MIPS: KVM: Move commpage so 0x0 is unmapped

[deliverable/linux.git] / arch / mips / include / asm / kvm_host.h

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 5e9da2a31fde028a40548555c324e2efe4e7bf51..6c43c782bdfad17762e903c25ccca1fe2059e31b 100644 (file)
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -74,8 +74,14 @@
 
 
 
-/* Special address that contains the comm page, used for reducing # of traps */
-#define KVM_GUEST_COMMPAGE_ADDR                0x0
+/*
+ * Special address that contains the comm page, used for reducing # of traps
+ * This needs to be within 32Kb of 0x0 (so the zero register can be used), but
+ * preferably not at 0x0 so that most kernel NULL pointer dereferences can be
+ * caught.
+ */
+#define KVM_GUEST_COMMPAGE_ADDR                ((PAGE_SIZE > 0x8000) ? 0 : \
+                                        (0x8000 - PAGE_SIZE))
 
 #define KVM_GUEST_KERNEL_MODE(vcpu)    ((kvm_read_c0_guest_status(vcpu->arch.cop0) & (ST0_EXL | ST0_ERL)) || \
                                        ((kvm_read_c0_guest_status(vcpu->arch.cop0) & KSU_USER) == 0))