we actually move ourselves to the IRQ stack.
-	 */
-
-	movq	\old_rsp, PER_CPU_VAR(irq_stack_backing_store + IRQ_STACK_SIZE - 8)
-	movq	PER_CPU_VAR(hardirq_stack_ptr), %rsp
-
-#ifdef CONFIG_DEBUG_ENTRY
-	/*
-	 * If the first movq above becomes wrong due to IRQ stack layout
-	 * changes, the only way we'll notice is if we try to unwind right
-	 * here.  Assert that we set up the stack right to catch this type
-	 * of bug quickly.
-	 */
-	cmpq	-8(%rsp), \old_rsp
-	je	.Lirq_stack_okay\@
-	ud2
-	.Lirq_stack_okay\@:
-#endif
-
-.Lirq_stack_push_old_rsp_\@:
-	pushq	\old_rsp
-
-	.if \regs
-	UNWIND_HINT_REGS indirect=1
-	.endif
-
-	.if \save_ret
-	/*
-	 * Push the return address to the stack. This return address can
-	 * be found at the "real" original RSP, which was offset by 8 at
-	 * the beginning of this macro.
-	 */
-	pushq	-8(\old_rsp)
-	.endif
-.endm
-
-/*
- * Undoes ENTER_IRQ_STACK.
- */
-.macro LEAVE_IRQ_STACK regs=1
-	DEBUG_ENTRY_ASSERT_IRQS_OFF
-	/* We need to be off the IRQ stack before decrementing irq_count. */
-	popq	%rsp
-
-	.if \regs
-	UNWIND_HINT_REGS
-	.endif
-
-	/*
-	 * As in ENTER_IRQ_STACK, irq_count == 0, we are still claiming
-	 * the irq stack but we're not on it.
-	 */
-
-	decl	PER_CPU_VAR(irq_count)
-.endm
-
 /**
  * idtentry_body - Macro to emit code calling the C function
  * @cfunc:		C function to be called