From 4e6fdafa7ac395ad47a80a0e7b4fd1e11550f862 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 7 Mar 2017 12:03:38 +0000 Subject: [PATCH] drm/i915: Use pagecache write to prepopulate shmemfs from pwrite-ioctl Before we instantiate/pin the backing store for our use, we can prepopulate the shmemfs filp efficiently using a write into the pagecache. We avoid the penalty of instantiating all the pages, important if the user is just writing to a few and never uses the object on the GPU, and using a direct write into shmemfs allows it to avoid the cost of retrieving a page (mostly the clear-before-use, but in theory we could curtail swapin) before it is overwritten. This can be extended later to provide additional specialisation for other backends (other than shmemfs). For now it provides a defense against very large write-only allocations from exhausting all of system memory. v2: Smelling fixes. Fixes: fe115628d567 ("drm/i915: Implement pwrite without struct-mutex") References: https://bugs.freedesktop.org/show_bug.cgi?id=99107 Signed-off-by: Chris Wilson Cc: Matthew Auld Cc: Joonas Lahtinen Cc: Mika Kuoppala Cc: # v4.10+ Reviewed-by: Joonas Lahtinen Reviewed-by: Tvrtko Ursulin Link: http://patchwork.freedesktop.org/patch/msgid/20170307120338.7277-2-chris@chris-wilson.co.uk (cherry picked from commit 7c55e2c5772dcf3cbacd0fa2bcfeefae416b73f7) Signed-off-by: Jani Nikula --- drivers/gpu/drm/i915/i915_gem.c | 78 ++++++++++++++++++++++++++++++++++ drivers/gpu/drm/i915/i915_gem_object.h | 3 ++ 2 files changed, 81 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 3591e86..10777da 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1434,6 +1434,12 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data, trace_i915_gem_object_pwrite(obj, args->offset, args->size); + ret = -ENODEV; + if (obj->ops->pwrite) + ret = obj->ops->pwrite(obj, args); + if (ret != -ENODEV) + goto err; + ret = i915_gem_object_wait(obj, I915_WAIT_INTERRUPTIBLE | I915_WAIT_ALL, @@ -2566,6 +2572,75 @@ err_unlock: goto out_unlock; } +static int +i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj, + const struct drm_i915_gem_pwrite *arg) +{ + struct address_space *mapping = obj->base.filp->f_mapping; + char __user *user_data = u64_to_user_ptr(arg->data_ptr); + u64 remain, offset; + unsigned int pg; + + /* Before we instantiate/pin the backing store for our use, we + * can prepopulate the shmemfs filp efficiently using a write into + * the pagecache. We avoid the penalty of instantiating all the + * pages, important if the user is just writing to a few and never + * uses the object on the GPU, and using a direct write into shmemfs + * allows it to avoid the cost of retrieving a page (either swapin + * or clearing-before-use) before it is overwritten. + */ + if (READ_ONCE(obj->mm.pages)) + return -ENODEV; + + /* Before the pages are instantiated the object is treated as being + * in the CPU domain. The pages will be clflushed as required before + * use, and we can freely write into the pages directly. If userspace + * races pwrite with any other operation; corruption will ensue - + * that is userspace's prerogative! + */ + + remain = arg->size; + offset = arg->offset; + pg = offset_in_page(offset); + + do { + unsigned int len, unwritten; + struct page *page; + void *data, *vaddr; + int err; + + len = PAGE_SIZE - pg; + if (len > remain) + len = remain; + + err = pagecache_write_begin(obj->base.filp, mapping, + offset, len, 0, + &page, &data); + if (err < 0) + return err; + + vaddr = kmap(page); + unwritten = copy_from_user(vaddr + pg, user_data, len); + kunmap(page); + + err = pagecache_write_end(obj->base.filp, mapping, + offset, len, len - unwritten, + page, data); + if (err < 0) + return err; + + if (unwritten) + return -EFAULT; + + remain -= len; + user_data += len; + offset += len; + pg = 0; + } while (remain); + + return 0; +} + static bool ban_context(const struct i915_gem_context *ctx) { return (i915_gem_context_is_bannable(ctx) && @@ -3987,8 +4062,11 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj, static const struct drm_i915_gem_object_ops i915_gem_object_ops = { .flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE | I915_GEM_OBJECT_IS_SHRINKABLE, + .get_pages = i915_gem_object_get_pages_gtt, .put_pages = i915_gem_object_put_pages_gtt, + + .pwrite = i915_gem_object_pwrite_gtt, }; struct drm_i915_gem_object * diff --git a/drivers/gpu/drm/i915/i915_gem_object.h b/drivers/gpu/drm/i915/i915_gem_object.h index bf90b07..76b80a0 100644 --- a/drivers/gpu/drm/i915/i915_gem_object.h +++ b/drivers/gpu/drm/i915/i915_gem_object.h @@ -54,6 +54,9 @@ struct drm_i915_gem_object_ops { struct sg_table *(*get_pages)(struct drm_i915_gem_object *); void (*put_pages)(struct drm_i915_gem_object *, struct sg_table *); + int (*pwrite)(struct drm_i915_gem_object *, + const struct drm_i915_gem_pwrite *); + int (*dmabuf_export)(struct drm_i915_gem_object *); void (*release)(struct drm_i915_gem_object *); }; -- 2.7.4