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Subject[PATCH v2 5/8] drm/xen-front: Implement handling of shared display buffers
Date
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Implement shared buffer handling according to the
para-virtualized display device protocol at xen/interface/io/displif.h:
- handle page directories according to displif protocol:
- allocate and share page directories
- grant references to the required set of pages for the
page directory
- allocate xen balllooned pages via Xen balloon driver
with alloc_xenballooned_pages/free_xenballooned_pages
- grant references to the required set of pages for the
shared buffer itself
- implement pages map/unmap for the buffers allocated by the
backend (gnttab_map_refs/gnttab_unmap_refs)

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
drivers/gpu/drm/xen/Makefile | 1 +
drivers/gpu/drm/xen/xen_drm_front.c | 8 +
drivers/gpu/drm/xen/xen_drm_front_shbuf.c | 432 ++++++++++++++++++++++++++++++
drivers/gpu/drm/xen/xen_drm_front_shbuf.h | 72 +++++
4 files changed, 513 insertions(+)
create mode 100644 drivers/gpu/drm/xen/xen_drm_front_shbuf.c
create mode 100644 drivers/gpu/drm/xen/xen_drm_front_shbuf.h

diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
index 8417332f3b58..6c8c751f12ed 100644
--- a/drivers/gpu/drm/xen/Makefile
+++ b/drivers/gpu/drm/xen/Makefile
@@ -2,6 +2,7 @@

drm_xen_front-objs := xen_drm_front.o \
xen_drm_front_evtchnl.o \
+ xen_drm_front_shbuf.o \
xen_drm_front_cfg.o

obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
diff --git a/drivers/gpu/drm/xen/xen_drm_front.c b/drivers/gpu/drm/xen/xen_drm_front.c
index 8312dab862e2..fae631067c31 100644
--- a/drivers/gpu/drm/xen/xen_drm_front.c
+++ b/drivers/gpu/drm/xen/xen_drm_front.c
@@ -18,6 +18,7 @@

#include "xen_drm_front.h"
#include "xen_drm_front_evtchnl.h"
+#include "xen_drm_front_shbuf.h"

static void xen_drv_remove_internal(struct xen_drm_front_info *front_info)
{
@@ -187,6 +188,13 @@ static struct xenbus_driver xen_driver = {

static int __init xen_drv_init(void)
{
+ /* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
+ if (XEN_PAGE_SIZE != PAGE_SIZE) {
+ DRM_ERROR(XENDISPL_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
+ XEN_PAGE_SIZE, PAGE_SIZE);
+ return -ENODEV;
+ }
+
if (!xen_domain())
return -ENODEV;

diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
new file mode 100644
index 000000000000..0fde2d8f7706
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
@@ -0,0 +1,432 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ * Xen para-virtual DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <drm/drmP.h>
+
+#if defined(CONFIG_X86)
+#include <drm/drm_cache.h>
+#endif
+#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/interface/io/displif.h>
+
+#include "xen_drm_front.h"
+#include "xen_drm_front_shbuf.h"
+
+struct xen_drm_front_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_drm_front_shbuf *buf);
+ /* Fill page directory according to para-virtual display protocol. */
+ void (*fill_page_dir)(struct xen_drm_front_shbuf *buf);
+ /* Claim grant references for the pages of the buffer. */
+ int (*grant_refs_for_buffer)(struct xen_drm_front_shbuf *buf,
+ grant_ref_t *priv_gref_head, int gref_idx);
+ /* Map grant references of the buffer. */
+ int (*map)(struct xen_drm_front_shbuf *buf);
+ /* Unmap grant references of the buffer. */
+ int (*unmap)(struct xen_drm_front_shbuf *buf);
+};
+
+grant_ref_t xen_drm_front_shbuf_get_dir_start(struct xen_drm_front_shbuf *buf)
+{
+ if (!buf->grefs)
+ return GRANT_INVALID_REF;
+
+ return buf->grefs[0];
+}
+
+int xen_drm_front_shbuf_map(struct xen_drm_front_shbuf *buf)
+{
+ if (buf->ops->map)
+ return buf->ops->map(buf);
+
+ /* no need to map own grant references */
+ return 0;
+}
+
+int xen_drm_front_shbuf_unmap(struct xen_drm_front_shbuf *buf)
+{
+ if (buf->ops->unmap)
+ return buf->ops->unmap(buf);
+
+ /* no need to unmap own grant references */
+ return 0;
+}
+
+void xen_drm_front_shbuf_flush(struct xen_drm_front_shbuf *buf)
+{
+#if defined(CONFIG_X86)
+ drm_clflush_pages(buf->pages, buf->num_pages);
+#endif
+}
+
+void xen_drm_front_shbuf_free(struct xen_drm_front_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);
+ if (buf->sgt) {
+ sg_free_table(buf->sgt);
+ kvfree(buf->pages);
+ }
+ kfree(buf);
+}
+
+/*
+ * number of grefs a page can hold with respect to the
+ * struct xendispl_page_directory header
+ */
+#define XEN_DRM_NUM_GREFS_PER_PAGE ((PAGE_SIZE - \
+ offsetof(struct xendispl_page_directory, gref)) / \
+ sizeof(grant_ref_t))
+
+static int get_num_pages_dir(struct xen_drm_front_shbuf *buf)
+{
+ /* number of pages the page directory consumes itself */
+ return DIV_ROUND_UP(buf->num_pages, XEN_DRM_NUM_GREFS_PER_PAGE);
+}
+
+static void backend_calc_num_grefs(struct xen_drm_front_shbuf *buf)
+{
+ /* only for pages the page directory consumes itself */
+ buf->num_grefs = get_num_pages_dir(buf);
+}
+
+static void guest_calc_num_grefs(struct xen_drm_front_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) \
+ ((phys_addr_t)pfn_to_kaddr(page_to_xen_pfn(page)))
+
+static int backend_unmap(struct xen_drm_front_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) {
+ DRM_ERROR("Failed to get memory while unmapping\n");
+ 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))
+ DRM_ERROR("Failed to unmap page %d: %d\n",
+ i, unmap_ops[i].status);
+ }
+
+ if (ret)
+ DRM_ERROR("Failed to unmap grant references, ret %d", ret);
+
+ kfree(unmap_ops);
+ kfree(buf->backend_map_handles);
+ buf->backend_map_handles = NULL;
+ return ret;
+}
+
+static int backend_map(struct xen_drm_front_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 xendispl_page_directory *page_dir =
+ (struct xendispl_page_directory *)ptr;
+ int to_copy = XEN_DRM_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))
+ DRM_ERROR("Failed to map page %d: %d\n",
+ cur_page, map_ops[cur_page].status);
+ }
+
+ if (ret) {
+ DRM_ERROR("Failed to map grant references, ret %d", ret);
+ backend_unmap(buf);
+ }
+
+ kfree(map_ops);
+ return ret;
+}
+
+static void backend_fill_page_dir(struct xen_drm_front_shbuf *buf)
+{
+ struct xendispl_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 xendispl_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 xendispl_page_directory *)ptr;
+ page_dir->gref_dir_next_page = GRANT_INVALID_REF;
+}
+
+static void guest_fill_page_dir(struct xen_drm_front_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 xendispl_page_directory *page_dir =
