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[Xen-devel] [PATCH] libxc: set CPUID topology leaf as unsupported for PV

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH] libxc: set CPUID topology leaf as unsupported for PV guests
From: David Vrabel <david.vrabel@xxxxxxxxxx>
Date: Thu, 14 Jul 2011 12:50:19 +0100
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
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# HG changeset patch
# User David Vrabel <david.vrabel@xxxxxxxxxx>
# Date 1310643124 -3600
# Branch cpuid
# Node ID b3705aae543b95fd7f6bb38c21b5f1edd2b70609
# Parent  98701b1276c034b2bbbc8c7a975cf4c361caaa63
libxc: set CPUID topology leaf as unsupported for PV guests

The result of a CPUID Extended Topology Enumeration leaf for PV guests
is invalid as the level in ECX is ignored.  This can cause some guests
to loop endlessly when trying to enumerate the topology.

Since the physical topology isn't useful to PV guests set the topology
leaf as unsupported.

Guests affected include Linux kernels prior 2.6.32 where a workaround
was applied ("xen: mask extended topology info in cpu",

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

diff -r 98701b1276c0 -r b3705aae543b tools/libxc/xc_cpuid_x86.c
--- a/tools/libxc/xc_cpuid_x86.c        Thu Jul 14 09:43:37 2011 +0100
+++ b/tools/libxc/xc_cpuid_x86.c        Thu Jul 14 12:32:04 2011 +0100
@@ -487,6 +487,11 @@ static void xc_cpuid_pv_policy(
         regs[0] = regs[2] = regs[3] = 0;
+    case 0x0000000b:
+        /* Extended Topology Enumeration leaf is unsupported. */
+        regs[0] = regs[1] = regs[2] = regs[3] = 0;
+        break;
     case 0x0000000d:
         xc_cpuid_config_xsave(xch, domid, xfeature_mask, input, regs);

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