iommu/sva: Add PASID helpers

Let IOMMU drivers allocate a single PASID per mm. Store the mm in the
IOASID set to allow refcounting and searching mm by PASID, when handling
an I/O page fault.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20201106155048.997886-3-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/Kconfig

@@ -103,6 +103,11 @@ config IOMMU_DMA
 	select IRQ_MSI_IOMMU
 	select NEED_SG_DMA_LENGTH
 
+# Shared Virtual Addressing library
+config IOMMU_SVA_LIB
+	bool
+	select IOASID
+
 config FSL_PAMU
 	bool "Freescale IOMMU support"
 	depends on PCI

drivers/iommu/Makefile

@@ -27,3 +27,4 @@ obj-$(CONFIG_FSL_PAMU) += fsl_pamu.o fsl_pamu_domain.o
 obj-$(CONFIG_S390_IOMMU) += s390-iommu.o
 obj-$(CONFIG_HYPERV_IOMMU) += hyperv-iommu.o
 obj-$(CONFIG_VIRTIO_IOMMU) += virtio-iommu.o
+obj-$(CONFIG_IOMMU_SVA_LIB) += iommu-sva-lib.o

drivers/iommu/iommu-sva-lib.c

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Helpers for IOMMU drivers implementing SVA
+ */
+#include <linux/mutex.h>
+#include <linux/sched/mm.h>
+
+#include "iommu-sva-lib.h"
+
+static DEFINE_MUTEX(iommu_sva_lock);
+static DECLARE_IOASID_SET(iommu_sva_pasid);
+
+/**
+ * iommu_sva_alloc_pasid - Allocate a PASID for the mm
+ * @mm: the mm
+ * @min: minimum PASID value (inclusive)
+ * @max: maximum PASID value (inclusive)
+ *
+ * Try to allocate a PASID for this mm, or take a reference to the existing one
+ * provided it fits within the [@min, @max] range. On success the PASID is
+ * available in mm->pasid, and must be released with iommu_sva_free_pasid().
+ * @min must be greater than 0, because 0 indicates an unused mm->pasid.
+ *
+ * Returns 0 on success and < 0 on error.
+ */
+int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
+{
+	int ret = 0;
+	ioasid_t pasid;
+
+	if (min == INVALID_IOASID || max == INVALID_IOASID ||
+	    min == 0 || max < min)
+		return -EINVAL;
+
+	mutex_lock(&iommu_sva_lock);
+	if (mm->pasid) {
+		if (mm->pasid >= min && mm->pasid <= max)
+			ioasid_get(mm->pasid);
+		else
+			ret = -EOVERFLOW;
+	} else {
+		pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
+		if (pasid == INVALID_IOASID)
+			ret = -ENOMEM;
+		else
+			mm->pasid = pasid;
+	}
+	mutex_unlock(&iommu_sva_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
+
+/**
+ * iommu_sva_free_pasid - Release the mm's PASID
+ * @mm: the mm
+ *
+ * Drop one reference to a PASID allocated with iommu_sva_alloc_pasid()
+ */
+void iommu_sva_free_pasid(struct mm_struct *mm)
+{
+	mutex_lock(&iommu_sva_lock);
+	if (ioasid_put(mm->pasid))
+		mm->pasid = 0;
+	mutex_unlock(&iommu_sva_lock);
+}
+EXPORT_SYMBOL_GPL(iommu_sva_free_pasid);
+
+/* ioasid_find getter() requires a void * argument */
+static bool __mmget_not_zero(void *mm)
+{
+	return mmget_not_zero(mm);
+}
+
+/**
+ * iommu_sva_find() - Find mm associated to the given PASID
+ * @pasid: Process Address Space ID assigned to the mm
+ *
+ * On success a reference to the mm is taken, and must be released with mmput().
+ *
+ * Returns the mm corresponding to this PASID, or an error if not found.
+ */
+struct mm_struct *iommu_sva_find(ioasid_t pasid)
+{
+	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
+}
+EXPORT_SYMBOL_GPL(iommu_sva_find);

drivers/iommu/iommu-sva-lib.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * SVA library for IOMMU drivers
+ */
+#ifndef _IOMMU_SVA_LIB_H
+#define _IOMMU_SVA_LIB_H
+
+#include <linux/ioasid.h>
+#include <linux/mm_types.h>
+
+int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max);
+void iommu_sva_free_pasid(struct mm_struct *mm);
+struct mm_struct *iommu_sva_find(ioasid_t pasid);
+
+#endif /* _IOMMU_SVA_LIB_H */