xen: Introduce shared buffer helpers for page directory... (b3383974) · Commits · 戴 / test

drivers/xen/Kconfig

+3 −0

Original line number	Diff line number	Diff line
		@@ -340,4 +340,7 @@ config XEN_SYMS
		config XEN_HAVE_VPMU
		bool

		config XEN_FRONT_PGDIR_SHBUF
		tristate

		endmenu

drivers/xen/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -44,3 +44,4 @@ xen-gntdev-y := gntdev.o
		xen-gntdev-$(CONFIG_XEN_GNTDEV_DMABUF) += gntdev-dmabuf.o
		xen-gntalloc-y := gntalloc.o
		xen-privcmd-y := privcmd.o privcmd-buf.o
		obj-$(CONFIG_XEN_FRONT_PGDIR_SHBUF) += xen-front-pgdir-shbuf.o

drivers/xen/xen-front-pgdir-shbuf.c

0 → 100644

+553 −0

Original line number	Diff line number	Diff line
		// SPDX-License-Identifier: GPL-2.0 OR MIT

		/*
		* Xen frontend/backend page directory based shared buffer
		* helper module.
		*
		* Copyright (C) 2018 EPAM Systems Inc.
		*
		* Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
		*/

		#include <linux/module.h>
		#include <linux/errno.h>
		#include <linux/mm.h>

		#include <asm/xen/hypervisor.h>
		#include <xen/balloon.h>
		#include <xen/xen.h>
		#include <xen/xenbus.h>
		#include <xen/interface/io/ring.h>

		#include <xen/xen-front-pgdir-shbuf.h>

		#ifndef GRANT_INVALID_REF
		/*
		* FIXME: usage of grant reference 0 as invalid grant reference:
		* grant reference 0 is valid, but never exposed to a PV driver,
		* because of the fact it is already in use/reserved by the PV console.
		*/
		#define GRANT_INVALID_REF 0
		#endif

		/**
		* This structure represents the structure of a shared page
		* that contains grant references to the pages of the shared
		* buffer. This structure is common to many Xen para-virtualized
		* protocols at include/xen/interface/io/
		*/
		struct xen_page_directory {
		grant_ref_t gref_dir_next_page;
		grant_ref_t gref[1]; /* Variable length */
		};

		/**
		* Shared buffer ops which are differently implemented
		* depending on the allocation mode, e.g. if the buffer
		* is allocated by the corresponding backend or frontend.
		* Some of the operations.
		*/
		struct xen_front_pgdir_shbuf_ops {
		/*
		* Calculate number of grefs required to handle this buffer,
		* e.g. if grefs are required for page directory only or the buffer
		* pages as well.
		*/
		void (calc_num_grefs)(struct xen_front_pgdir_shbuf buf);

		/* Fill page directory according to para-virtual display protocol. */
		void (fill_page_dir)(struct xen_front_pgdir_shbuf buf);

		/* Claim grant references for the pages of the buffer. */
		int (grant_refs_for_buffer)(struct xen_front_pgdir_shbuf buf,
		grant_ref_t *priv_gref_head, int gref_idx);

		/* Map grant references of the buffer. */
		int (map)(struct xen_front_pgdir_shbuf buf);

		/* Unmap grant references of the buffer. */
		int (unmap)(struct xen_front_pgdir_shbuf buf);
		};

		/**
		* Get granted reference to the very first page of the
		* page directory. Usually this is passed to the backend,
		* so it can find/fill the grant references to the buffer's
		* pages.
		*
		* \param buf shared buffer which page directory is of interest.
		* \return granted reference to the very first page of the
		* page directory.
		*/
		grant_ref_t
		xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf)
		{
		if (!buf->grefs)
		return GRANT_INVALID_REF;

		return buf->grefs[0];
		}
		EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_get_dir_start);

		/**
		* Map granted references of the shared buffer.
		*
		* Depending on the shared buffer mode of allocation
		* (be_alloc flag) this can either do nothing (for buffers
		* shared by the frontend itself) or map the provided granted
		* references onto the backing storage (buf->pages).
		*
		* \param buf shared buffer which grants to be maped.
		* \return zero on success or a negative number on failure.
		*/
		int xen_front_pgdir_shbuf_map(struct xen_front_pgdir_shbuf *buf)
		{
		if (buf->ops && buf->ops->map)
		return buf->ops->map(buf);

