Re: [PATCH] iommu/dma: Fix race condition during iova_domain initialization

[Miles Chen]

Hi YF,

>When many devices share the same iova domain, iommu_dma_init_domain()
>may be called at the same time. The checking of iovad->start_pfn will
>all get false in iommu_dma_init_domain() and both enter init_iova_domain()
>to do iovad initialization.

After reading this patch.
It means that we use iovad->start_pfn as a key to tell if an iovad is already initialized,
but we do not protect iovad->start_pfn from concurrent access.

So what's happening is like:

   cpu0                                    cpu1
of_dma_configure_id()              of_dma_configure_id()
  arch_setup_dma_ops()               arch_setup_dma_ops()
    iommu_setup_dma_ops()              iommu_setup_dma_ops()
      init_iova_domain()	 	 init_iova_domain()
         if (iovad->start_pfn) {           if (iovad->start_pfn) {
         }                                 }
         init_iova_domain()                init_iova_domain()


init_iova_domain() is called at the same time.

>Fix this by protecting init_iova_domain() with iommu_dma_cookie->mutex.

Reviewed-by: Miles Chen <miles.chen@xxxxxxxxxxxx> 

>Exception backtrace:
>rb_insert_color(param1=0xFFFFFF80CD2BDB40, param3=1) + 64
>init_iova_domain() + 180
>iommu_setup_dma_ops() + 260
>arch_setup_dma_ops() + 132
>of_dma_configure_id() + 468
>platform_dma_configure() + 32
>really_probe() + 1168
>driver_probe_device() + 268
>__device_attach_driver() + 524
>__device_attach() + 524
>bus_probe_device() + 64
>deferred_probe_work_func() + 260
>process_one_work() + 580
>worker_thread() + 1076
>kthread() + 332
>ret_from_fork() + 16
>
>Signed-off-by: Ning Li <ning.li@xxxxxxxxxxxx>
>Signed-off-by: Yunfei Wang <yf.wang@xxxxxxxxxxxx>
>---
> drivers/iommu/dma-iommu.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>index 09f6e1c0f9c0..b38c5041eeab 100644
>--- a/drivers/iommu/dma-iommu.c
>+++ b/drivers/iommu/dma-iommu.c
>@@ -63,6 +63,7 @@ struct iommu_dma_cookie {
> 
> 	/* Domain for flush queue callback; NULL if flush queue not in use */
> 	struct iommu_domain		*fq_domain;
>+	struct mutex			mutex;
> };
> 
> static DEFINE_STATIC_KEY_FALSE(iommu_deferred_attach_enabled);
>@@ -309,6 +310,7 @@ int iommu_get_dma_cookie(struct iommu_domain *domain)
> 	if (!domain->iova_cookie)
> 		return -ENOMEM;
> 
>+	mutex_init(&domain->iova_cookie->mutex);
> 	return 0;
> }
> 
>@@ -549,26 +551,33 @@ static int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
> 	}
> 
> 	/* start_pfn is always nonzero for an already-initialised domain */
>+	mutex_lock(&cookie->mutex);
>
> 	if (iovad->start_pfn) {
> 		if (1UL << order != iovad->granule ||
> 		    base_pfn != iovad->start_pfn) {
> 			pr_warn("Incompatible range for DMA domain\n");
>-			return -EFAULT;
>+			ret = -EFAULT;
>+			goto done_unlock;
> 		}
> 
>-		return 0;
>+		ret = 0;
>+		goto done_unlock;
> 	}
> 
> 	init_iova_domain(iovad, 1UL << order, base_pfn);
> 	ret = iova_domain_init_rcaches(iovad);
> 	if (ret)
>-		return ret;
>+		goto done_unlock;
> 
> 	/* If the FQ fails we can simply fall back to strict mode */
> 	if (domain->type == IOMMU_DOMAIN_DMA_FQ && iommu_dma_init_fq(domain))
> 		domain->type = IOMMU_DOMAIN_DMA;
> 
>-	return iova_reserve_iommu_regions(dev, domain);
>+	ret = iova_reserve_iommu_regions(dev, domain);
>+
>+done_unlock:
>+	mutex_unlock(&cookie->mutex);
>+	return ret;
> }
> 
> /**
>-- 
>2.18.0
>
>
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