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    Subject[PATCH 5.18 03/61] x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()
    Date
    From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

    commit ee774dac0da1543376a69fd90840af6aa86879b3 upstream.

    The macro idtentry() (through idtentry_body()) calls error_entry()
    unconditionally even on XENPV. But XENPV needs to only push and clear
    regs.

    PUSH_AND_CLEAR_REGS in error_entry() makes the stack not return to its
    original place when the function returns, which means it is not possible
    to convert it to a C function.

    Carve out PUSH_AND_CLEAR_REGS out of error_entry() and into a separate
    function and call it before error_entry() in order to avoid calling
    error_entry() on XENPV.

    It will also allow for error_entry() to be converted to C code that can
    use inlined sync_regs() and save a function call.

    [ bp: Massage commit message. ]

    Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Juergen Gross <jgross@suse.com>
    Link: https://lore.kernel.org/r/20220503032107.680190-4-jiangshanlai@gmail.com
    Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/entry/entry_64.S | 15 ++++++++++++---
    1 file changed, 12 insertions(+), 3 deletions(-)

    --- a/arch/x86/entry/entry_64.S
    +++ b/arch/x86/entry/entry_64.S
    @@ -318,6 +318,14 @@ SYM_CODE_END(ret_from_fork)
    #endif
    .endm

    +/* Save all registers in pt_regs */
    +SYM_CODE_START_LOCAL(push_and_clear_regs)
    + UNWIND_HINT_FUNC
    + PUSH_AND_CLEAR_REGS save_ret=1
    + ENCODE_FRAME_POINTER 8
    + RET
    +SYM_CODE_END(push_and_clear_regs)
    +
    /**
    * idtentry_body - Macro to emit code calling the C function
    * @cfunc: C function to be called
    @@ -325,6 +333,9 @@ SYM_CODE_END(ret_from_fork)
    */
    .macro idtentry_body cfunc has_error_code:req

    + call push_and_clear_regs
    + UNWIND_HINT_REGS
    +
    call error_entry
    movq %rax, %rsp /* switch to the task stack if from userspace */
    ENCODE_FRAME_POINTER
    @@ -986,13 +997,11 @@ SYM_CODE_START_LOCAL(paranoid_exit)
    SYM_CODE_END(paranoid_exit)

    /*
    - * Save all registers in pt_regs, and switch GS if needed.
    + * Switch GS and CR3 if needed.
    */
    SYM_CODE_START_LOCAL(error_entry)
    UNWIND_HINT_FUNC
    cld
    - PUSH_AND_CLEAR_REGS save_ret=1
    - ENCODE_FRAME_POINTER 8
    testb $3, CS+8(%rsp)
    jz .Lerror_kernelspace


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