From: Andrew Jones <drjones@redhat.com>
Date: Wed, 18 Nov 2009 15:36:50 -0500
Subject: [xen] mask extended topo cpuid feature
Message-id: <5919d717c4960323fc20f9e5de802c784ba744ee.1258558545.git.drjones@redhat.com>
Patchwork-id: 21417
O-Subject: [RHEL5.5 PATCH] [xen] mask extended topo cpuid feature
Bugzilla: 533292
RH-Acked-by: Anton Arapov <Anton@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Christopher Lalancette <clalance@redhat.com>

The extended topo cpu feature is not supported for Xen hosted guests. If
the guest attempts to use ext. topo, then it may fail to boot. Upstream
half-way emulates this by returning a vcpu id in edx, but still only zero
for the extended topology information (ebx). This patch returns zero for
all registers to avoid confusing the guest. It also takes the added
precaution of always stating the max cpuid input as <= 0xa. Features > 0xa,
for example 0xb: ext. topo are not supported, so the max input should not
state it as such. This patch resolves bz 533292.

Tested by me by booting a guest and running 'x86info -r'. A subset of this
patch, the returning of zero for the cpuid 0xb, was tested on a system that
failed to boot. The patch allowed the system to boot.

Brew build: https://brewweb.devel.redhat.com/taskinfo?taskID=2082312

---
 arch/x86/hvm/vmx/vmx.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/x86/hvm/vmx/vmx.c b/arch/x86/hvm/vmx/vmx.c
index ce8da33..d5b6002 100644
--- a/arch/x86/hvm/vmx/vmx.c
+++ b/arch/x86/hvm/vmx/vmx.c
@@ -1599,6 +1599,10 @@ static void vmx_do_cpuid(struct cpu_user_regs *regs)
     } else {
         hvm_cpuid(input, &eax, &ebx, &ecx, &edx);
 
+	/* don't support features > 0xa */
+	if (unlikely(input == 0x0) && eax > 0xa)
+		eax = 0xa;
+
         if ( input == 0x00000001 )
         {
             /* Mask off reserved bits. */
@@ -1619,7 +1623,8 @@ static void vmx_do_cpuid(struct cpu_user_regs *regs)
                      bitmaskof(X86_FEATURE_ACC));
         }
 
-        if ( input == 0x00000006 || input == 0x00000009 || input == 0x0000000A )
+        if ( input == 0x00000006 || input == 0x00000009 ||
+		input == 0x0000000A || input == 0x0000000B )
             eax = ebx = ecx = edx = 0x0;
     }