linux-kernel - [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V

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Message-Id: <1359940959-32168-2-git-send-email-kys@microsoft.com>
Date:	Sun,  3 Feb 2013 17:22:38 -0800
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	x86@...nel.org, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	olaf@...fle.de, apw@...onical.com, jasowang@...hat.com,
	tglx@...utronix.de, hpa@...or.com, JBeulich@...e.com, bp@...en8.de
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V

Xen emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on Xen.

Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 arch/x86/kernel/cpu/mshyperv.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 646d192..4dab317 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -30,6 +30,13 @@ static bool __init ms_hyperv_platform(void)
 	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		return false;
 
+	/*
+	 * Xen emulates Hyper-V to support enlightened Windows.
+	 * Check to see first if we are on a Xen Hypervisor.
+	 */
+	if (xen_cpuid_base())
+		return false;
+
 	cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
 	      &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);
 
-- 
1.7.4.1

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