On Tue, 31 May 2022, Oleksandr Tyshchenko wrote:
> From: Juergen Gross <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Oleksandr Tyshchenko <[email protected]>
Reviewed-by: Stefano Stabellini <[email protected]>
> ---
> 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()
> ---
> 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 <[email protected]>
> + */
> +
> +#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 <[email protected]>");
> +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
>
>
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