On 07/06/2019 09:35, Julien Thierry wrote:
> Hi Marc,
>
> On 06/06/2019 17:54, Marc Zyngier wrote:
>> On a successful translation, preserve the parameters in the LPI
>> translation cache. Each translation is reusing the last slot
>> in the list, naturally evincting the least recently used entry.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>> virt/kvm/arm/vgic/vgic-its.c | 41 ++++++++++++++++++++++++++++++++++++
>> 1 file changed, 41 insertions(+)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 5758504fd934..bc370b6c5afa 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -538,6 +538,45 @@ static unsigned long vgic_mmio_read_its_idregs(struct kvm *kvm,
>> return 0;
>> }
>>
>> +static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
>> + u32 devid, u32 eventid,
>> + struct vgic_irq *irq)
>> +{
>> + struct vgic_dist *dist = &kvm->arch.vgic;
>> + struct vgic_translation_cache_entry *cte;
>> + unsigned long flags;
>> +
>> + /* Do not cache a directly injected interrupt */
>> + if (irq->hw)
>> + return;
>> +
>> + raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
>> +
>> + /* Always reuse the last entry (LRU policy) */
>> + cte = list_last_entry(&dist->lpi_translation_cache,
>> + typeof(*cte), entry);
>> +
>> + /*
>> + * Caching the translation implies having an extra reference
>> + * to the interrupt, so drop the potential reference on what
>> + * was in the cache, and increment it on the new interrupt.
>> + */
>> + if (cte->irq)
>> + __vgic_put_lpi_locked(kvm, cte->irq);
>> +
>> + vgic_get_irq_kref(irq);
>
> If cte->irq == irq, can we avoid the ref putting and getting and just
> move the list entry (and update cte)?
But in that case, we should have hit in the cache the first place, no?
Or is there a particular race I'm not thinking of just yet?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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