KVM: MTRR: observe maxphyaddr from guest CPUID, not host

Conversion of MTRRs to ranges used the maxphyaddr from the boot CPU.
This is wrong, because var_mtrr_range's mask variable then is discontiguous
(like FF00FFFF000, where the first run of 0s corresponds to the bits
between host and guest maxphyaddr).  Instead always set up the masks
to be full 64-bit values---we know that the reserved bits at the top
are zero, and we can restore them when reading the MSR.  This way
var_mtrr_range gets a mask that just works.

Fixes: a13842d
Cc: qemu-stable@nongnu.org
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=107561
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mtrr.c

@@ -300,7 +300,6 @@ static void var_mtrr_range(struct kvm_mtrr_range *range, u64 *start, u64 *end)
 	*start = range->base & PAGE_MASK;
 
 	mask = range->mask & PAGE_MASK;
-	mask |= ~0ULL << boot_cpu_data.x86_phys_bits;
 
 	/* This cannot overflow because writing to the reserved bits of
 	 * variable MTRRs causes a #GP.
@@ -356,10 +355,14 @@ static void set_var_mtrr_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 	if (var_mtrr_range_is_valid(cur))
 		list_del(&mtrr_state->var_ranges[index].node);
 
+	/* Extend the mask with all 1 bits to the left, since those
+	 * bits must implicitly be 0.  The bits are then cleared
+	 * when reading them.
+	 */
 	if (!is_mtrr_mask)
 		cur->base = data;
 	else
-		cur->mask = data;
+		cur->mask = data | (-1LL << cpuid_maxphyaddr(vcpu));
 
 	/* add it to the list if it's enabled. */
 	if (var_mtrr_range_is_valid(cur)) {
@@ -426,6 +429,8 @@ int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 			*pdata = vcpu->arch.mtrr_state.var_ranges[index].base;
 		else
 			*pdata = vcpu->arch.mtrr_state.var_ranges[index].mask;
+
+		*pdata &= (1ULL << cpuid_maxphyaddr(vcpu)) - 1;
 	}
 
 	return 0;