target-i386: Fill high bits of mtrr mask

Fill the bits between 51..number-of-physical-address-bits in the
MTRR_PHYSMASKn variable range mtrr masks so that they're consistent
in the migration stream irrespective of the physical address space
of the source VM in a migration.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

include/hw/i386/pc.h

@@ -377,6 +377,11 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = "vmxnet3",\
         .property = "romfile",\
         .value    = "",\
+    },\
+    {\
+        .driver = TYPE_X86_CPU,\
+        .property = "fill-mtrr-mask",\
+        .value = "off",\
     },
 
 #define PC_COMPAT_2_5 \

target-i386/cpu.c

@@ -3328,6 +3328,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
     DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
     DEFINE_PROP_UINT32("phys-bits", X86CPU, phys_bits, 0),
+    DEFINE_PROP_BOOL("fill-mtrr-mask", X86CPU, fill_mtrr_mask, true),
     DEFINE_PROP_UINT32("level", X86CPU, env.cpuid_level, 0),
     DEFINE_PROP_UINT32("xlevel", X86CPU, env.cpuid_xlevel, 0),
     DEFINE_PROP_UINT32("xlevel2", X86CPU, env.cpuid_xlevel2, 0),

target-i386/cpu.h

@@ -1198,6 +1198,9 @@ struct X86CPU {
     /* Compatibility bits for old machine types: */
     bool enable_cpuid_0xb;
 
+    /* if true fill the top bits of the MTRR_PHYSMASKn variable range */
+    bool fill_mtrr_mask;
+
     /* Number of physical address bits supported */
     uint32_t phys_bits;
 

target-i386/kvm.c

@@ -1977,6 +1977,7 @@ static int kvm_get_msrs(X86CPU *cpu)
     CPUX86State *env = &cpu->env;
     struct kvm_msr_entry *msrs = cpu->kvm_msr_buf->entries;
     int ret, i;
+    uint64_t mtrr_top_bits;
 
     kvm_msr_buf_reset(cpu);
 
@@ -2129,6 +2130,30 @@ static int kvm_get_msrs(X86CPU *cpu)
     }
 
     assert(ret == cpu->kvm_msr_buf->nmsrs);
+    /*
+     * MTRR masks: Each mask consists of 5 parts
+     * a  10..0: must be zero
+     * b  11   : valid bit
+     * c n-1.12: actual mask bits
+     * d  51..n: reserved must be zero
+     * e  63.52: reserved must be zero
+     *
+     * 'n' is the number of physical bits supported by the CPU and is
+     * apparently always <= 52.   We know our 'n' but don't know what
+     * the destinations 'n' is; it might be smaller, in which case
+     * it masks (c) on loading. It might be larger, in which case
+     * we fill 'd' so that d..c is consistent irrespetive of the 'n'
+     * we're migrating to.
+     */
+
+    if (cpu->fill_mtrr_mask) {
+        QEMU_BUILD_BUG_ON(TARGET_PHYS_ADDR_SPACE_BITS > 52);
+        assert(cpu->phys_bits <= TARGET_PHYS_ADDR_SPACE_BITS);
+        mtrr_top_bits = MAKE_64BIT_MASK(cpu->phys_bits, 52 - cpu->phys_bits);
+    } else {
+        mtrr_top_bits = 0;
+    }
+
     for (i = 0; i < ret; i++) {
         uint32_t index = msrs[i].index;
         switch (index) {
@@ -2327,7 +2352,8 @@ static int kvm_get_msrs(X86CPU *cpu)
             break;
         case MSR_MTRRphysBase(0) ... MSR_MTRRphysMask(MSR_MTRRcap_VCNT - 1):
             if (index & 1) {
-                env->mtrr_var[MSR_MTRRphysIndex(index)].mask = msrs[i].data;
+                env->mtrr_var[MSR_MTRRphysIndex(index)].mask = msrs[i].data |
+                                                               mtrr_top_bits;
             } else {
                 env->mtrr_var[MSR_MTRRphysIndex(index)].base = msrs[i].data;
             }