Re: [PATCH 2/2] x86/entry/64: use xorl for register clearing

All of lore.kernel.org
 help / color / mirror / Atom feed

* Re: [PATCH 2/2] x86/entry/64: use xorl for register clearing
@ 2018-02-14 18:21 Alexey Dobriyan
  2018-02-14 18:27 ` Dominik Brodowski
  0 siblings, 1 reply; 3+ messages in thread
From: Alexey Dobriyan @ 2018-02-14 18:21 UTC (permalink / raw)
  To: linux; +Cc: linux-kernel

> -	xorq    %r8, %r8	/* nospec   r8 */
> +	xorl	%r8d, %r8d	/* nospec   r8 */

The suffix should be simply dropped as operand size is unambigious.
It is just one more character than necessary on the screen.

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH 2/2] x86/entry/64: use xorl for register clearing
  2018-02-14 18:21 [PATCH 2/2] x86/entry/64: use xorl for register clearing Alexey Dobriyan
@ 2018-02-14 18:27 ` Dominik Brodowski
  0 siblings, 0 replies; 3+ messages in thread
From: Dominik Brodowski @ 2018-02-14 18:27 UTC (permalink / raw)
  To: Alexey Dobriyan; +Cc: linux-kernel

On Wed, Feb 14, 2018 at 09:21:12PM +0300, Alexey Dobriyan wrote:
> > -	xorq    %r8, %r8	/* nospec   r8 */
> > +	xorl	%r8d, %r8d	/* nospec   r8 */
> 
> The suffix should be simply dropped as operand size is unambigious.
> It is just one more character than necessary on the screen.

No strong feelings about this issue, but I prefer it to be explicit. And
that's what seems to be the standard in arch/x86/entry/ .

Thanks,
	Dominik

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [PATCH 0/2] x86/entry: xorq->xorl; idtentry size reduction
@ 2018-02-14 17:59 Dominik Brodowski
  2018-02-14 17:59 ` [PATCH 2/2] x86/entry/64: use xorl for register clearing Dominik Brodowski
  0 siblings, 1 reply; 3+ messages in thread
From: Dominik Brodowski @ 2018-02-14 17:59 UTC (permalink / raw)
  To: linux-kernel, mingo, x86, torvalds; +Cc: luto, ak, tglx, dan.j.williams

These two patches apply on top of tip/pti.

The first one cuts the idtentry macro as suggested by Linus.
I'm not sure whether this patch yet needs an explicit SOB by
him though. It was previously sent as RFC / testing only patch
"8/7" to the previous x86/entry-related series, cf.
http://lkml.kernel.org/r/20180211104949.12992-9-linux@dominikbrodowski.net

The other one replaces the xorq-based register cleaning with an
equivalent xorl-based version, which is supposed to be faster on
some architectures.

Thanks,
	Dominik

Dominik Brodowski (2):
  x86/entry: reduce static footprint of idtentry
  x86/entry/64: use xorl for register clearing

 arch/x86/entry/calling.h         | 27 +++++++++++++-------
 arch/x86/entry/entry_64.S        | 18 ++++++--------
 arch/x86/entry/entry_64_compat.S | 54 ++++++++++++++++++++--------------------
 3 files changed, 53 insertions(+), 46 deletions(-)

-- 
2.16.1

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [PATCH 2/2] x86/entry/64: use xorl for register clearing
  2018-02-14 17:59 [PATCH 0/2] x86/entry: xorq->xorl; idtentry size reduction Dominik Brodowski
@ 2018-02-14 17:59 ` Dominik Brodowski
  0 siblings, 0 replies; 3+ messages in thread
From: Dominik Brodowski @ 2018-02-14 17:59 UTC (permalink / raw)
  To: linux-kernel, mingo, x86, torvalds; +Cc: luto, ak, tglx, dan.j.williams

Using xorq to clear general-purpose registers is slower than
xorl on some architectures. As xorl is sufficient to clear all
64bit of these registers,[*] switch the x86 64-bit entry code
to use xorl.

[*] 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: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
 arch/x86/entry/calling.h         | 16 ++++++------
 arch/x86/entry/entry_64_compat.S | 54 ++++++++++++++++++++--------------------
 2 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 79ead48e6fe1..adaf5fd9840d 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -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 */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index fd65e016e413..364ea4a207be 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -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
 
 	/*
-- 
2.16.1

^ permalink raw reply related	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2018-02-14 18:27 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-02-14 18:21 [PATCH 2/2] x86/entry/64: use xorl for register clearing Alexey Dobriyan
2018-02-14 18:27 ` Dominik Brodowski
  -- strict thread matches above, loose matches on Subject: below --
2018-02-14 17:59 [PATCH 0/2] x86/entry: xorq->xorl; idtentry size reduction Dominik Brodowski
2018-02-14 17:59 ` [PATCH 2/2] x86/entry/64: use xorl for register clearing Dominik Brodowski

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.