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    Subject[PATCH 06/11] x86/entry: Don't call error_entry for XENPV
    Date
    From: Lai Jiangshan <laijs@linux.alibaba.com>

    When in XENPV, it is already in the task stack, and it can't fault
    for native_iret() nor native_load_gs_index() since XENPV uses its own
    pvops for iret and load_gs_index(). And it doesn't need to switch CR3.
    So there is no reason to call error_entry() in XENPV.

    Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
    ---
    arch/x86/entry/entry_64.S | 13 +++++++++++--
    1 file changed, 11 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
    index ee1d4adcdab0..383070aa9272 100644
    --- a/arch/x86/entry/entry_64.S
    +++ b/arch/x86/entry/entry_64.S
    @@ -325,8 +325,17 @@ SYM_CODE_END(ret_from_fork)
    PUSH_AND_CLEAR_REGS
    ENCODE_FRAME_POINTER

    - call error_entry
    - movq %rax, %rsp /* switch stack settled by sync_regs() */
    + /*
    + * Call error_entry and switch stack settled by sync_regs().
    + *
    + * When in XENPV, it is already in the task stack, and it can't fault
    + * for native_iret() nor native_load_gs_index() since XENPV uses its
    + * own pvops for iret and load_gs_index(). And it doesn't need to
    + * switch CR3. So it can skip invoking error_entry().
    + */
    + ALTERNATIVE "call error_entry; movq %rax, %rsp", \
    + "", X86_FEATURE_XENPV
    +
    ENCODE_FRAME_POINTER
    UNWIND_HINT_REGS

    --
    2.19.1.6.gb485710b
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