		/* No need to map own grant references. */
		return 0;
		}
		EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_map);

		/**
		* Unmap granted references of the shared buffer.
		*
		* Depending on the shared buffer mode of allocation
		* (be_alloc flag) this can either do nothing (for buffers
		* shared by the frontend itself) or unmap the provided granted
		* references.
		*
		* \param buf shared buffer which grants to be unmaped.
		* \return zero on success or a negative number on failure.
		*/
		int xen_front_pgdir_shbuf_unmap(struct xen_front_pgdir_shbuf *buf)
		{
		if (buf->ops && buf->ops->unmap)
		return buf->ops->unmap(buf);

		/* No need to unmap own grant references. */
		return 0;
		}
		EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_unmap);

		/**
		* Free all the resources of the shared buffer.
		*
		* \param buf shared buffer which resources to be freed.
		*/
		void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf)
		{
		if (buf->grefs) {
		int i;

		for (i = 0; i < buf->num_grefs; i++)
		if (buf->grefs[i] != GRANT_INVALID_REF)
		gnttab_end_foreign_access(buf->grefs[i],
		0, 0UL);
		}
		kfree(buf->grefs);
		kfree(buf->directory);
		}
		EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_free);

		/*
		* Number of grefs a page can hold with respect to the
		* struct xen_page_directory header.
		*/
		#define XEN_NUM_GREFS_PER_PAGE ((PAGE_SIZE - \
		offsetof(struct xen_page_directory, \
		gref)) / sizeof(grant_ref_t))

		/**
		* Get the number of pages the page directory consumes itself.
		*
		* \param buf shared buffer.
		*/
		static int get_num_pages_dir(struct xen_front_pgdir_shbuf *buf)
		{
		return DIV_ROUND_UP(buf->num_pages, XEN_NUM_GREFS_PER_PAGE);
		}

		/**
		* Calculate the number of grant references needed to share the buffer
		* and its pages when backend allocates the buffer.
		*
		* \param buf shared buffer.
		*/
		static void backend_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
		{
		/* Only for pages the page directory consumes itself. */
		buf->num_grefs = get_num_pages_dir(buf);
		}

		/**
		* Calculate the number of grant references needed to share the buffer
		* and its pages when frontend allocates the buffer.
		*
		* \param buf shared buffer.
		*/
		static void guest_calc_num_grefs(struct xen_front_pgdir_shbuf *buf)
		{
		/*
		* Number of pages the page directory consumes itself
		* plus grefs for the buffer pages.
		*/
		buf->num_grefs = get_num_pages_dir(buf) + buf->num_pages;
		}

		#define xen_page_to_vaddr(page) \
		((uintptr_t)pfn_to_kaddr(page_to_xen_pfn(page)))

		/**
		* Unmap the buffer previously mapped with grant references
		* provided by the backend.
		*
		* \param buf shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		static int backend_unmap(struct xen_front_pgdir_shbuf *buf)
		{
		struct gnttab_unmap_grant_ref *unmap_ops;
		int i, ret;

		if (!buf->pages \|\| !buf->backend_map_handles \|\| !buf->grefs)
		return 0;

		unmap_ops = kcalloc(buf->num_pages, sizeof(*unmap_ops),
		GFP_KERNEL);
		if (!unmap_ops)
		return -ENOMEM;

		for (i = 0; i < buf->num_pages; i++) {
		phys_addr_t addr;

		addr = xen_page_to_vaddr(buf->pages[i]);
		gnttab_set_unmap_op(&unmap_ops[i], addr, GNTMAP_host_map,
		buf->backend_map_handles[i]);
		}

		ret = gnttab_unmap_refs(unmap_ops, NULL, buf->pages,
		buf->num_pages);

		for (i = 0; i < buf->num_pages; i++) {
		if (unlikely(unmap_ops[i].status != GNTST_okay))
		dev_err(&buf->xb_dev->dev,
		"Failed to unmap page %d: %d\n",
		i, unmap_ops[i].status);
		}

		if (ret)
		dev_err(&buf->xb_dev->dev,
		"Failed to unmap grant references, ret %d", ret);

		kfree(unmap_ops);
		kfree(buf->backend_map_handles);
		buf->backend_map_handles = NULL;
		return ret;
		}

