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Subject[patch part-III V2 04/23] x86/entry: Distangle idtentry
From: Thomas Gleixner <tglx@linutronix.de>

idtentry is a completely unreadable maze. Split it into distinct idtentry
variants which only contain the minimal code:

- idtentry for regular exceptions
- idtentry_mce_debug for #MCE and #DB
- idtentry_df for #DF

The generated binary code is equivalent.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

---
arch/x86/entry/entry_64.S | 402 +++++++++++++++++++++++++---------------------
1 file changed, 220 insertions(+), 182 deletions(-)

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -37,6 +37,7 @@
#include <asm/pgtable_types.h>
#include <asm/export.h>
#include <asm/frame.h>
+#include <asm/trapnr.h>
#include <asm/nospec-branch.h>
#include <linux/err.h>

@@ -490,6 +491,202 @@ SYM_CODE_END(spurious_entries_start)
decl PER_CPU_VAR(irq_count)
.endm

+/**
+ * idtentry_body - Macro to emit code calling the C function
+ * @vector: Vector number
+ * @cfunc: C function to be called
+ * @has_error_code: Hardware pushed error code on stack
+ */
+.macro idtentry_body vector cfunc has_error_code:req
+
+ call error_entry
+ UNWIND_HINT_REGS
+
+ .if \vector == X86_TRAP_PF
+ /*
+ * Store CR2 early so subsequent faults cannot clobber it. Use R12 as
+ * intermediate storage as RDX can be clobbered in enter_from_user_mode().
+ * GET_CR2_INTO can clobber RAX.
+ */
+ GET_CR2_INTO(%r12);
+ .endif
+
+ TRACE_IRQS_OFF
+
+#ifdef CONFIG_CONTEXT_TRACKING
+ testb $3, CS(%rsp)
+ jz .Lfrom_kernel_no_ctxt_tracking_\@
+ CALL_enter_from_user_mode
+.Lfrom_kernel_no_ctxt_tracking_\@:
+#endif
+
+ movq %rsp, %rdi /* pt_regs pointer into 1st argument*/
+
+ .if \has_error_code == 1
+ movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/
+ movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
+ .else
+ xorl %esi, %esi /* Clear the error code */
+ .endif
+
+ .if \vector == X86_TRAP_PF
+ movq %r12, %rdx /* Move CR2 into 3rd argument */
+ .endif
+
+ call \cfunc
+
+ jmp error_exit
+.endm
+
+/**
+ * idtentry - Macro to generate entry stubs for simple IDT entries
+ * @vector: Vector number
+ * @asmsym: ASM symbol for the entry point
+ * @cfunc: C function to be called
+ * @has_error_code: Hardware pushed error code on stack
+ *
+ * The macro emits code to set up the kernel context for straight forward
+ * and simple IDT entries. No IST stack, no paranoid entry checks.
+ */
+.macro idtentry vector asmsym cfunc has_error_code:req
+SYM_CODE_START(\asmsym)
+ UNWIND_HINT_IRET_REGS offset=\has_error_code*8
+ ASM_CLAC
+
+ .if \has_error_code == 0
+ pushq $-1 /* ORIG_RAX: no syscall to restart */
+ .endif
+
+ .if \vector == X86_TRAP_BP
+ /*
+ * If coming from kernel space, create a 6-word gap to allow the
+ * int3 handler to emulate a call instruction.
+ */
+ testb $3, CS-ORIG_RAX(%rsp)
+ jnz .Lfrom_usermode_no_gap_\@
+ .rept 6
+ pushq 5*8(%rsp)
+ .endr
+ UNWIND_HINT_IRET_REGS offset=8
+.Lfrom_usermode_no_gap_\@:
+ .endif
+
+ idtentry_body \vector \cfunc \has_error_code
+
+_ASM_NOKPROBE(\asmsym)
+SYM_CODE_END(\asmsym)
+.endm
+
+/*
+ * MCE and DB exceptions
+ */
+#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + (x) * 8)
+
+/**
+ * idtentry_mce_db - Macro to generate entry stubs for #MC and #DB
+ * @vector: Vector number
+ * @asmsym: ASM symbol for the entry point
+ * @cfunc: C function to be called
+ *
+ * The macro emits code to set up the kernel context for #MC and #DB
+ *
+ * If the entry comes from user space it uses the normal entry path
+ * including the return to user space work and preemption checks on
+ * exit.
+ *
+ * If hits in kernel mode then it needs to go through the paranoid
+ * entry as the exception can hit any random state. No preemption
+ * check on exit to keep the paranoid path simple.
+ *
+ * If the trap is #DB then the interrupt stack entry in the IST is
+ * moved to the second stack, so a potential recursion will have a
+ * fresh IST.
+ */
+.macro idtentry_mce_db vector asmsym cfunc
+SYM_CODE_START(\asmsym)
+ UNWIND_HINT_IRET_REGS
+ ASM_CLAC
+
+ pushq $-1 /* ORIG_RAX: no syscall to restart */
+
+ /*
+ * If the entry is from userspace, switch stacks and treat it as
+ * a normal entry.
+ */
+ testb $3, CS-ORIG_RAX(%rsp)
+ jnz .Lfrom_usermode_switch_stack_\@
+
+ /*
+ * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
+ * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
+ */
+ call paranoid_entry
+
+ UNWIND_HINT_REGS
+
+ .if \vector == X86_TRAP_DB
+ TRACE_IRQS_OFF_DEBUG
+ .else
+ TRACE_IRQS_OFF
+ .endif
+
+ movq %rsp, %rdi /* pt_regs pointer */
+ xorl %esi, %esi /* Clear the error code */
+
+ .if \vector == X86_TRAP_DB
+ subq $DB_STACK_OFFSET, CPU_TSS_IST(IST_INDEX_DB)
+ .endif
+
+ call \cfunc
+
+ .if \vector == X86_TRAP_DB
+ addq $DB_STACK_OFFSET, CPU_TSS_IST(IST_INDEX_DB)
+ .endif
+
+ jmp paranoid_exit
+
+ /* Switch to the regular task stack and use the noist entry point */
+.Lfrom_usermode_switch_stack_\@:
+ idtentry_body vector \cfunc, has_error_code=0
+
+_ASM_NOKPROBE(\asmsym)
+SYM_CODE_END(\asmsym)
+.endm
+
+/*
+ * Double fault entry. Straight paranoid. No checks from which context
+ * this comes because for the espfix induced #DF this would do the wrong
+ * thing.
+ */
+.macro idtentry_df vector asmsym cfunc
+SYM_CODE_START(\asmsym)
+ UNWIND_HINT_IRET_REGS offset=8
+ ASM_CLAC
+
+ /*
+ * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
+ * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
+ */
