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    Subject[patch V4 part 3 07/29] 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 | 401 +++++++++++++++++++++++++---------------------
    1 file changed, 219 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>

    @@ -494,6 +495,202 @@ 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.
    *
    @@ -861,195 +1058,35 @@ 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_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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