Commit ced5d0bf authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Ingo Molnar
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x86/entry/64: Use 'xorl' for faster register clearing 



On some x86 CPU microarchitectures using 'xorq' to clear general-purpose
registers is slower than 'xorl'. As 'xorl' is sufficient to clear all
64 bits of these registers due to zero-extension [*], switch the x86
64-bit entry code to use 'xorl'.

No change in functionality and no change in code size.

[*] According to Intel 64 and IA-32 Architecture Software Developer's
    Manual, section 3.4.1.1, the result of 32-bit operands are "zero-
    extended to a 64-bit result in the destination general-purpose
    register." The AMD64 Architecture Programmer’s Manual Volume 3,
    Appendix B.1, describes the same behaviour.

Suggested-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180214175924.23065-3-linux@dominikbrodowski.net


[ Improved on the changelog a bit. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9e809d15

arch/x86/entry/calling.h

+8 −8
Original line number Diff line number Diff line
@@ -117,25 +117,25 @@ For 32-bit we have the following conventions - kernel is built with 
	pushq   %rcx		/* pt_regs->cx */

	pushq   \rax		/* pt_regs->ax */

	pushq   %r8		/* pt_regs->r8 */

	xorq    %r8, %r8	/* nospec   r8 */

	xorl	%r8d, %r8d	/* nospec   r8 */

	pushq   %r9		/* pt_regs->r9 */

	xorq    %r9, %r9	/* nospec   r9 */

	xorl	%r9d, %r9d	/* nospec   r9 */

	pushq   %r10		/* pt_regs->r10 */

	xorq    %r10, %r10	/* nospec   r10 */

	xorl	%r10d, %r10d	/* nospec   r10 */

	pushq   %r11		/* pt_regs->r11 */

	xorq    %r11, %r11	/* nospec   r11*/

	xorl	%r11d, %r11d	/* nospec   r11*/

	pushq	%rbx		/* pt_regs->rbx */

	xorl    %ebx, %ebx	/* nospec   rbx*/

	pushq	%rbp		/* pt_regs->rbp */

	xorl    %ebp, %ebp	/* nospec   rbp*/

	pushq	%r12		/* pt_regs->r12 */

	xorq    %r12, %r12	/* nospec   r12*/

	xorl	%r12d, %r12d	/* nospec   r12*/

	pushq	%r13		/* pt_regs->r13 */

	xorq    %r13, %r13	/* nospec   r13*/

	xorl	%r13d, %r13d	/* nospec   r13*/

	pushq	%r14		/* pt_regs->r14 */

	xorq    %r14, %r14	/* nospec   r14*/

	xorl	%r14d, %r14d	/* nospec   r14*/

	pushq	%r15		/* pt_regs->r15 */

	xorq    %r15, %r15	/* nospec   r15*/

	xorl	%r15d, %r15d	/* nospec   r15*/

	UNWIND_HINT_REGS

	.if \save_ret

	pushq	%rsi		/* return address on top of stack */

arch/x86/entry/entry_64_compat.S

+27 −27
Original line number Diff line number Diff line
@@ -85,25 +85,25 @@ ENTRY(entry_SYSENTER_compat) 
	pushq	%rcx			/* pt_regs->cx */

	pushq	$-ENOSYS		/* pt_regs->ax */

	pushq   $0			/* pt_regs->r8  = 0 */

	xorq	%r8, %r8		/* nospec   r8 */

	xorl	%r8d, %r8d		/* nospec   r8 */

	pushq   $0			/* pt_regs->r9  = 0 */

	xorq	%r9, %r9		/* nospec   r9 */

	xorl	%r9d, %r9d		/* nospec   r9 */

	pushq   $0			/* pt_regs->r10 = 0 */

	xorq	%r10, %r10		/* nospec   r10 */

	xorl	%r10d, %r10d		/* nospec   r10 */

	pushq   $0			/* pt_regs->r11 = 0 */

	xorq	%r11, %r11		/* nospec   r11 */

	xorl	%r11d, %r11d		/* nospec   r11 */

	pushq   %rbx                    /* pt_regs->rbx */

	xorl	%ebx, %ebx		/* nospec   rbx */

	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */

	xorl	%ebp, %ebp		/* nospec   rbp */

	pushq   $0			/* pt_regs->r12 = 0 */

	xorq	%r12, %r12		/* nospec   r12 */

	xorl	%r12d, %r12d		/* nospec   r12 */

	pushq   $0			/* pt_regs->r13 = 0 */

	xorq	%r13, %r13		/* nospec   r13 */

	xorl	%r13d, %r13d		/* nospec   r13 */

	pushq   $0			/* pt_regs->r14 = 0 */

	xorq	%r14, %r14		/* nospec   r14 */

	xorl	%r14d, %r14d		/* nospec   r14 */

	pushq   $0			/* pt_regs->r15 = 0 */

	xorq	%r15, %r15		/* nospec   r15 */

	xorl	%r15d, %r15d		/* nospec   r15 */

	cld



	/*
@@ -224,25 +224,25 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe) 
	pushq	%rbp			/* pt_regs->cx (stashed in bp) */

