From 6620ef28c812b4782b10adb676580c2847d2bec8 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Sun, 18 Jan 2015 12:57:41 +0100 Subject: [PATCH] x86/lib/clear_page_64.S: Convert to ALTERNATIVE_2 macro Move clear_page() up so that we can get 2-byte forward JMPs when patching: apply_alternatives: feat: 3*32+16, old: (ffffffff8130adb0, len: 5), repl: (ffffffff81d0b859, len: 5) ffffffff8130adb0: alt_insn: 90 90 90 90 90 recompute_jump: new_displ: 0x0000003e ffffffff81d0b859: rpl_insn: eb 3e 66 66 90 even though the compiler generated 5-byte JMPs which we padded with 5 NOPs. Also, make the REP_GOOD version be the default as the majority of machines set REP_GOOD. This way we get to save ourselves the JMP: old insn VA: 0xffffffff813038b0, CPU feat: X86_FEATURE_REP_GOOD, size: 5, padlen: 0 clear_page: ffffffff813038b0 : ffffffff813038b0: e9 0b 00 00 00 jmpq ffffffff813038c0 repl insn: 0xffffffff81cf0e92, size: 0 old insn VA: 0xffffffff813038b0, CPU feat: X86_FEATURE_ERMS, size: 5, padlen: 0 clear_page: ffffffff813038b0 : ffffffff813038b0: e9 0b 00 00 00 jmpq ffffffff813038c0 repl insn: 0xffffffff81cf0e92, size: 5 ffffffff81cf0e92: e9 69 2a 61 ff jmpq ffffffff81303900 ffffffff813038b0 : ffffffff813038b0: e9 69 2a 61 ff jmpq ffffffff8091631e Signed-off-by: Borislav Petkov --- arch/x86/lib/clear_page_64.S | 66 +++++++++++++++--------------------- 1 file changed, 27 insertions(+), 39 deletions(-) diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S index 38e57faefd71..e67e579c93bd 100644 --- a/arch/x86/lib/clear_page_64.S +++ b/arch/x86/lib/clear_page_64.S @@ -1,31 +1,35 @@ #include #include +#include #include /* - * Zero a page. - * rdi page - */ -ENTRY(clear_page_c) + * Most CPUs support enhanced REP MOVSB/STOSB instructions. It is + * recommended to use this when possible and we do use them by default. + * If enhanced REP MOVSB/STOSB is not available, try to use fast string. + * Otherwise, use original. + */ + +/* + * Zero a page. + * %rdi - page + */ +ENTRY(clear_page) CFI_STARTPROC + + ALTERNATIVE_2 "jmp clear_page_orig", "", X86_FEATURE_REP_GOOD, \ + "jmp clear_page_c_e", X86_FEATURE_ERMS + movl $4096/8,%ecx xorl %eax,%eax rep stosq ret CFI_ENDPROC -ENDPROC(clear_page_c) +ENDPROC(clear_page) -ENTRY(clear_page_c_e) +ENTRY(clear_page_orig) CFI_STARTPROC - movl $4096,%ecx - xorl %eax,%eax - rep stosb - ret - CFI_ENDPROC -ENDPROC(clear_page_c_e) -ENTRY(clear_page) - CFI_STARTPROC xorl %eax,%eax movl $4096/64,%ecx .p2align 4 @@ -45,29 +49,13 @@ ENTRY(clear_page) nop ret CFI_ENDPROC -.Lclear_page_end: -ENDPROC(clear_page) - - /* - * Some CPUs support enhanced REP MOVSB/STOSB instructions. - * It is recommended to use this when possible. - * If enhanced REP MOVSB/STOSB is not available, try to use fast string. - * Otherwise, use original function. - * - */ +ENDPROC(clear_page_orig) -#include - - .section .altinstr_replacement,"ax" -1: .byte 0xeb /* jmp */ - .byte (clear_page_c - clear_page) - (2f - 1b) /* offset */ -2: .byte 0xeb /* jmp */ - .byte (clear_page_c_e - clear_page) - (3f - 2b) /* offset */ -3: - .previous - .section .altinstructions,"a" - altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\ - .Lclear_page_end-clear_page, 2b-1b, 0 - altinstruction_entry clear_page,2b,X86_FEATURE_ERMS, \ - .Lclear_page_end-clear_page,3b-2b, 0 - .previous +ENTRY(clear_page_c_e) + CFI_STARTPROC + movl $4096,%ecx + xorl %eax,%eax + rep stosb + ret + CFI_ENDPROC +ENDPROC(clear_page_c_e) -- 2.20.1