[Lucid 2/2 SRU] xen: Allow PV-OPS kernel to detect whether XSAVE is supported

[Stefan Bader]

From: Shan Haitao <haitao.shan at intel.com>

Xen fails to mask XSAVE from the cpuid feature, despite not historically
supporting guest use of XSAVE.  However, now that XSAVE support has been
added to Xen, we need to reliably detect its presence.

The most reliable way to do this is to look at the OSXSAVE feature in
cpuid which is set iff the OS (Xen, in this case), has set
CR4.OSXSAVE.

[ Cleaned up conditional a bit. - Jeremy ]

Signed-off-by: Shan Haitao <haitao.shan at intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>

BugLink: http://bugs.launchpad.net/bugs/1044550

(cherry-picked from commit 947ccf9c3c30307b774af3666ee74fcd9f47f646 upstream)
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 arch/x86/xen/enlighten.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index e66c9ce..2445dd7 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -213,6 +213,7 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 static __init void xen_init_cpuid_mask(void)
 {
 	unsigned int ax, bx, cx, dx;
+	unsigned int xsave_mask;
 
 	cpuid_leaf1_edx_mask =
 		~((1 << X86_FEATURE_MCE)  |  /* disable MCE */
@@ -223,8 +224,16 @@ static __init void xen_init_cpuid_mask(void)
 		cpuid_leaf1_edx_mask &=
 			~((1 << X86_FEATURE_APIC) |  /* disable local APIC */
 			  (1 << X86_FEATURE_ACPI));  /* disable ACPI */
+	ax = 1;
+	xen_cpuid(&ax, &bx, &cx, &dx);
 
-	cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_XSAVE % 32)); /* disable XSAVE */
+	xsave_mask =
+		(1 << (X86_FEATURE_XSAVE % 32)) |
+		(1 << (X86_FEATURE_OSXSAVE % 32));
+
+	/* Xen will set CR4.OSXSAVE if supported and not disabled by force */
+	if ((cx & xsave_mask) != xsave_mask)
+		cpuid_leaf1_ecx_mask &= ~xsave_mask; /* disable XSAVE & OSXSAVE */
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
-- 
1.7.9.5