diff options
author | Paul Burton <paul.burton@mips.com> | 2019-03-22 18:04:04 +0000 |
---|---|---|
committer | Paul Burton <paul.burton@mips.com> | 2019-03-25 14:02:12 -0700 |
commit | e6331a321aafcc291a60ceedf4d6b0051a6117ca (patch) | |
tree | 1acdcd75af79d27874f544444c03148528d5121f /arch/mips/kvm/emulate.c | |
parent | 371a415153be953520003ffe4a4eca3fecc0e8c2 (diff) |
MIPS: KVM: Use prandom_u32_max() to generate tlbwr index
Emulation of the tlbwr instruction, which writes a TLB entry to a random
index in the TLB, currently uses get_random_bytes() to generate a 4 byte
random number which we then mask to form the index. This is overkill in
a couple of ways:
- We don't need 4 bytes here since we mask the value to form a 6 bit
number anyway, so we waste /dev/random entropy generating 3 random
bytes that are unused.
- We don't need crypto-grade randomness here - the architecture spec
allows implementations to use any algorithm & merely encourages that
some pseudo-randomness be used rather than a simple counter. The
fast prandom_u32() function fits that criteria well.
So rather than using get_random_bytes() & consuming /dev/random entropy,
switch to using the faster prandom_u32_max() which provides what we need
here whilst also performing the masking/modulo for us.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Reported-by: George Spelvin <lkml@sdf.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Diffstat (limited to 'arch/mips/kvm/emulate.c')
-rw-r--r-- | arch/mips/kvm/emulate.c | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c index 0074427b04fb..e5de6bac8197 100644 --- a/arch/mips/kvm/emulate.c +++ b/arch/mips/kvm/emulate.c @@ -1141,9 +1141,7 @@ enum emulation_result kvm_mips_emul_tlbwr(struct kvm_vcpu *vcpu) unsigned long pc = vcpu->arch.pc; int index; - get_random_bytes(&index, sizeof(index)); - index &= (KVM_MIPS_GUEST_TLB_SIZE - 1); - + index = prandom_u32_max(KVM_MIPS_GUEST_TLB_SIZE); tlb = &vcpu->arch.guest_tlb[index]; kvm_mips_invalidate_guest_tlb(vcpu, tlb); |