target-i386: kvm: Increase MSR_BUF_SIZE

We are dangerously close to the array limits in kvm_put_msrs()
and kvm_get_msrs(): with the default mcg_cap configuration, we
can set up to 148 MSRs in kvm_put_msrs(), and if we allow mcg_cap
to be changed, we can write up to 236 MSRs.

Use 4096 bytes for the buffer, that can hold 255 kvm_msr_entry
structs.
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

target-i386/kvm.c

@@ -57,8 +57,9 @@
 #define MSR_KVM_WALL_CLOCK  0x11
 #define MSR_KVM_SYSTEM_TIME 0x12
 
-#define MSR_BUF_SIZE \
-    (sizeof(struct kvm_msrs) + 150 * sizeof(struct kvm_msr_entry))
+/* A 4096-byte buffer can hold the 8-byte kvm_msrs header, plus
+ * 255 kvm_msr_entry structs */
+#define MSR_BUF_SIZE 4096
 
 #ifndef BUS_MCEERR_AR
 #define BUS_MCEERR_AR 4