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    Subject[tip:x86/pti] x86/entry/32: Simplify debug entry point
    Commit-ID:  929b44eb5739bf11d4a9bce85d7346bd955fc24d
    Gitweb: https://git.kernel.org/tip/929b44eb5739bf11d4a9bce85d7346bd955fc24d
    Author: Joerg Roedel <jroedel@suse.de>
    AuthorDate: Wed, 18 Jul 2018 11:40:48 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 20 Jul 2018 01:11:39 +0200

    x86/entry/32: Simplify debug entry point

    The common exception entry code now handles the entry-from-sysenter stack
    situation and makes sure to leave with the same stack as it entered the
    kernel.

    So there is no need anymore for the special handling in the debug entry
    code.

    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Tested-by: Pavel Machek <pavel@ucw.cz>
    Cc: "H . Peter Anvin" <hpa@zytor.com>
    Cc: linux-mm@kvack.org
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Jiri Kosina <jkosina@suse.cz>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: David Laight <David.Laight@aculab.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Eduardo Valentin <eduval@amazon.com>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: aliguori@amazon.com
    Cc: daniel.gruss@iaik.tugraz.at
    Cc: hughd@google.com
    Cc: keescook@google.com
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Waiman Long <llong@redhat.com>
    Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca>
    Cc: joro@8bytes.org
    Link: https://lkml.kernel.org/r/1531906876-13451-12-git-send-email-joro@8bytes.org

    ---
    arch/x86/entry/entry_32.S | 35 +++--------------------------------
    1 file changed, 3 insertions(+), 32 deletions(-)

    diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
    index 9d6eceba0461..dbf7d619dcd6 100644
    --- a/arch/x86/entry/entry_32.S
    +++ b/arch/x86/entry/entry_32.S
    @@ -1226,41 +1226,12 @@ END(common_exception)

    ENTRY(debug)
    /*
    - * #DB can happen at the first instruction of
    - * entry_SYSENTER_32 or in Xen's SYSENTER prologue. If this
    - * happens, then we will be running on a very small stack. We
    - * need to detect this condition and switch to the thread
    - * stack before calling any C code at all.
    - *
    - * If you edit this code, keep in mind that NMIs can happen in here.
    + * Entry from sysenter is now handled in common_exception
    */
    ASM_CLAC
    pushl $-1 # mark this as an int
    -
    - SAVE_ALL
    - ENCODE_FRAME_POINTER
    - xorl %edx, %edx # error code 0
    - movl %esp, %eax # pt_regs pointer
    -
    - /* Are we currently on the SYSENTER stack? */
    - movl PER_CPU_VAR(cpu_entry_area), %ecx
    - addl $CPU_ENTRY_AREA_entry_stack + SIZEOF_entry_stack, %ecx
    - subl %eax, %ecx /* ecx = (end of entry_stack) - esp */
    - cmpl $SIZEOF_entry_stack, %ecx
    - jb .Ldebug_from_sysenter_stack
    -
    - TRACE_IRQS_OFF
    - call do_debug
    - jmp ret_from_exception
    -
    -.Ldebug_from_sysenter_stack:
    - /* We're on the SYSENTER stack. Switch off. */
    - movl %esp, %ebx
    - movl PER_CPU_VAR(cpu_current_top_of_stack), %esp
    - TRACE_IRQS_OFF
    - call do_debug
    - movl %ebx, %esp
    - jmp ret_from_exception
    + pushl $do_debug
    + jmp common_exception
    END(debug)

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