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/* SPDX-License-Identifier: GPL-2.0-only */
#include <linux/export.h>
#include <linux/linkage.h>
#include <asm/asm.h>
/*
* 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
*/
SYM_FUNC_START(clear_page_rep)
movl $4096/8,%ecx
xorl %eax,%eax
rep stosq
RET
SYM_FUNC_END(clear_page_rep)
EXPORT_SYMBOL_GPL(clear_page_rep)
SYM_FUNC_START(clear_page_orig)
xorl %eax,%eax
movl $4096/64,%ecx
.p2align 4
.Lloop:
decl %ecx
#define PUT(x) movq %rax,x*8(%rdi)
movq %rax,(%rdi)
PUT(1)
PUT(2)
PUT(3)
PUT(4)
PUT(5)
PUT(6)
PUT(7)
leaq 64(%rdi),%rdi
jnz .Lloop
nop
RET
SYM_FUNC_END(clear_page_orig)
EXPORT_SYMBOL_GPL(clear_page_orig)
SYM_FUNC_START(clear_page_erms)
movl $4096,%ecx
xorl %eax,%eax
rep stosb
RET
SYM_FUNC_END(clear_page_erms)
EXPORT_SYMBOL_GPL(clear_page_erms)
/*
* Default clear user-space.
* Input:
* rdi destination
* rcx count
* rax is zero
*
* Output:
* rcx: uncleared bytes or 0 if successful.
*/
SYM_FUNC_START(rep_stos_alternative)
cmpq $64,%rcx
jae .Lunrolled
cmp $8,%ecx
jae .Lword
testl %ecx,%ecx
je .Lexit
.Lclear_user_tail:
0: movb %al,(%rdi)
inc %rdi
dec %rcx
jnz .Lclear_user_tail
.Lexit:
RET
_ASM_EXTABLE_UA( 0b, .Lexit)
.Lword:
1: movq %rax,(%rdi)
addq $8,%rdi
sub $8,%ecx
je .Lexit
cmp $8,%ecx
jae .Lword
jmp .Lclear_user_tail
.p2align 4
.Lunrolled:
10: movq %rax,(%rdi)
11: movq %rax,8(%rdi)
12: movq %rax,16(%rdi)
13: movq %rax,24(%rdi)
14: movq %rax,32(%rdi)
15: movq %rax,40(%rdi)
16: movq %rax,48(%rdi)
17: movq %rax,56(%rdi)
addq $64,%rdi
subq $64,%rcx
cmpq $64,%rcx
jae .Lunrolled
cmpl $8,%ecx
jae .Lword
testl %ecx,%ecx
jne .Lclear_user_tail
RET
/*
* If we take an exception on any of the
* word stores, we know that %rcx isn't zero,
* so we can just go to the tail clearing to
* get the exact count.
*
* The unrolled case might end up clearing
* some bytes twice. Don't care.
*
* We could use the value in %rdi to avoid
* a second fault on the exact count case,
* but do we really care? No.
*
* Finally, we could try to align %rdi at the
* top of the unrolling. But unaligned stores
* just aren't that common or expensive.
*/
_ASM_EXTABLE_UA( 1b, .Lclear_user_tail)
_ASM_EXTABLE_UA(10b, .Lclear_user_tail)
_ASM_EXTABLE_UA(11b, .Lclear_user_tail)
_ASM_EXTABLE_UA(12b, .Lclear_user_tail)
_ASM_EXTABLE_UA(13b, .Lclear_user_tail)
_ASM_EXTABLE_UA(14b, .Lclear_user_tail)
_ASM_EXTABLE_UA(15b, .Lclear_user_tail)
_ASM_EXTABLE_UA(16b, .Lclear_user_tail)
_ASM_EXTABLE_UA(17b, .Lclear_user_tail)
SYM_FUNC_END(rep_stos_alternative)
EXPORT_SYMBOL(rep_stos_alternative)
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