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Subject[PATCH V6 21/49] 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
at native_irq_return_iret nor asm_load_gs_index_gs_change 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().

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 09bd77e49249..c09e5a4dfbbf 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
+ * at native_irq_return_iret nor asm_load_gs_index_gs_change 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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