x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()

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

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index ca3e99e..b1cef3b 100644 (file)
--- 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
@@ -985,13 +996,11 @@ 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