KVM: MIPS: Fix maybe-uninitialized build failure

This commit fixes a "maybe-uninitialized" build failure in
arch/mips/kvm/tlb.c when KVM, DYNAMIC_DEBUG and JUMP_LABEL are all
enabled. The failure is:

In file included from ./include/linux/printk.h:329:0,
                 from ./include/linux/kernel.h:13,
                 from ./include/asm-generic/bug.h:15,
                 from ./arch/mips/include/asm/bug.h:41,
                 from ./include/linux/bug.h:4,
                 from ./include/linux/thread_info.h:11,
                 from ./include/asm-generic/current.h:4,
                 from ./arch/mips/include/generated/asm/current.h:1,
                 from ./include/linux/sched.h:11,
                 from arch/mips/kvm/tlb.c:13:
arch/mips/kvm/tlb.c: In function ‘kvm_mips_host_tlb_inv’:
./include/linux/dynamic_debug.h:126:3: error: ‘idx_kernel’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
   __dynamic_pr_debug(&descriptor, pr_fmt(fmt), \
   ^~~~~~~~~~~~~~~~~~
arch/mips/kvm/tlb.c:169:16: note: ‘idx_kernel’ was declared here
  int idx_user, idx_kernel;
                ^~~~~~~~~~

There is a similar error relating to "idx_user". Both errors were
observed with GCC 6.

As far as I can tell, it is impossible for either idx_user or idx_kernel
to be uninitialized when they are later read in the calls to kvm_debug,
but to satisfy the compiler, add zero initializers to both variables.

Signed-off-by: James Cowgill <[email protected]>
Fixes: 57e3869 ("KVM: MIPS/TLB: Generalise host TLB invalidate to kernel ASID")
Cc: <[email protected]> # 4.11+
Acked-by: James Hogan <[email protected]>
Signed-off-by: Radim Krčmář <[email protected]>

arch/mips/kvm/tlb.c

@@ -166,7 +166,11 @@ static int _kvm_mips_host_tlb_inv(unsigned long entryhi)
 int kvm_mips_host_tlb_inv(struct kvm_vcpu *vcpu, unsigned long va,
 			  bool user, bool kernel)
 {
-	int idx_user, idx_kernel;
+	/*
+	 * Initialize idx_user and idx_kernel to workaround bogus
+	 * maybe-initialized warning when using GCC 6.
+	 */
+	int idx_user = 0, idx_kernel = 0;
 	unsigned long flags, old_entryhi;
 
 	local_irq_save(flags);