[RFC PATCH v2 5/5] x86/entry/64: open-code switch_to_thread_stack

[Dominik Brodowski]

Open-code the two instances which used switch_to_thread_stack. This
allows us to remove the wrapper around DO_SWITCH_TO_THREAD_STACK.

While at it, update the UNWIND hint to reflect where the IRET frame is.

Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
---
 arch/x86/entry/entry_64.S        | 59 ++++++++++++++++------------------------
 arch/x86/entry/entry_64_compat.S | 19 ++++++++++++-
 2 files changed, 42 insertions(+), 36 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0ac2b4865d58..fa61be457082 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -539,17 +539,36 @@ END(irq_entries_start)
 .endm
 
 /*
- * Switch to the thread stack.  This is called with the IRET frame and
- * orig_ax on the stack.  (That is, RDI..R12 are not on the stack and
- * space has not been allocated for them.)
+ * Interrupt entry/exit.
+ *
+ * Interrupt entry points save only callee clobbered registers in fast path.
+ *
+ * Entry runs with interrupts off.
  */
-.macro DO_SWITCH_TO_THREAD_STACK
+/* 8(%rsp): ~(interrupt number) */
+ENTRY(interrupt_helper)
+	UNWIND_HINT_FUNC
+	cld
+
+	testb	$3, CS-ORIG_RAX+8(%rsp)
+	jz	1f
+	SWAPGS
+
+	/*
+	 * Switch to the thread stack.  The IRET frame and orig_ax are
+	 * on the stack, as well as the return address. RDI..R12 are
+	 * not (yet) on the stack and space has not (yet) been
+	 * allocated for them.
+	 */
 	pushq	%rdi
+
 	/* Need to switch before accessing the thread stack. */
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
 	movq	%rsp, %rdi
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
-	UNWIND_HINT sp_offset=16 sp_reg=ORC_REG_DI
+	 /* We have RDI, return address, and orig_ax on the stack on
+	  * top of the IRET frame. That means offset=24 */
+	UNWIND_HINT_IRET_REGS base=%rdi offset=24
 
 	pushq	7*8(%rdi)		/* regs->ss */
 	pushq	6*8(%rdi)		/* regs->rsp */
@@ -561,24 +580,6 @@ END(irq_entries_start)
 	UNWIND_HINT_FUNC
 
 	movq	(%rdi), %rdi
-.endm
-
-/*
- * Interrupt entry/exit.
- *
- * Interrupt entry points save only callee clobbered registers in fast path.
- *
- * Entry runs with interrupts off.
- */
-/* 8(%rsp): ~(interrupt number) */
-ENTRY(interrupt_helper)
-	UNWIND_HINT_FUNC
-	cld
-
-	testb	$3, CS-ORIG_RAX+8(%rsp)
-	jz	1f
-	SWAPGS
-	DO_SWITCH_TO_THREAD_STACK
 1:
 
 	PUSH_AND_CLEAR_REGS save_ret=1
@@ -880,18 +881,6 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
  */
 #define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8)
 
-#if defined(CONFIG_IA32_EMULATION)
-/* entry_64_compat.S::entry_INT80_compat expects this to be an ASM function */
-ENTRY(switch_to_thread_stack)
-	UNWIND_HINT_FUNC
-	cld
-
-	DO_SWITCH_TO_THREAD_STACK
-
-	ret
-END(switch_to_thread_stack)
-#endif
-
 .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
 ENTRY(\sym)
 	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 364ea4a207be..5b9503c7148d 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -350,7 +350,24 @@ ENTRY(entry_INT80_compat)
 	pushq	%rax			/* pt_regs->orig_ax */
 
 	/* switch to thread stack expects orig_ax to be pushed */
-	call	switch_to_thread_stack
+	pushq	%rdi
+
+	/* Need to switch before accessing the thread stack. */
+	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
+	movq	%rsp, %rdi
+	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
+	 /* We have RDI and orig_ax on the stack on top of the IRET frame.
+	  * That means offset=16 */
+	UNWIND_HINT_IRET_REGS base=%rdi offset=16
+
+	pushq	6*8(%rdi)		/* regs->ss */
+	pushq	5*8(%rdi)		/* regs->rsp */
+	pushq	4*8(%rdi)		/* regs->eflags */
+	pushq	3*8(%rdi)		/* regs->cs */
+	pushq	2*8(%rdi)		/* regs->ip */
+	pushq	1*8(%rdi)		/* regs->orig_ax */
+
+	movq	(%rdi), %rdi		/* restore %rdi */
 
 	pushq	%rdi			/* pt_regs->di */
 	pushq	%rsi			/* pt_regs->si */
-- 
2.16.1