+ (struct xendispl_page_directory *)ptr;
+
+ if (grefs_left <= XEN_DRM_NUM_GREFS_PER_PAGE) {
+ to_copy = grefs_left;
+ page_dir->gref_dir_next_page = GRANT_INVALID_REF;
+ } else {
+ to_copy = XEN_DRM_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;
+ }
+}
+
+static int guest_grant_refs_for_buffer(struct xen_drm_front_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;
+}
+
+static int grant_references(struct xen_drm_front_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) {
+ DRM_ERROR("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;
+}
+
+static int alloc_storage(struct xen_drm_front_shbuf *buf)
+{
+ if (buf->sgt) {
+ buf->pages = kvmalloc_array(buf->num_pages,
+ sizeof(struct page *), GFP_KERNEL);
+ if (!buf->pages)
+ return -ENOMEM;
+
+ if (drm_prime_sg_to_page_addr_arrays(buf->sgt, buf->pages,
+ NULL, buf->num_pages) < 0)
+ return -EINVAL;
+ }
+
+ 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 be allocated buffers we don't need grant_refs_for_buffer as those
+ * grant references are allocated at backend side
+ */
+static const struct xen_drm_front_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_drm_front_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,
+};
+
+struct xen_drm_front_shbuf *xen_drm_front_shbuf_alloc(
+ struct xen_drm_front_shbuf_cfg *cfg)
+{
+ struct xen_drm_front_shbuf *buf;
+ int ret;
+
+ /* either pages or sgt, not both */
+ if (unlikely(cfg->pages && cfg->sgt)) {
+ DRM_ERROR("Cannot handle buffer allocation with both pages and sg table provided\n");
+ return NULL;
+ }
+
+ buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+ if (!buf)
+ return NULL;
+
+ if (cfg->be_alloc)
+ buf->ops = &backend_ops;
+ else
+ buf->ops = &local_ops;
+
+ buf->xb_dev = cfg->xb_dev;
+ buf->num_pages = DIV_ROUND_UP(cfg->size, PAGE_SIZE);
+ buf->sgt = cfg->sgt;
+ 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 buf;
+
+fail:
+ xen_drm_front_shbuf_free(buf);
+ return ERR_PTR(ret);
+}
diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.h b/drivers/gpu/drm/xen/xen_drm_front_shbuf.h
new file mode 100644
index 000000000000..6c4fbc68f328
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ * Xen para-virtual DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_DRM_FRONT_SHBUF_H_
+#define __XEN_DRM_FRONT_SHBUF_H_
+
+#include <linux/kernel.h>
+#include <linux/scatterlist.h>
+
+#include <xen/grant_table.h>
+
+struct xen_drm_front_shbuf {
+ /*
+ * number of references granted for the backend use:
+ * - for allocated/imported dma-buf's this holds number of grant
+ * references for the page directory and pages of the buffer
+ * - for the buffer provided by the backend this holds number of
+ * grant references for the page directory as grant references for
+ * the buffer will be provided by the backend
+ */
+ int num_grefs;
+ grant_ref_t *grefs;
+ unsigned char *directory;
+
+ /*
+ * there are 2 ways to provide backing storage for this shared buffer:
+ * either pages or sgt. if buffer created from sgt then we own
+ * the pages and must free those ourselves on closure
+ */
+ int num_pages;
+ struct page **pages;
+
+ struct sg_table *sgt;
+
+ struct xenbus_device *xb_dev;
+
+ /* these are the ops used internally depending on be_alloc mode */
+ const struct xen_drm_front_shbuf_ops *ops;
+
+ /* Xen map handles for the buffer allocated by the backend */
+ grant_handle_t *backend_map_handles;
+};
+
+struct xen_drm_front_shbuf_cfg {
+ struct xenbus_device *xb_dev;
+ size_t size;
+ struct page **pages;
+ struct sg_table *sgt;
+ bool be_alloc;
+};
+
+struct xen_drm_front_shbuf *xen_drm_front_shbuf_alloc(
+ struct xen_drm_front_shbuf_cfg *cfg);
+
+grant_ref_t xen_drm_front_shbuf_get_dir_start(struct xen_drm_front_shbuf *buf);
+
+int xen_drm_front_shbuf_map(struct xen_drm_front_shbuf *buf);
+
+int xen_drm_front_shbuf_unmap(struct xen_drm_front_shbuf *buf);
+
+void xen_drm_front_shbuf_flush(struct xen_drm_front_shbuf *buf);
+
+void xen_drm_front_shbuf_free(struct xen_drm_front_shbuf *buf);
+
+#endif /* __XEN_DRM_FRONT_SHBUF_H_ */
--
2.7.4
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