	pushq	$-ENOSYS		/* pt_regs->ax */

	pushq   $0			/* pt_regs->r8  = 0 */

	xorq	%r8, %r8		/* nospec   r8 */

	xorl	%r8d, %r8d		/* nospec   r8 */

	pushq   $0			/* pt_regs->r9  = 0 */

	xorq	%r9, %r9		/* nospec   r9 */

	xorl	%r9d, %r9d		/* nospec   r9 */

	pushq   $0			/* pt_regs->r10 = 0 */

	xorq	%r10, %r10		/* nospec   r10 */

	xorl	%r10d, %r10d		/* nospec   r10 */

	pushq   $0			/* pt_regs->r11 = 0 */

	xorq	%r11, %r11		/* nospec   r11 */

	xorl	%r11d, %r11d		/* nospec   r11 */

	pushq   %rbx                    /* pt_regs->rbx */

	xorl	%ebx, %ebx		/* nospec   rbx */

	pushq   %rbp                    /* pt_regs->rbp (will be overwritten) */

	xorl	%ebp, %ebp		/* nospec   rbp */

	pushq   $0			/* pt_regs->r12 = 0 */

	xorq	%r12, %r12		/* nospec   r12 */

	xorl	%r12d, %r12d		/* nospec   r12 */

	pushq   $0			/* pt_regs->r13 = 0 */

	xorq	%r13, %r13		/* nospec   r13 */

	xorl	%r13d, %r13d		/* nospec   r13 */

	pushq   $0			/* pt_regs->r14 = 0 */

	xorq	%r14, %r14		/* nospec   r14 */

	xorl	%r14d, %r14d		/* nospec   r14 */

	pushq   $0			/* pt_regs->r15 = 0 */

	xorq	%r15, %r15		/* nospec   r15 */

	xorl	%r15d, %r15d		/* nospec   r15 */



	/*

	 * User mode is traced as though IRQs are on, and SYSENTER
@@ -298,9 +298,9 @@ sysret32_from_system_call: 
	 */

	SWITCH_TO_USER_CR3_NOSTACK scratch_reg=%r8 scratch_reg2=%r9



	xorq	%r8, %r8

	xorq	%r9, %r9

	xorq	%r10, %r10

	xorl	%r8d, %r8d

	xorl	%r9d, %r9d

	xorl	%r10d, %r10d

	swapgs

	sysretl

END(entry_SYSCALL_compat)
@@ -358,25 +358,25 @@ ENTRY(entry_INT80_compat) 
	pushq	%rcx			/* pt_regs->cx */

	pushq	$-ENOSYS		/* pt_regs->ax */

	pushq   $0			/* pt_regs->r8  = 0 */

	xorq	%r8, %r8		/* nospec   r8 */

	xorl	%r8d, %r8d		/* nospec   r8 */

	pushq   $0			/* pt_regs->r9  = 0 */

	xorq	%r9, %r9		/* nospec   r9 */

	xorl	%r9d, %r9d		/* nospec   r9 */

	pushq   $0			/* pt_regs->r10 = 0 */

	xorq	%r10, %r10		/* nospec   r10 */

	xorl	%r10d, %r10d		/* nospec   r10 */

	pushq   $0			/* pt_regs->r11 = 0 */

	xorq	%r11, %r11		/* nospec   r11 */

	xorl	%r11d, %r11d		/* nospec   r11 */

	pushq   %rbx                    /* pt_regs->rbx */

	xorl	%ebx, %ebx		/* nospec   rbx */

	pushq   %rbp                    /* pt_regs->rbp */

	xorl	%ebp, %ebp		/* nospec   rbp */

	pushq   %r12                    /* pt_regs->r12 */

	xorq	%r12, %r12		/* nospec   r12 */

	xorl	%r12d, %r12d		/* nospec   r12 */

	pushq   %r13                    /* pt_regs->r13 */

	xorq	%r13, %r13		/* nospec   r13 */

	xorl	%r13d, %r13d		/* nospec   r13 */

	pushq   %r14                    /* pt_regs->r14 */

	xorq	%r14, %r14		/* nospec   r14 */

	xorl	%r14d, %r14d		/* nospec   r14 */

	pushq   %r15                    /* pt_regs->r15 */

	xorq	%r15, %r15		/* nospec   r15 */

	xorl	%r15d, %r15d		/* nospec   r15 */

	cld



	/*

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