On 2014/11/5 18:22, Paolo Bonzini wrote:
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 <tiejun.chen@xxxxxxxxx>
---
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.
Yeah, you're right so here is just a little confusion to read.
Actually what this code is doing looks like,
@@ -1638,7 +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) ||
+ if ((highest_irr != -1) &&
((highest_irr & 0xF0) <= kvm_apic_get_reg(apic, APIC_PROCPRI)))
return -1;
return highest_irr;
But it's really no big deal so we can keep the original alive.
Thanks
Tiejun
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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