[PATCH V4 3/8] xen/grant-dma-ops: Add option to restrict memory access under Xen

Oleksandr Tyshchenko
2022-06-02T19:24:32Z

From: Juergen Gross <jgross@suse.com>

Introduce Xen grant DMA-mapping layer which contains special DMA-mapping
routines for providing grant references as DMA addresses to be used by
frontends (e.g. virtio) in Xen guests.

Add the needed functionality by providing a special set of DMA ops
handling the needed grant operations for the I/O pages.

The subsequent commit will introduce the use case for xen-grant DMA ops
layer to enable using virtio devices in Xen guests in a safe manner.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
Changes RFC -> V1:
- squash with almost all changes from commit (except handling "xen,dev-domid"
property):
"[PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer"
- update commit subject/description and comments in code
- leave only single Kconfig option XEN_VIRTIO and remove architectural
dependencies
- introduce common xen_has_restricted_virtio_memory_access() in xen.h
and update arch_has_restricted_virtio_memory_access() for both
Arm and x86 to call new helper
- use (1ULL << 63) instead of 0x8000000000000000ULL for XEN_GRANT_ADDR_OFF
- implement xen_virtio_dma_map(unmap)_sg() using example in swiotlb-xen.c
- optimize padding by moving "broken" field in struct xen_virtio_data
- remove unneeded per-device spinlock
- remove the inclusion of virtio_config.h
- remane everything according to the new naming scheme:
s/virtio/grant_dma
- add new hidden config option XEN_GRANT_DMA_OPS

Changes V1 -> V2:
- fix checkpatch.pl warnings
- remove the inclusion of linux/pci.h
- rework to use xarray for data context
- remove EXPORT_SYMBOL_GPL(xen_grant_setup_dma_ops);
- remove the line of * after SPDX-License-Identifier
- split changes into grant-dma-ops.c and arch_has_restricted_virtio_memory_access()
and update commit subject/description accordingly
- remove "default n" for config XEN_VIRTIO
- implement xen_grant_dma_alloc(free)_pages()

Changes V2 -> V3:
- Stefano already gave his Reviewed-by, I dropped it due to the changes (minor)
- remane field "dev_domid" in struct xen_grant_dma_data to "backend_domid"
- remove local variable "domid" in xen_grant_setup_dma_ops()

Changes V3 -> V4:
- add Stefano's R-b
---
---
drivers/xen/Kconfig | 4 +
drivers/xen/Makefile | 1 +
drivers/xen/grant-dma-ops.c | 311 ++++++++++++++++++++++++++++++++++++++++++++
include/xen/xen-ops.h | 8 ++
4 files changed, 324 insertions(+)
create mode 100644 drivers/xen/grant-dma-ops.c

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 120d32f..313a9127 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -335,4 +335,8 @@ config XEN_UNPOPULATED_ALLOC
having to balloon out RAM regions in order to obtain physical memory
space to create such mappings.

