x86/entry: Don't call error_entry() for XENPV

XENPV guests enter already on the task stack and they can't fault for
native_iret() nor native_load_gs_index() since they use their own pvop
for IRET and load_gs_index(). A CR3 switch is not needed either.

So there is no reason to call error_entry() in XENPV.

  [ 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/20220503032107.680190-6-jiangshanlai@gmail.com

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ab6ab6d..062aa9d 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -336,8 +336,17 @@ SYM_CODE_END(push_and_clear_regs)
        call push_and_clear_regs
        UNWIND_HINT_REGS
 
-       call    error_entry
-       movq    %rax, %rsp                      /* switch to the task stack if from userspace */
+       /*
+        * Call error_entry() and switch to the task stack if from userspace.
+        *
+        * 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 the CR3.  So it can skip invoking error_entry().
+        */
+       ALTERNATIVE "call error_entry; movq %rax, %rsp", \
+               "", X86_FEATURE_XENPV
+
        ENCODE_FRAME_POINTER
        UNWIND_HINT_REGS