		/**
		* Map the buffer with grant references provided by the backend.
		*
		* \param buf shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		static int backend_map(struct xen_front_pgdir_shbuf *buf)
		{
		struct gnttab_map_grant_ref *map_ops = NULL;
		unsigned char *ptr;
		int ret, cur_gref, cur_dir_page, cur_page, grefs_left;

		map_ops = kcalloc(buf->num_pages, sizeof(*map_ops), GFP_KERNEL);
		if (!map_ops)
		return -ENOMEM;

		buf->backend_map_handles = kcalloc(buf->num_pages,
		sizeof(*buf->backend_map_handles),
		GFP_KERNEL);
		if (!buf->backend_map_handles) {
		kfree(map_ops);
		return -ENOMEM;
		}

		/*
		* Read page directory to get grefs from the backend: for external
		* buffer we only allocate buf->grefs for the page directory,
		* so buf->num_grefs has number of pages in the page directory itself.
		*/
		ptr = buf->directory;
		grefs_left = buf->num_pages;
		cur_page = 0;
		for (cur_dir_page = 0; cur_dir_page < buf->num_grefs; cur_dir_page++) {
		struct xen_page_directory *page_dir =
		(struct xen_page_directory *)ptr;
		int to_copy = XEN_NUM_GREFS_PER_PAGE;

		if (to_copy > grefs_left)
		to_copy = grefs_left;

		for (cur_gref = 0; cur_gref < to_copy; cur_gref++) {
		phys_addr_t addr;

		addr = xen_page_to_vaddr(buf->pages[cur_page]);
		gnttab_set_map_op(&map_ops[cur_page], addr,
		GNTMAP_host_map,
		page_dir->gref[cur_gref],
		buf->xb_dev->otherend_id);
		cur_page++;
		}

		grefs_left -= to_copy;
		ptr += PAGE_SIZE;
		}
		ret = gnttab_map_refs(map_ops, NULL, buf->pages, buf->num_pages);

		/* Save handles even if error, so we can unmap. */
		for (cur_page = 0; cur_page < buf->num_pages; cur_page++) {
		buf->backend_map_handles[cur_page] = map_ops[cur_page].handle;
		if (unlikely(map_ops[cur_page].status != GNTST_okay))
		dev_err(&buf->xb_dev->dev,
		"Failed to map page %d: %d\n",
		cur_page, map_ops[cur_page].status);
		}

		if (ret) {
		dev_err(&buf->xb_dev->dev,
		"Failed to map grant references, ret %d", ret);
		backend_unmap(buf);
		}

		kfree(map_ops);
		return ret;
		}

		/**
		* Fill page directory with grant references to the pages of the
		* page directory itself.
		*
		* The grant references to the buffer pages are provided by the
		* backend in this case.
		*
		* \param buf shared buffer.
		*/
		static void backend_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
		{
		struct xen_page_directory *page_dir;
		unsigned char *ptr;
		int i, num_pages_dir;

		ptr = buf->directory;
		num_pages_dir = get_num_pages_dir(buf);

		/* Fill only grefs for the page directory itself. */
		for (i = 0; i < num_pages_dir - 1; i++) {
		page_dir = (struct xen_page_directory *)ptr;

		page_dir->gref_dir_next_page = buf->grefs[i + 1];
		ptr += PAGE_SIZE;
		}
		/* Last page must say there is no more pages. */
		page_dir = (struct xen_page_directory *)ptr;
		page_dir->gref_dir_next_page = GRANT_INVALID_REF;
		}

		/**
		* Fill page directory with grant references to the pages of the
		* page directory and the buffer we share with the backend.
		*
		* \param buf shared buffer.
		*/
		static void guest_fill_page_dir(struct xen_front_pgdir_shbuf *buf)
		{
		unsigned char *ptr;
		int cur_gref, grefs_left, to_copy, i, num_pages_dir;

		ptr = buf->directory;
		num_pages_dir = get_num_pages_dir(buf);