+config XEN_GRANT_DMA_OPS
+ bool
+ select DMA_OPS
+
endmenu
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 5aae66e..1a23cb0 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -39,3 +39,4 @@ xen-gntalloc-y := gntalloc.o
xen-privcmd-y := privcmd.o privcmd-buf.o
obj-$(CONFIG_XEN_FRONT_PGDIR_SHBUF) += xen-front-pgdir-shbuf.o
obj-$(CONFIG_XEN_UNPOPULATED_ALLOC) += unpopulated-alloc.o
+obj-$(CONFIG_XEN_GRANT_DMA_OPS) += grant-dma-ops.o
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
new file mode 100644
index 00000000..44659f4
--- /dev/null
+++ b/drivers/xen/grant-dma-ops.c
@@ -0,0 +1,311 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Xen grant DMA-mapping layer - contains special DMA-mapping routines
+ * for providing grant references as DMA addresses to be used by frontends
+ * (e.g. virtio) in Xen guests
+ *
+ * Copyright (c) 2021, Juergen Gross <jgross@suse.com>
+ */
+
+#include <linux/module.h>
+#include <linux/dma-map-ops.h>
+#include <linux/of.h>
+#include <linux/pfn.h>
+#include <linux/xarray.h>
+#include <xen/xen.h>
+#include <xen/grant_table.h>
+
+struct xen_grant_dma_data {
+ /* The ID of backend domain */
+ domid_t backend_domid;
+ /* Is device behaving sane? */
+ bool broken;
+};
+
+static DEFINE_XARRAY(xen_grant_dma_devices);
+
+#define XEN_GRANT_DMA_ADDR_OFF (1ULL << 63)
+
+static inline dma_addr_t grant_to_dma(grant_ref_t grant)
+{
+ return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant << PAGE_SHIFT);
+}
+
+static inline grant_ref_t dma_to_grant(dma_addr_t dma)
+{
+ return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >> PAGE_SHIFT);
+}
+
+static struct xen_grant_dma_data *find_xen_grant_dma_data(struct device *dev)
+{
+ struct xen_grant_dma_data *data;
+
+ xa_lock(&xen_grant_dma_devices);
+ data = xa_load(&xen_grant_dma_devices, (unsigned long)dev);
+ xa_unlock(&xen_grant_dma_devices);
+
+ return data;
+}
+
+/*
+ * DMA ops for Xen frontends (e.g. virtio).
+ *
+ * Used to act as a kind of software IOMMU for Xen guests by using grants as
+ * DMA addresses.
+ * Such a DMA address is formed by using the grant reference as a frame
+ * number and setting the highest address bit (this bit is for the backend
+ * to be able to distinguish it from e.g. a mmio address).
+ *
+ * Note that for now we hard wire dom0 to be the backend domain. In order
+ * to support any domain as backend we'd need to add a way to communicate
+ * the domid of this backend, e.g. via Xenstore, via the PCI-device's
+ * config space or DT/ACPI.
+ */
+static void *xen_grant_dma_alloc(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t gfp,
+ unsigned long attrs)
+{
+ struct xen_grant_dma_data *data;
+ unsigned int i, n_pages = PFN_UP(size);
+ unsigned long pfn;
+ grant_ref_t grant;
+ void *ret;
+
+ data = find_xen_grant_dma_data(dev);
+ if (!data)
+ return NULL;
+
+ if (unlikely(data->broken))
+ return NULL;
+
+ ret = alloc_pages_exact(n_pages * PAGE_SIZE, gfp);
+ if (!ret)
+ return NULL;
+
+ pfn = virt_to_pfn(ret);
+
+ if (gnttab_alloc_grant_reference_seq(n_pages, &grant)) {
+ free_pages_exact(ret, n_pages * PAGE_SIZE);
+ return NULL;
+ }
+
+ for (i = 0; i < n_pages; i++) {
+ gnttab_grant_foreign_access_ref(grant + i, data->backend_domid,
+ pfn_to_gfn(pfn + i), 0);
+ }
+
+ *dma_handle = grant_to_dma(grant);
+
+ return ret;
+}
+
+static void xen_grant_dma_free(struct device *dev, size_t size, void *vaddr,
+ dma_addr_t dma_handle, unsigned long attrs)
+{
+ struct xen_grant_dma_data *data;
+ unsigned int i, n_pages = PFN_UP(size);
+ grant_ref_t grant;
+
+ data = find_xen_grant_dma_data(dev);
+ if (!data)
+ return;
+
+ if (unlikely(data->broken))
+ return;
+
+ grant = dma_to_grant(dma_handle);
+
+ for (i = 0; i < n_pages; i++) {
+ if (unlikely(!gnttab_end_foreign_access_ref(grant + i))) {
+ dev_alert(dev, "Grant still in use by backend domain, disabled for further use\n");
+ data->broken = true;
+ return;
+ }
+ }
+
+ gnttab_free_grant_reference_seq(grant, n_pages);
+
+ free_pages_exact(vaddr, n_pages * PAGE_SIZE);
+}
+
+static struct page *xen_grant_dma_alloc_pages(struct device *dev, size_t size,
+ dma_addr_t *dma_handle,
+ enum dma_data_direction dir,
+ gfp_t gfp)
+{
+ void *vaddr;
+
+ vaddr = xen_grant_dma_alloc(dev, size, dma_handle, gfp, 0);
+ if (!vaddr)
+ return NULL;
+
+ return virt_to_page(vaddr);
+}
+
+static void xen_grant_dma_free_pages(struct device *dev, size_t size,
+ struct page *vaddr, dma_addr_t dma_handle,
+ enum dma_data_direction dir)
+{