+ call paranoid_entry
+ UNWIND_HINT_REGS
+
+ /* Read CR2 early */
+ GET_CR2_INTO(%r12);
+
+ TRACE_IRQS_OFF
+
+ movq %rsp, %rdi /* pt_regs pointer into first argument */
+ movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/
+ movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
+ movq %r12, %rdx /* Move CR2 into 3rd argument */
+ call \cfunc
+
+ jmp paranoid_exit
+
+_ASM_NOKPROBE(\asmsym)
+SYM_CODE_END(\asmsym)
+.endm
+
/*
* Interrupt entry helper function.
*
@@ -857,197 +1054,38 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
/*
* Exception entry points.
*/
-#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + (x) * 8)
-
-.macro idtentry_part do_sym, has_error_code:req, read_cr2:req, paranoid:req, shift_ist=-1, ist_offset=0
-
- .if \paranoid
- call paranoid_entry
- /* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
- .else
- call error_entry
- .endif
- UNWIND_HINT_REGS
-
- .if \read_cr2
- /*
- * Store CR2 early so subsequent faults cannot clobber it. Use R12 as
- * intermediate storage as RDX can be clobbered in enter_from_user_mode().
- * GET_CR2_INTO can clobber RAX.
- */
- GET_CR2_INTO(%r12);
- .endif
-
- .if \shift_ist != -1
- TRACE_IRQS_OFF_DEBUG /* reload IDT in case of recursion */
- .else
- TRACE_IRQS_OFF
- .endif
-
-#ifdef CONFIG_CONTEXT_TRACKING
- .if \paranoid == 0
- testb $3, CS(%rsp)
- jz .Lfrom_kernel_no_context_tracking_\@
- CALL_enter_from_user_mode
-.Lfrom_kernel_no_context_tracking_\@:
- .endif
-#endif
-
- movq %rsp, %rdi /* pt_regs pointer */
-
- .if \has_error_code
- movq ORIG_RAX(%rsp), %rsi /* get error code */
- movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
- .else
- xorl %esi, %esi /* no error code */
- .endif
-
- .if \shift_ist != -1
- subq $\ist_offset, CPU_TSS_IST(\shift_ist)
- .endif
-
- .if \read_cr2
- movq %r12, %rdx /* Move CR2 into 3rd argument */
- .endif
-
- call \do_sym
-
- .if \shift_ist != -1
- addq $\ist_offset, CPU_TSS_IST(\shift_ist)
- .endif
-
- .if \paranoid
- /* this procedure expect "no swapgs" flag in ebx */
- jmp paranoid_exit
- .else
- jmp error_exit
- .endif
-
-.endm
-
-/**
- * idtentry - Generate an IDT entry stub
- * @sym: Name of the generated entry point
- * @do_sym: C function to be called
- * @has_error_code: True if this IDT vector has an error code on the stack
- * @paranoid: non-zero means that this vector may be invoked from
- * kernel mode with user GSBASE and/or user CR3.
- * 2 is special -- see below.
- * @shift_ist: Set to an IST index if entries from kernel mode should
- * decrement the IST stack so that nested entries get a
- * fresh stack. (This is for #DB, which has a nasty habit
- * of recursing.)
- * @create_gap: create a 6-word stack gap when coming from kernel mode.
- * @read_cr2: load CR2 into the 3rd argument; done before calling any C code
- *
- * idtentry generates an IDT stub that sets up a usable kernel context,
- * creates struct pt_regs, and calls @do_sym. The stub has the following
- * special behaviors:
- *
- * On an entry from user mode, the stub switches from the trampoline or
- * IST stack to the normal thread stack. On an exit to user mode, the
- * normal exit-to-usermode path is invoked.
- *
- * On an exit to kernel mode, if @paranoid == 0, we check for preemption,
- * whereas we omit the preemption check if @paranoid != 0. This is purely
- * because the implementation is simpler this way. The kernel only needs
- * to check for asynchronous kernel preemption when IRQ handlers return.
- *
- * If @paranoid == 0, then the stub will handle IRET faults by pretending
- * that the fault came from user mode. It will handle gs_change faults by
- * pretending that the fault happened with kernel GSBASE. Since this handling
- * is omitted for @paranoid != 0, the #GP, #SS, and #NP stubs must have
- * @paranoid == 0. This special handling will do the wrong thing for
- * espfix-induced #DF on IRET, so #DF must not use @paranoid == 0.
- *
- * @paranoid == 2 is special: the stub will never switch stacks. This is for
- * #DF: if the thread stack is somehow unusable, we'll still get a useful OOPS.
- */
-.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1 ist_offset=0 create_gap=0 read_cr2=0
-SYM_CODE_START(\sym)
- UNWIND_HINT_IRET_REGS offset=\has_error_code*8
-
- /* Sanity check */
- .if \shift_ist != -1 && \paranoid != 1
- .error "using shift_ist requires paranoid=1"
- .endif
-
- .if \create_gap && \paranoid
- .error "using create_gap requires paranoid=0"
- .endif
-
- ASM_CLAC
-
- .if \has_error_code == 0
- pushq $-1 /* ORIG_RAX: no syscall to restart */
- .endif
-
- .if \paranoid == 1
- testb $3, CS-ORIG_RAX(%rsp) /* If coming from userspace, switch stacks */
- jnz .Lfrom_usermode_switch_stack_\@
- .endif
-
- .if \create_gap == 1
- /*
- * If coming from kernel space, create a 6-word gap to allow the
- * int3 handler to emulate a call instruction.
- */
- testb $3, CS-ORIG_RAX(%rsp)
- jnz .Lfrom_usermode_no_gap_\@
- .rept 6
- pushq 5*8(%rsp)
- .endr
- UNWIND_HINT_IRET_REGS offset=8
-.Lfrom_usermode_no_gap_\@:
- .endif
-
- idtentry_part \do_sym, \has_error_code, \read_cr2, \paranoid, \shift_ist, \ist_offset
-
- .if \paranoid == 1
- /*
- * Entry from userspace. Switch stacks and treat it
- * as a normal entry. This means that paranoid handlers
- * run in real process context if user_mode(regs).
- */
-.Lfrom_usermode_switch_stack_\@:
- idtentry_part \do_sym, \has_error_code, \read_cr2, paranoid=0
- .endif
-
-_ASM_NOKPROBE(\sym)
-SYM_CODE_END(\sym)
-.endm

