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Commit 8a9949bc authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/xen/64: Rearrange the SYSCALL entries 



Xen's raw SYSCALL entries are much less weird than native.  Rather
than fudging them to look like native entries, use the Xen-provided
stack frame directly.

This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses of
the SWAPGS_UNSAFE_STACK paravirt hook.  The SYSENTER code would
benefit from similar treatment.

This makes one change to the native code path: the compat
instruction that clears the high 32 bits of %rax is moved slightly
later.  I'd be surprised if this affects performance at all.

Tested-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/7c88ed36805d36841ab03ec3b48b4122c4418d71.1502164668.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1d0f49e1

arch/x86/entry/entry_64.S

+2 −7
Original line number Diff line number Diff line
@@ -142,14 +142,8 @@ ENTRY(entry_SYSCALL_64) 
	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,

	 * it is too small to ever cause noticeable irq latency.

	 */

	SWAPGS_UNSAFE_STACK

	/*

	 * A hypervisor implementation might want to use a label

	 * after the swapgs, so that it can do the swapgs

	 * for the guest and jump here on syscall.

	 */

GLOBAL(entry_SYSCALL_64_after_swapgs)



	swapgs

	movq	%rsp, PER_CPU_VAR(rsp_scratch)

	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
@@ -161,6 +155,7 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) 
	pushq	%r11				/* pt_regs->flags */

	pushq	$__USER_CS			/* pt_regs->cs */

	pushq	%rcx				/* pt_regs->ip */

GLOBAL(entry_SYSCALL_64_after_hwframe)

	pushq	%rax				/* pt_regs->orig_ax */

	pushq	%rdi				/* pt_regs->di */

	pushq	%rsi				/* pt_regs->si */

arch/x86/entry/entry_64_compat.S

+3 −4
Original line number Diff line number Diff line
@@ -183,21 +183,20 @@ ENDPROC(entry_SYSENTER_compat) 
 */

ENTRY(entry_SYSCALL_compat)

	/* Interrupts are off on entry. */

	SWAPGS_UNSAFE_STACK

	swapgs



	/* Stash user ESP and switch to the kernel stack. */

	movl	%esp, %r8d

	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp



	/* Zero-extending 32-bit regs, do not remove */

	movl	%eax, %eax



	/* Construct struct pt_regs on stack */

	pushq	$__USER32_DS		/* pt_regs->ss */

	pushq	%r8			/* pt_regs->sp */

	pushq	%r11			/* pt_regs->flags */

	pushq	$__USER32_CS		/* pt_regs->cs */

	pushq	%rcx			/* pt_regs->ip */

GLOBAL(entry_SYSCALL_compat_after_hwframe)

	movl	%eax, %eax		/* discard orig_ax high bits */

	pushq	%rax			/* pt_regs->orig_ax */

	pushq	%rdi			/* pt_regs->di */

	pushq	%rsi			/* pt_regs->si */

arch/x86/xen/xen-asm_64.S

+9 −14
Original line number Diff line number Diff line
@@ -82,34 +82,29 @@ RELOC(xen_sysret64, 1b+1) 
 *	rip

 *	r11

 * rsp->rcx

 *

 * In all the entrypoints, we undo all that to make it look like a

 * CPU-generated syscall/sysenter and jump to the normal entrypoint.

 */



.macro undo_xen_syscall

	mov 0*8(%rsp), %rcx

	mov 1*8(%rsp), %r11

	mov 5*8(%rsp), %rsp

.endm



/* Normal 64-bit system call target */

ENTRY(xen_syscall_target)

	undo_xen_syscall

	jmp entry_SYSCALL_64_after_swapgs

	popq %rcx

	popq %r11

	jmp entry_SYSCALL_64_after_hwframe

ENDPROC(xen_syscall_target)



#ifdef CONFIG_IA32_EMULATION



/* 32-bit compat syscall target */

ENTRY(xen_syscall32_target)

	undo_xen_syscall

	jmp entry_SYSCALL_compat

	popq %rcx

	popq %r11

	jmp entry_SYSCALL_compat_after_hwframe

ENDPROC(xen_syscall32_target)



/* 32-bit compat sysenter target */

ENTRY(xen_sysenter_target)

	undo_xen_syscall

	mov 0*8(%rsp), %rcx

	mov 1*8(%rsp), %r11

	mov 5*8(%rsp), %rsp

	jmp entry_SYSENTER_compat

ENDPROC(xen_sysenter_target)