On 05/11/2014 10:03, Tiejun Chen wrote:
> Finally we always return highest_irr so its unnecessary to return -1
> after check if highest_irr == -1.
>
> Signed-off-by: Tiejun Chen <[email protected]>
> ---
> arch/x86/kvm/lapic.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 5f574b4..e6a7eb6 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1638,8 +1638,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
>
> apic_update_ppr(apic);
> highest_irr = apic_find_highest_irr(apic);
> - if ((highest_irr == -1) ||
> - ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)))
> + if ((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI))
> return -1;
> return highest_irr;
> }
I think the code is clearer without this change.
The two returns mean:
- return -1: no interrupt to inject
- return highest_irr: inject this interrupt
With IRR equal to all zeroes (highest_irr = -1), your patch would make
the "if" always false ("current PPR is low, can inject the interrupt"),
but computing highest_irr & 0xF0 would make no sense if highest_irr ==
-1.
To put it another way, imagine the code looked like this:
static inline int int_prio(int vector)
{
WARN_ON(vector == -1);
return vector & 0xF0;
}
...
apic_update_ppr(apic);
highest_irr = apic_find_highest_irr(apic);
if (highest_irr == -1 ||
int_prio(highest_irr) <= kvm_apic_get_reg(apic, APIC_PROCPRI))
return -1;
return highest_irr;
Then removing the check on highest_irr == -1 would trigger a warning.
Paolo
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