iommu/qcom: Fix bogus detach logic

Currently, the implementation of qcom_iommu_domain_free() is guaranteed
to do one of two things: WARN() and leak everything, or dereference NULL
and crash. That alone is terrible, but in fact the whole idea of trying
to track the liveness of a domain via the qcom_domain->iommu pointer as
a sanity check is full of fundamentally flawed assumptions. Make things
robust and actually functional by not trying to be quite so clever.
Reported-by: Brian Masney <masneyb@onstation.org>
Tested-by: Brian Masney <masneyb@onstation.org>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Fixes: 0ae349a0 ("iommu/qcom: Add qcom_iommu")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/qcom_iommu.c

@@ -344,21 +344,19 @@ static void qcom_iommu_domain_free(struct iommu_domain *domain)
 {
 	struct qcom_iommu_domain *qcom_domain = to_qcom_iommu_domain(domain);
 
-	if (WARN_ON(qcom_domain->iommu))    /* forgot to detach? */
-		return;
-
 	iommu_put_dma_cookie(domain);
 
-	/* NOTE: unmap can be called after client device is powered off,
-	 * for example, with GPUs or anything involving dma-buf.  So we
-	 * cannot rely on the device_link.  Make sure the IOMMU is on to
-	 * avoid unclocked accesses in the TLB inv path:
+	if (qcom_domain->iommu) {
+		/*
+		 * NOTE: unmap can be called after client device is powered
+		 * off, for example, with GPUs or anything involving dma-buf.
+		 * So we cannot rely on the device_link.  Make sure the IOMMU
+		 * is on to avoid unclocked accesses in the TLB inv path:
 		 */
 		pm_runtime_get_sync(qcom_domain->iommu->dev);
-
 		free_io_pgtable_ops(qcom_domain->pgtbl_ops);
-
 		pm_runtime_put_sync(qcom_domain->iommu->dev);
+	}
 
 	kfree(qcom_domain);
 }
@@ -404,7 +402,7 @@ static void qcom_iommu_detach_dev(struct iommu_domain *domain, struct device *de
 	struct qcom_iommu_domain *qcom_domain = to_qcom_iommu_domain(domain);
 	unsigned i;
 
-	if (!qcom_domain->iommu)
+	if (WARN_ON(!qcom_domain->iommu))
 		return;
 
 	pm_runtime_get_sync(qcom_iommu->dev);
@@ -417,8 +415,6 @@ static void qcom_iommu_detach_dev(struct iommu_domain *domain, struct device *de
 		ctx->domain = NULL;
 	}
 	pm_runtime_put_sync(qcom_iommu->dev);
-
-	qcom_domain->iommu = NULL;
 }
 
 static int qcom_iommu_map(struct iommu_domain *domain, unsigned long iova,