+ xen_grant_dma_free(dev, size, page_to_virt(vaddr), dma_handle, 0);
+}
+
+static dma_addr_t xen_grant_dma_map_page(struct device *dev, struct page *page,
+ unsigned long offset, size_t size,
+ enum dma_data_direction dir,
+ unsigned long attrs)
+{
+ struct xen_grant_dma_data *data;
+ unsigned int i, n_pages = PFN_UP(size);
+ grant_ref_t grant;
+ dma_addr_t dma_handle;
+
+ if (WARN_ON(dir == DMA_NONE))
+ return DMA_MAPPING_ERROR;
+
+ data = find_xen_grant_dma_data(dev);
+ if (!data)
+ return DMA_MAPPING_ERROR;
+
+ if (unlikely(data->broken))
+ return DMA_MAPPING_ERROR;
+
+ if (gnttab_alloc_grant_reference_seq(n_pages, &grant))
+ return DMA_MAPPING_ERROR;
+
+ for (i = 0; i < n_pages; i++) {
+ gnttab_grant_foreign_access_ref(grant + i, data->backend_domid,
+ xen_page_to_gfn(page) + i, dir == DMA_TO_DEVICE);
+ }
+
+ dma_handle = grant_to_dma(grant) + offset;
+
+ return dma_handle;
+}
+
+static void xen_grant_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
+ size_t size, enum dma_data_direction dir,
+ unsigned long attrs)
+{
+ struct xen_grant_dma_data *data;
+ unsigned int i, n_pages = PFN_UP(size);
+ grant_ref_t grant;
+
+ if (WARN_ON(dir == DMA_NONE))
+ return;
+
+ data = find_xen_grant_dma_data(dev);
+ if (!data)
+ return;
+
+ if (unlikely(data->broken))
+ return;
+
+ grant = dma_to_grant(dma_handle);
+
+ for (i = 0; i < n_pages; i++) {
+ if (unlikely(!gnttab_end_foreign_access_ref(grant + i))) {
+ dev_alert(dev, "Grant still in use by backend domain, disabled for further use\n");
+ data->broken = true;
+ return;
+ }
+ }
+
+ gnttab_free_grant_reference_seq(grant, n_pages);
+}
+
+static void xen_grant_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
+ int nents, enum dma_data_direction dir,
+ unsigned long attrs)
+{
+ struct scatterlist *s;
+ unsigned int i;
+
+ if (WARN_ON(dir == DMA_NONE))
+ return;
+
+ for_each_sg(sg, s, nents, i)
+ xen_grant_dma_unmap_page(dev, s->dma_address, sg_dma_len(s), dir,
+ attrs);
+}
+
+static int xen_grant_dma_map_sg(struct device *dev, struct scatterlist *sg,
+ int nents, enum dma_data_direction dir,
+ unsigned long attrs)
+{
+ struct scatterlist *s;
+ unsigned int i;
+
+ if (WARN_ON(dir == DMA_NONE))
+ return -EINVAL;
+
+ for_each_sg(sg, s, nents, i) {
+ s->dma_address = xen_grant_dma_map_page(dev, sg_page(s), s->offset,
+ s->length, dir, attrs);
+ if (s->dma_address == DMA_MAPPING_ERROR)
+ goto out;
+
+ sg_dma_len(s) = s->length;
+ }
+
+ return nents;
+
+out:
+ xen_grant_dma_unmap_sg(dev, sg, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
+ sg_dma_len(sg) = 0;
+
+ return -EIO;
+}
+
+static int xen_grant_dma_supported(struct device *dev, u64 mask)
+{
+ return mask == DMA_BIT_MASK(64);
+}
+
+static const struct dma_map_ops xen_grant_dma_ops = {
+ .alloc = xen_grant_dma_alloc,
+ .free = xen_grant_dma_free,
+ .alloc_pages = xen_grant_dma_alloc_pages,
+ .free_pages = xen_grant_dma_free_pages,
+ .mmap = dma_common_mmap,
+ .get_sgtable = dma_common_get_sgtable,
+ .map_page = xen_grant_dma_map_page,
+ .unmap_page = xen_grant_dma_unmap_page,
+ .map_sg = xen_grant_dma_map_sg,
+ .unmap_sg = xen_grant_dma_unmap_sg,
+ .dma_supported = xen_grant_dma_supported,
+};
+
+void xen_grant_setup_dma_ops(struct device *dev)
+{
+ struct xen_grant_dma_data *data;
+
+ data = find_xen_grant_dma_data(dev);
+ if (data) {
+ dev_err(dev, "Xen grant DMA data is already created\n");
+ return;
+ }
+
+ data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+ if (!data)
+ goto err;
+
+ /* XXX The dom0 is hardcoded as the backend domain for now */
+ data->backend_domid = 0;
+
+ if (xa_err(xa_store(&xen_grant_dma_devices, (unsigned long)dev, data,
+ GFP_KERNEL))) {
+ dev_err(dev, "Cannot store Xen grant DMA data\n");
+ goto err;
+ }
+
+ dev->dma_ops = &xen_grant_dma_ops;
+
+ return;
+
+err:
+ dev_err(dev, "Cannot set up Xen grant DMA ops, retain platform DMA ops\n");
+}
+
+MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
+MODULE_AUTHOR("Juergen Gross <jgross@suse.com>");
+MODULE_LICENSE("GPL");
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index a3584a3..4f9fad5 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -221,4 +221,12 @@ static inline void xen_preemptible_hcall_end(void) { }

#endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */

+#ifdef CONFIG_XEN_GRANT_DMA_OPS
+void xen_grant_setup_dma_ops(struct device *dev);
+#else
+static inline void xen_grant_setup_dma_ops(struct device *dev)
+{
+}
+#endif /* CONFIG_XEN_GRANT_DMA_OPS */
+
#endif /* INCLUDE_XEN_OPS_H */
--
2.7.4