[Xen-devel] [PATCH] xen: allow HVM save/restore from different cpus

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

The hardware CPUID-levelling features level the feature flags but don't
change the CPU family/model/stepping.  Relax the HVM restore check on 
family/model/stepping to printk but not veto the load, so that VMs can 
be migrated between machines that have been CPUID-levelled.  

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>

diff -r 281896d3343a xen/arch/x86/hvm/save.c
--- a/xen/arch/x86/hvm/save.c   Thu Jul 08 12:07:16 2010 +0100
+++ b/xen/arch/x86/hvm/save.c   Thu Jul 08 12:10:59 2010 +0100
@@ -55,10 +55,11 @@
     }
 
     cpuid(1, &eax, &ebx, &ecx, &edx);
-    /* TODO: need to define how big a difference is acceptable? */
-    if ( hdr->cpuid != eax )
-        gdprintk(XENLOG_WARNING, "HVM restore: saved CPUID (%#"PRIx32") "
-               "does not match host (%#"PRIx32").\n", hdr->cpuid, eax);
+    /* CPUs ought to match but with feature-masking they might not */
+    if ( (hdr->cpuid & ~0x0fUL) != (eax & ~0x0fUL) )
+        gdprintk(XENLOG_INFO, "HVM restore (%u): VM saved on one CPU "
+                 "(%#"PRIx32") and restored on another (%#"PRIx32").\n", 
+                 d->domain_id, hdr->cpuid, eax);
 
     /* Restore guest's preferred TSC frequency. */
     if ( hdr->gtsc_khz )

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