linux-kernel - [PATCH 23 of 38] xen-dom0: only selectively disable cpu features

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Message-Id: <fc221c6be28d0aa386d5.1226603421@abulafia.goop.org>
Date:	Thu, 13 Nov 2008 11:10:21 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Ian Campbell <ian.campbell@...rix.com>
Subject: [PATCH 23 of 38] xen-dom0: only selectively disable cpu features

Dom0 kernels actually want most of the CPU features to be enabled.
Some, like MCA/MCE, are still handled by Xen itself.

We leave APIC enabled even though we don't really have a functional
local apic so that the ACPI code will parse the corresponding tables
properly.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 arch/x86/xen/enlighten.c |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -205,18 +205,23 @@
 static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 		      unsigned int *cx, unsigned int *dx)
 {
-	unsigned maskedx = ~0;
+	unsigned maskedx = 0;
 
 	/*
 	 * Mask out inconvenient features, to try and disable as many
 	 * unsupported kernel subsystems as possible.
 	 */
-	if (*ax == 1)
-		maskedx = ~((1 << X86_FEATURE_APIC) |  /* disable APIC */
-			    (1 << X86_FEATURE_ACPI) |  /* disable ACPI */
-			    (1 << X86_FEATURE_MCE)  |  /* disable MCE */
-			    (1 << X86_FEATURE_MCA)  |  /* disable MCA */
-			    (1 << X86_FEATURE_ACC));   /* thermal monitoring */
+	if (*ax == 1) {
+		maskedx =
+			(1 << X86_FEATURE_MCE)  |  /* disable MCE */
+			(1 << X86_FEATURE_MCA)  |  /* disable MCA */
+			(1 << X86_FEATURE_ACC);   /* thermal monitoring */
+
+		if (!xen_initial_domain())
+			maskedx |=
+				(1 << X86_FEATURE_APIC) |  /* disable local APIC */
+				(1 << X86_FEATURE_ACPI);  /* disable ACPI */
+	}
 
 	asm(XEN_EMULATE_PREFIX "cpuid"
 		: "=a" (*ax),
@@ -224,7 +229,7 @@
 		  "=c" (*cx),
 		  "=d" (*dx)
 		: "0" (*ax), "2" (*cx));
-	*dx &= maskedx;
+	*dx &= ~maskedx;
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)


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