[Qemu-devel] [PATCH v4 3/5] x86: Mask mtrr mask based on CPU physical address limits

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

The CPU GPs if we try and set a bit in a variable MTRR mask above
the limit of physical address bits on the host.  We hit this
when loading a migration from a host with a larger physical
address limit than our destination (e.g. a Xeon->i7 of same
generation) but previously used to get away with it
until 48e1a45 started checking that msr writes actually worked.

It seems in our case the GP probably comes from KVM emulating
that GP.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target-i386/kvm.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index f3698f1..6429205 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -1677,6 +1677,8 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
             }
         }
         if (has_msr_mtrr) {
+            uint64_t phys_mask = MAKE_64BIT_MASK(0, cpu->phys_bits);
+
             kvm_msr_entry_add(cpu, MSR_MTRRdefType, env->mtrr_deftype);
             kvm_msr_entry_add(cpu, MSR_MTRRfix64K_00000, env->mtrr_fixed[0]);
             kvm_msr_entry_add(cpu, MSR_MTRRfix16K_80000, env->mtrr_fixed[1]);
@@ -1690,10 +1692,15 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
             kvm_msr_entry_add(cpu, MSR_MTRRfix4K_F0000, env->mtrr_fixed[9]);
             kvm_msr_entry_add(cpu, MSR_MTRRfix4K_F8000, env->mtrr_fixed[10]);
             for (i = 0; i < MSR_MTRRcap_VCNT; i++) {
+                /* The CPU GPs if we write to a bit above the physical limit of
+                 * the host CPU (and KVM emulates that)
+                 */
+                uint64_t mask = env->mtrr_var[i].mask;
+                mask &= phys_mask;
+
                 kvm_msr_entry_add(cpu, MSR_MTRRphysBase(i),
                                   env->mtrr_var[i].base);
-                kvm_msr_entry_add(cpu, MSR_MTRRphysMask(i),
-                                  env->mtrr_var[i].mask);
+                kvm_msr_entry_add(cpu, MSR_MTRRphysMask(i), mask);
             }
         }
 
-- 
2.7.4