		/*
		* While copying, skip grefs at start, they are for pages
		* granted for the page directory itself.
		*/
		cur_gref = num_pages_dir;
		grefs_left = buf->num_pages;
		for (i = 0; i < num_pages_dir; i++) {
		struct xen_page_directory *page_dir =
		(struct xen_page_directory *)ptr;

		if (grefs_left <= XEN_NUM_GREFS_PER_PAGE) {
		to_copy = grefs_left;
		page_dir->gref_dir_next_page = GRANT_INVALID_REF;
		} else {
		to_copy = XEN_NUM_GREFS_PER_PAGE;
		page_dir->gref_dir_next_page = buf->grefs[i + 1];
		}
		memcpy(&page_dir->gref, &buf->grefs[cur_gref],
		to_copy * sizeof(grant_ref_t));
		ptr += PAGE_SIZE;
		grefs_left -= to_copy;
		cur_gref += to_copy;
		}
		}

		/**
		* Grant references to the frontend's buffer pages.
		*
		* These will be shared with the backend, so it can
		* access the buffer's data.
		*
		* \param buf shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		static int guest_grant_refs_for_buffer(struct xen_front_pgdir_shbuf *buf,
		grant_ref_t *priv_gref_head,
		int gref_idx)
		{
		int i, cur_ref, otherend_id;

		otherend_id = buf->xb_dev->otherend_id;
		for (i = 0; i < buf->num_pages; i++) {
		cur_ref = gnttab_claim_grant_reference(priv_gref_head);
		if (cur_ref < 0)
		return cur_ref;

		gnttab_grant_foreign_access_ref(cur_ref, otherend_id,
		xen_page_to_gfn(buf->pages[i]),
		0);
		buf->grefs[gref_idx++] = cur_ref;
		}
		return 0;
		}

		/**
		* Grant all the references needed to share the buffer.
		*
		* Grant references to the page directory pages and, if
		* needed, also to the pages of the shared buffer data.
		*
		* \param buf shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		static int grant_references(struct xen_front_pgdir_shbuf *buf)
		{
		grant_ref_t priv_gref_head;
		int ret, i, j, cur_ref;
		int otherend_id, num_pages_dir;

		ret = gnttab_alloc_grant_references(buf->num_grefs, &priv_gref_head);
		if (ret < 0) {
		dev_err(&buf->xb_dev->dev,
		"Cannot allocate grant references\n");
		return ret;
		}

		otherend_id = buf->xb_dev->otherend_id;
		j = 0;
		num_pages_dir = get_num_pages_dir(buf);
		for (i = 0; i < num_pages_dir; i++) {
		unsigned long frame;

		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
		if (cur_ref < 0)
		return cur_ref;

		frame = xen_page_to_gfn(virt_to_page(buf->directory +
		PAGE_SIZE * i));
		gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
		buf->grefs[j++] = cur_ref;
		}

		if (buf->ops->grant_refs_for_buffer) {
		ret = buf->ops->grant_refs_for_buffer(buf, &priv_gref_head, j);
		if (ret)
		return ret;
		}

		gnttab_free_grant_references(priv_gref_head);
		return 0;
		}

		/**
		* Allocate all required structures to mange shared buffer.
		*
		* \param buf shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		static int alloc_storage(struct xen_front_pgdir_shbuf *buf)
		{
		buf->grefs = kcalloc(buf->num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
		if (!buf->grefs)
		return -ENOMEM;

		buf->directory = kcalloc(get_num_pages_dir(buf), PAGE_SIZE, GFP_KERNEL);
		if (!buf->directory)
		return -ENOMEM;

		return 0;
		}

		/*
		* For backend allocated buffers we don't need grant_refs_for_buffer
		* as those grant references are allocated at backend side.
		*/
		static const struct xen_front_pgdir_shbuf_ops backend_ops = {
		.calc_num_grefs = backend_calc_num_grefs,
		.fill_page_dir = backend_fill_page_dir,
		.map = backend_map,
		.unmap = backend_unmap
		};

		/*
		* For locally granted references we do not need to map/unmap
		* the references.
		*/
		static const struct xen_front_pgdir_shbuf_ops local_ops = {
		.calc_num_grefs = guest_calc_num_grefs,
		.fill_page_dir = guest_fill_page_dir,
		.grant_refs_for_buffer = guest_grant_refs_for_buffer,
		};

