[PATCH] arch/mips/kvm/emulate.c: Don't waste /dev/random emulating TLBWR

[George Spelvin <lkml@sdf.org>]

KVM_MIPS_GUEST_TLB_SIZE is 64, so we only need one random byte,
not 4.

A more complex question is whether we need crypto-grade random
numbers at all.  If safe, we could use prandom_u32().  If not,
we could seed a private PRNG and use prandom_u32_state().

Or could we just use asm("mfc0 %0, Random" : "=r" (index))?

Signed-off-by: George Spelvin <lkml@sdf.org>
---
I ran across this whie doing some other cleanups, and thought
I'd pass it on.

get_random_bytes() is quite an expensive function call.
Is it needed at all?

 arch/mips/kvm/emulate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index ec9ed23bca7f..a689f3db3094 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -1139,8 +1139,9 @@ enum emulation_result kvm_mips_emul_tlbwr(struct kvm_vcpu *vcpu)
 	struct mips_coproc *cop0 = vcpu->arch.cop0;
 	struct kvm_mips_tlb *tlb = NULL;
 	unsigned long pc = vcpu->arch.pc;
-	int index;
+	unsigned char index;
 
+	/* Do we need this quality of random numbers?  Would prandom_u32 do? */
 	get_random_bytes(&index, sizeof(index));
 	index &= (KVM_MIPS_GUEST_TLB_SIZE - 1);
 
-- 
2.20.1