On 09/12/2016 08:02, Liang Li wrote:
> Use '||' is more efficient than '|' at this point.
No, it's not, because the check is going to be always false in practice,
so the || is going to evaluate both branches anyway. So, depending on
the compiler, either it's the same or it's worse (because a branch is
worse than an OR instruction).
If anything, as David said (and if the compiled code changes at all),
the "!= 0" is superfluous.
Paolo
> Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index d9c7e98..16c0b00 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3315,7 +3315,7 @@ static gpa_t nonpaging_gva_to_gpa_nested(struct kvm_vcpu *vcpu, gva_t vaddr,
> {
> int bit7 = (pte >> 7) & 1, low6 = pte & 0x3f;
>
> - return (pte & rsvd_check->rsvd_bits_mask[bit7][level-1]) |
> + return (pte & rsvd_check->rsvd_bits_mask[bit7][level-1]) ||
> ((rsvd_check->bad_mt_xwr & (1ull << low6)) != 0);
> }
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