Re: [PATCH 4.19 17/32] iommu/vt-d: Dont queue_iova() if there is no flush queue

Pavel Machek
2019-08-03T21:34:59Z

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Hi!

> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -3721,7 +3721,7 @@ static void intel_unmap(struct device *d
>
> freelist = domain_unmap(domain, start_pfn, last_pfn);
>
> - if (intel_iommu_strict) {
> + if (intel_iommu_strict || !has_iova_flush_queue(&domain->iovad)) {
> iommu_flush_iotlb_psi(iommu, domain, start_pfn,
> nrpages, !freelist, 0);
> /* free iova */
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -65,9 +65,14 @@ init_iova_domain(struct iova_domain *iov
> }
> EXPORT_SYMBOL_GPL(init_iova_domain);
>
> +bool has_iova_flush_queue(struct iova_domain *iovad)
> +{
> + return !!iovad->fq;

Should this be READ_ONCE()?

> @@ -100,13 +106,17 @@ int init_iova_flush_queue(struct iova_do
> for_each_possible_cpu(cpu) {
> struct iova_fq *fq;
>
> - fq = per_cpu_ptr(iovad->fq, cpu);
> + fq = per_cpu_ptr(queue, cpu);
> fq->head = 0;
> fq->tail = 0;
>
> spin_lock_init(&fq->lock);
> }
>
> + smp_wmb();
> +
> + iovad->fq = queue;
> +

Could we have a comment why the barrier is needed, and perhaps there
should be oposing smp_rmb() somewhere? Does this need to be
WRITE_ONCE() as it is racing against reader?

Thanks,
Pavel

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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