-idtentry divide_error do_divide_error has_error_code=0
-idtentry overflow do_overflow has_error_code=0
-idtentry int3 do_int3 has_error_code=0 create_gap=1
-idtentry bounds do_bounds has_error_code=0
-idtentry invalid_op do_invalid_op has_error_code=0
-idtentry device_not_available do_device_not_available has_error_code=0
-idtentry coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
-idtentry invalid_TSS do_invalid_TSS has_error_code=1
-idtentry segment_not_present do_segment_not_present has_error_code=1
-idtentry stack_segment do_stack_segment has_error_code=1
-idtentry general_protection do_general_protection has_error_code=1
-idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0
-idtentry coprocessor_error do_coprocessor_error has_error_code=0
-idtentry alignment_check do_alignment_check has_error_code=1
-idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0
+idtentry X86_TRAP_DE divide_error do_divide_error has_error_code=0
+idtentry X86_TRAP_OF overflow do_overflow has_error_code=0
+idtentry X86_TRAP_BP int3 do_int3 has_error_code=0
+idtentry X86_TRAP_BR bounds do_bounds has_error_code=0
+idtentry X86_TRAP_UD invalid_op do_invalid_op has_error_code=0
+idtentry X86_TRAP_NM device_not_available do_device_not_available has_error_code=0
+idtentry X86_TRAP_OLD_MF coprocessor_segment_overrun do_coprocessor_segment_overrun has_error_code=0
+idtentry X86_TRAP_TS invalid_TSS do_invalid_TSS has_error_code=1
+idtentry X86_TRAP_NP segment_not_present do_segment_not_present has_error_code=1
+idtentry X86_TRAP_SS stack_segment do_stack_segment has_error_code=1
+idtentry X86_TRAP_GP general_protection do_general_protection has_error_code=1
+idtentry X86_TRAP_SPURIOUS spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0
+idtentry X86_TRAP_MF coprocessor_error do_coprocessor_error has_error_code=0
+idtentry X86_TRAP_AC alignment_check do_alignment_check has_error_code=1
+idtentry X86_TRAP_XF simd_coprocessor_error do_simd_coprocessor_error has_error_code=0

