linux-kernel - [tip:x86/asm] x86/msr: Set the return value to zero when native_rdmsr

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Message-ID: <tip-b828b79fcced0e66492590707649dbfaea6435e6@git.kernel.org>
Date:	Wed, 13 Apr 2016 04:46:29 -0700
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, hpa@...or.com, mingo@...nel.org,
	akpm@...ux-foundation.org, kvm@...r.kernel.org,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	boris.ostrovsky@...cle.com, arjan@...ux.intel.com, luto@...nel.org,
	bp@...en8.de, Xen-devel@...ts.xen.org,
	torvalds@...ux-foundation.org, pbonzini@...hat.com
Subject: [tip:x86/asm] x86/msr: Set the return value to zero when
 native_rdmsr_safe() fails

Commit-ID:  b828b79fcced0e66492590707649dbfaea6435e6
Gitweb:     http://git.kernel.org/tip/b828b79fcced0e66492590707649dbfaea6435e6
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Sat, 2 Apr 2016 07:01:40 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 13 Apr 2016 11:37:46 +0200

x86/msr: Set the return value to zero when native_rdmsr_safe() fails

This will cause unchecked native_rdmsr_safe() failures to return
deterministic results.

Tested-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: KVM list <kvm@...r.kernel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: xen-devel <Xen-devel@...ts.xen.org>
Link: http://lkml.kernel.org/r/515fb611449a755312a476cfe11675906e7ddf6c.1459605520.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/msr.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 00050c0..7dc1d8f 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -101,7 +101,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
 	asm volatile("2: rdmsr ; xor %[err],%[err]\n"
 		     "1:\n\t"
 		     ".section .fixup,\"ax\"\n\t"
-		     "3:  mov %[fault],%[err] ; jmp 1b\n\t"
+		     "3: mov %[fault],%[err]\n\t"
+		     "xorl %%eax, %%eax\n\t"
+		     "xorl %%edx, %%edx\n\t"
+		     "jmp 1b\n\t"
 		     ".previous\n\t"
 		     _ASM_EXTABLE(2b, 3b)
 		     : [err] "=r" (*err), EAX_EDX_RET(val, low, high)