		/**
		* Allocate a new instance of a shared buffer.
		*
		* \param cfg configuration to be used while allocating a new shared buffer.
		* \return zero on success or a negative number on failure.
		*/
		int xen_front_pgdir_shbuf_alloc(struct xen_front_pgdir_shbuf_cfg *cfg)
		{
		struct xen_front_pgdir_shbuf *buf = cfg->pgdir;
		int ret;

		if (cfg->be_alloc)
		buf->ops = &backend_ops;
		else
		buf->ops = &local_ops;
		buf->xb_dev = cfg->xb_dev;
		buf->num_pages = cfg->num_pages;
		buf->pages = cfg->pages;

		buf->ops->calc_num_grefs(buf);

		ret = alloc_storage(buf);
		if (ret)
		goto fail;

		ret = grant_references(buf);
		if (ret)
		goto fail;

		buf->ops->fill_page_dir(buf);

		return 0;

		fail:
		xen_front_pgdir_shbuf_free(buf);
		return ret;
		}
		EXPORT_SYMBOL_GPL(xen_front_pgdir_shbuf_alloc);

		MODULE_DESCRIPTION("Xen frontend/backend page directory based "
		"shared buffer handling");
		MODULE_AUTHOR("Oleksandr Andrushchenko");
		MODULE_LICENSE("GPL");

include/xen/xen-front-pgdir-shbuf.h

0 → 100644

+89 −0

Original line number	Diff line number	Diff line
		/* SPDX-License-Identifier: GPL-2.0 OR MIT */

		/*
		* Xen frontend/backend page directory based shared buffer
		* helper module.
		*
		* Copyright (C) 2018 EPAM Systems Inc.
		*
		* Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
		*/

		#ifndef __XEN_FRONT_PGDIR_SHBUF_H_
		#define __XEN_FRONT_PGDIR_SHBUF_H_

		#include <linux/kernel.h>

		#include <xen/grant_table.h>

		struct xen_front_pgdir_shbuf_ops;

		struct xen_front_pgdir_shbuf {
		/*
		* Number of references granted for the backend use:
		*
		* - for frontend allocated/imported buffers this holds the number
		* of grant references for the page directory and the pages
		* of the buffer
		*
		* - for the buffer provided by the backend this only holds the number
		* of grant references for the page directory itself as grant
		* references for the buffer will be provided by the backend.
		*/
		int num_grefs;
		grant_ref_t *grefs;
		/* Page directory backing storage. */
		u8 *directory;

		/*
		* Number of pages for the shared buffer itself (excluding the page
		* directory).
		*/
		int num_pages;
		/*
		* Backing storage of the shared buffer: these are the pages being
		* shared.
		*/
		struct page **pages;

		struct xenbus_device *xb_dev;

		/* These are the ops used internally depending on be_alloc mode. */
		const struct xen_front_pgdir_shbuf_ops *ops;

		/* Xen map handles for the buffer allocated by the backend. */
		grant_handle_t *backend_map_handles;
		};

		struct xen_front_pgdir_shbuf_cfg {
		struct xenbus_device *xb_dev;

		/* Number of pages of the buffer backing storage. */
		int num_pages;
		/* Pages of the buffer to be shared. */
		struct page **pages;

		/*
		* This is allocated outside because there are use-cases when
		* the buffer structure is allocated as a part of a bigger one.
		*/
		struct xen_front_pgdir_shbuf *pgdir;
		/*
		* Mode of grant reference sharing: if set then backend will share
		* grant references to the buffer with the frontend.
		*/
		int be_alloc;
		};

		int xen_front_pgdir_shbuf_alloc(struct xen_front_pgdir_shbuf_cfg *cfg);

		grant_ref_t
		xen_front_pgdir_shbuf_get_dir_start(struct xen_front_pgdir_shbuf *buf);

		int xen_front_pgdir_shbuf_map(struct xen_front_pgdir_shbuf *buf);

		int xen_front_pgdir_shbuf_unmap(struct xen_front_pgdir_shbuf *buf);

		void xen_front_pgdir_shbuf_free(struct xen_front_pgdir_shbuf *buf);

		#endif /* __XEN_FRONT_PGDIR_SHBUF_H_ */

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