-idtentry page_fault do_page_fault has_error_code=1 read_cr2=1
+idtentry X86_TRAP_PF page_fault do_page_fault has_error_code=1
#ifdef CONFIG_KVM_GUEST
-idtentry async_page_fault do_async_page_fault has_error_code=1 read_cr2=1
+idtentry X86_TRAP_PF async_page_fault do_async_page_fault has_error_code=1
#endif

#ifdef CONFIG_X86_MCE
-idtentry machine_check do_mce has_error_code=0 paranoid=1
+idtentry_mce_db X86_TRAP_MCE machine_check do_mce
#endif
-idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=IST_INDEX_DB ist_offset=DB_STACK_OFFSET
-idtentry double_fault do_double_fault has_error_code=1 paranoid=2 read_cr2=1
+idtentry_mce_db X86_TRAP_DB debug do_debug
+idtentry_df X86_TRAP_DF double_fault do_double_fault

#ifdef CONFIG_XEN_PV
-idtentry hypervisor_callback xen_do_hypervisor_callback has_error_code=0
-idtentry xennmi do_nmi has_error_code=0
-idtentry xendebug do_debug has_error_code=0
+idtentry 512 /* dummy */ hypervisor_callback xen_do_hypervisor_callback has_error_code=0
+idtentry X86_TRAP_NMI xennmi do_nmi has_error_code=0
+idtentry X86_TRAP_DB xendebug do_debug has_error_code=0
#endif

/*
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