x86/lib/copy_page_64.S: Use generic ALTERNATIVE macro

... instead of the semi-version with the spelled out sections.

What is more, make the REP_GOOD version be the default copy_page()
version as the majority of the relevant x86 CPUs do set
X86_FEATURE_REP_GOOD. Thus, copy_page gets compiled to:

  ffffffff8130af80 <copy_page>:
  ffffffff8130af80:       e9 0b 00 00 00          jmpq   ffffffff8130af90 <copy_page_regs>
  ffffffff8130af85:       b9 00 02 00 00          mov    $0x200,%ecx
  ffffffff8130af8a:       f3 48 a5                rep movsq %ds:(%rsi),%es:(%rdi)
  ffffffff8130af8d:       c3                      retq
  ffffffff8130af8e:       66 90                   xchg   %ax,%ax

  ffffffff8130af90 <copy_page_regs>:
  ...

and after the alternatives have run, the JMP to the old, unrolled
version gets NOPed out:

  ffffffff8130af80 <copy_page>:
  ffffffff8130af80:  66 66 90		xchg   %ax,%ax
  ffffffff8130af83:  66 90		xchg   %ax,%ax
  ffffffff8130af85:  b9 00 02 00 00	mov    $0x200,%ecx
  ffffffff8130af8a:  f3 48 a5		rep movsq %ds:(%rsi),%es:(%rdi)
  ffffffff8130af8d:  c3			retq

On modern uarches, those NOPs are cheaper than the unconditional JMP
previously.

Signed-off-by: Borislav Petkov <bp@suse.de>

1 files changed, 12 insertions, 25 deletions

diff --git a/arch/x86/lib/copy_page_64.S b/arch/x86/lib/copy_page_64.S
index f1ffdbb07755..8239dbcbf984 100644
--- a/arch/x86/lib/copy_page_64.S
+++ b/arch/x86/lib/copy_page_64.S
@@ -2,23 +2,26 @@
 
 #include <linux/linkage.h>
 #include <asm/dwarf2.h>
+#include <asm/cpufeature.h>
 #include <asm/alternative-asm.h>
 
+/*
+ * Some CPUs run faster using the string copy instructions (sane microcode).
+ * It is also a lot simpler. Use this when possible. But, don't use streaming
+ * copy unless the CPU indicates X86_FEATURE_REP_GOOD. Could vary the
+ * prefetch distance based on SMP/UP.
+ */
         ALIGN
-copy_page_rep:
+ENTRY(copy_page)
         CFI_STARTPROC
+        ALTERNATIVE "jmp copy_page_regs", "", X86_FEATURE_REP_GOOD
         movl    $4096/8, %ecx
         rep     movsq
         ret
         CFI_ENDPROC
-ENDPROC(copy_page_rep)
-
-/*
- *  Don't use streaming copy unless the CPU indicates X86_FEATURE_REP_GOOD.
- *  Could vary the prefetch distance based on SMP/UP.
-*/
+ENDPROC(copy_page)
 
-ENTRY(copy_page)
+ENTRY(copy_page_regs)
         CFI_STARTPROC
         subq    $2*8,   %rsp
         CFI_ADJUST_CFA_OFFSET 2*8
@@ -90,21 +93,5 @@ ENTRY(copy_page)
         addq    $2*8, %rsp
         CFI_ADJUST_CFA_OFFSET -2*8
         ret
-.Lcopy_page_end:
         CFI_ENDPROC
-ENDPROC(copy_page)
-
-        /* Some CPUs run faster using the string copy instructions.
-           It is also a lot simpler. Use this when possible */
-
-#include <asm/cpufeature.h>
-
-        .section .altinstr_replacement,"ax"
-1:      .byte 0xeb                                      /* jmp <disp8> */
-        .byte (copy_page_rep - copy_page) - (2f - 1b)   /* offset */
-2:
-        .previous
-        .section .altinstructions,"a"
-        altinstruction_entry copy_page, 1b, X86_FEATURE_REP_GOOD,       \
-                .Lcopy_page_end-copy_page, 2b-1b, 0
-        .previous
+ENDPROC(copy_page_regs)