Apply alternatives at the call site instead of function body.
Save branch per clean page.
Bonus: tell gcc to not flush whole shebang of registers,
just RDI, RAX, RCX.
Rename individual clear_page() functions closer to implementation
details.
Signed-off-by: Alexey Dobriyan <adobri...@gmail.com>
---
Export individual functions.
arch/x86/include/asm/page_64.h | 16 +++++++++++++++-
arch/x86/kernel/x8664_ksyms_64.c | 4 +++-
arch/x86/lib/clear_page_64.S | 18 ++++++------------
3 files changed, 24 insertions(+), 14 deletions(-)
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -4,6 +4,7 @@
#include <asm/page_64_types.h>
#ifndef __ASSEMBLY__
+#include <asm/alternative.h>
/* duplicated to the one in bootmem.h */
extern unsigned long max_pfn;
@@ -34,7 +35,20 @@ extern unsigned long __phys_addr_symbol(unsigned long);
#define pfn_valid(pfn) ((pfn) < max_pfn)
#endif
-void clear_page(void *page);
+void clear_page_mov(void *page);
+void clear_page_rep_stosq(void *page);
+void clear_page_rep_stosb(void *page);
+static __always_inline void clear_page(void *page)
+{
+ alternative_call_2(
+ clear_page_mov,
+ clear_page_rep_stosq, X86_FEATURE_REP_GOOD,
+ clear_page_rep_stosb, X86_FEATURE_ERMS,
+ "=D" (page),
+ "0" (page)
+ : "rax", "rcx", "memory"
+ );
+}
void copy_page(void *to, void *from);
#endif /* !__ASSEMBLY__ */
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -41,7 +41,9 @@ EXPORT_SYMBOL(_copy_to_user);
EXPORT_SYMBOL_GPL(memcpy_mcsafe);
EXPORT_SYMBOL(copy_page);
-EXPORT_SYMBOL(clear_page);
+EXPORT_SYMBOL(clear_page_mov);
+EXPORT_SYMBOL(clear_page_rep_stosq);
+EXPORT_SYMBOL(clear_page_rep_stosb);
EXPORT_SYMBOL(csum_partial);
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -1,6 +1,4 @@
#include <linux/linkage.h>
-#include <asm/cpufeatures.h>
-#include <asm/alternative-asm.h>
/*
* Most CPUs support enhanced REP MOVSB/STOSB instructions. It is
@@ -13,18 +11,14 @@
* Zero a page.
* %rdi - page
*/
-ENTRY(clear_page)
-
- ALTERNATIVE_2 "jmp clear_page_orig", "", X86_FEATURE_REP_GOOD, \
- "jmp clear_page_c_e", X86_FEATURE_ERMS
-
+ENTRY(clear_page_rep_stosq)
movl $4096/8,%ecx
xorl %eax,%eax
rep stosq
ret
-ENDPROC(clear_page)
+ENDPROC(clear_page_rep_stosq)
-ENTRY(clear_page_orig)
+ENTRY(clear_page_mov)
xorl %eax,%eax
movl $4096/64,%ecx
@@ -44,11 +38,11 @@ ENTRY(clear_page_orig)
jnz .Lloop
nop
ret
-ENDPROC(clear_page_orig)
+ENDPROC(clear_page_mov)
-ENTRY(clear_page_c_e)
+ENTRY(clear_page_rep_stosb)
movl $4096,%ecx
xorl %eax,%eax
rep stosb
ret
-ENDPROC(clear_page_c_e)
+ENDPROC(clear_page_rep_stosb)
