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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/x86/lib/clear_page_64.S
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#include <linux/linkage.h>

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#include <asm/dwarf2.h>

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#include <asm/alternative-asm.h>

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/*

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 * Zero a page. 	

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 * rdi	page

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 */			

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ENTRY(clear_page_c)

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	CFI_STARTPROC

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	movl $4096/8,%ecx

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	xorl %eax,%eax

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	rep stosq

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	ret

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	CFI_ENDPROC

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ENDPROC(clear_page_c)

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ENTRY(clear_page_c_e)

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	CFI_STARTPROC

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	movl $4096,%ecx

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	xorl %eax,%eax

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	rep stosb

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	ret

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	CFI_ENDPROC

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ENDPROC(clear_page_c_e)

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ENTRY(clear_page)

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	CFI_STARTPROC

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	xorl   %eax,%eax

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	movl   $4096/64,%ecx

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	.p2align 4

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.Lloop:

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	decl	%ecx

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#define PUT(x) movq %rax,x*8(%rdi)

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	movq %rax,(%rdi)

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	PUT(1)

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	PUT(2)

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	PUT(3)

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	PUT(4)

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	PUT(5)

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	PUT(6)

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	PUT(7)

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	leaq	64(%rdi),%rdi

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	jnz	.Lloop

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	nop

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	ret

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	CFI_ENDPROC

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.Lclear_page_end:

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ENDPROC(clear_page)

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	/*

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	 * Some CPUs support enhanced REP MOVSB/STOSB instructions.

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	 * It is recommended to use this when possible.

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	 * If enhanced REP MOVSB/STOSB is not available, try to use fast string.

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	 * Otherwise, use original function.

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	 *

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	 */

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#include <asm/cpufeature.h>

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	.section .altinstr_replacement,"ax"

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1:	.byte 0xeb					/* jmp <disp8> */

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	.byte (clear_page_c - clear_page) - (2f - 1b)	/* offset */

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2:	.byte 0xeb					/* jmp <disp8> */

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	.byte (clear_page_c_e - clear_page) - (3f - 2b)	/* offset */

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3:

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	.previous

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	.section .altinstructions,"a"

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	altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\

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			     .Lclear_page_end-clear_page, 2b-1b

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	altinstruction_entry clear_page,2b,X86_FEATURE_ERMS,   \

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			     .Lclear_page_end-clear_page,3b-2b

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	.previous

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