From: Ingo Molnar <mingo@kernel.org>
Date: Wed, 8 Apr 2015 07:01:54 +0000 (+0200)
Subject: Merge tag 'v4.0-rc7' into x86/asm, to resolve conflicts
X-Git-Tag: v4.9.8~4513^2~16
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=4bcc7827b02feea2c762fa6d46a1bffb300d7403;p=platform%2Fkernel%2Flinux-rpi3.git

Merge tag 'v4.0-rc7' into x86/asm, to resolve conflicts

Conflicts:
	arch/x86/kernel/entry_64.S

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

4bcc7827b02feea2c762fa6d46a1bffb300d7403
diff --cc arch/x86/kernel/entry_64.S
index f4270ff,f0095a7..65485b3
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@@ -699,14 -792,28 +699,28 @@@ retint_swapgs:		/* return to user-spac
  	shr $__VIRTUAL_MASK_SHIFT, %rcx
  	jnz opportunistic_sysret_failed
  
 -	cmpq $__USER_CS,(CS-R11)(%rsp)		/* CS must match SYSRET */
 +	cmpq $__USER_CS,CS(%rsp)	/* CS must match SYSRET */
  	jne opportunistic_sysret_failed
  
 -	movq (R11-ARGOFFSET)(%rsp), %r11
 -	cmpq %r11,(EFLAGS-ARGOFFSET)(%rsp)	/* R11 == RFLAGS */
 +	movq R11(%rsp),%r11
 +	cmpq %r11,EFLAGS(%rsp)		/* R11 == RFLAGS */
  	jne opportunistic_sysret_failed
  
- 	testq $X86_EFLAGS_RF,%r11	/* sysret can't restore RF */
+ 	/*
+ 	 * SYSRET can't restore RF.  SYSRET can restore TF, but unlike IRET,
+ 	 * restoring TF results in a trap from userspace immediately after
+ 	 * SYSRET.  This would cause an infinite loop whenever #DB happens
+ 	 * with register state that satisfies the opportunistic SYSRET
+ 	 * conditions.  For example, single-stepping this user code:
+ 	 *
+ 	 *           movq $stuck_here,%rcx
+ 	 *           pushfq
+ 	 *           popq %r11
+ 	 *   stuck_here:
+ 	 *
+ 	 * would never get past 'stuck_here'.
+ 	 */
+ 	testq $(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
  	jnz opportunistic_sysret_failed
  
  	/* nothing to check for RSP */