unmap_grant_pages() currently waits for the pages to no longer be used. In https://github.com/QubesOS/qubes-issues/issues/7481, this lead to a deadlock against i915: i915 was waiting for gntdev's MMU notifier to finish, while gntdev was waiting for i915 to free its pages. I also believe this is responsible for various deadlocks I have experienced in the past. Avoid these problems by making unmap_grant_pages async. This requires making it return void, as any errors will not be available when the function returns. Fortunately, the only use of the return value is a WARN_ON(), which can be replaced by a WARN_ON when the error is detected. Additionally, a failed call will not prevent further calls from being made, but this is harmless. Because unmap_grant_pages is now async, the grant handle will be sent to INVALID_GRANT_HANDLE too late to prevent multiple unmaps of the same handle. Instead, a separate bool array is allocated for this purpose. This wastes memory, but stuffing this information in padding bytes is too fragile. Furthermore, it is necessary to grab a reference to the map before making the asynchronous call, and release the reference when the call returns. Fixes: 745282256c75 ("xen/gntdev: safely unmap grants in case they are still in use") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx> --- drivers/xen/gntdev-common.h | 5 ++ drivers/xen/gntdev.c | 100 +++++++++++++++++++----------------- 2 files changed, 59 insertions(+), 46 deletions(-) diff --git a/drivers/xen/gntdev-common.h b/drivers/xen/gntdev-common.h index 20d7d059dadb..a268cdb1f7bf 100644 --- a/drivers/xen/gntdev-common.h +++ b/drivers/xen/gntdev-common.h @@ -16,6 +16,7 @@ #include <linux/mmu_notifier.h> #include <linux/types.h> #include <xen/interface/event_channel.h> +#include <xen/grant_table.h> struct gntdev_dmabuf_priv; @@ -56,6 +57,7 @@ struct gntdev_grant_map { struct gnttab_unmap_grant_ref *unmap_ops; struct gnttab_map_grant_ref *kmap_ops; struct gnttab_unmap_grant_ref *kunmap_ops; + bool *being_removed; struct page **pages; unsigned long pages_vm_start; @@ -73,6 +75,9 @@ struct gntdev_grant_map { /* Needed to avoid allocation in gnttab_dma_free_pages(). */ xen_pfn_t *frames; #endif + + /* Needed to avoid allocation in __unmap_grant_pages */ + struct gntab_unmap_queue_data unmap_data; }; struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count, diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 59ffea800079..90bd2b5ef7dd 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -35,6 +35,7 @@ #include <linux/slab.h> #include <linux/highmem.h> #include <linux/refcount.h> +#include <linux/workqueue.h> #include <xen/xen.h> #include <xen/grant_table.h> @@ -62,8 +63,8 @@ MODULE_PARM_DESC(limit, static int use_ptemod; -static int unmap_grant_pages(struct gntdev_grant_map *map, - int offset, int pages); +static void unmap_grant_pages(struct gntdev_grant_map *map, + int offset, int pages); static struct miscdevice gntdev_miscdev; @@ -120,6 +121,7 @@ static void gntdev_free_map(struct gntdev_grant_map *map) kvfree(map->unmap_ops); kvfree(map->kmap_ops); kvfree(map->kunmap_ops); + kvfree(map->being_removed); kfree(map); } @@ -140,10 +142,13 @@ struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count, add->unmap_ops = kvmalloc_array(count, sizeof(add->unmap_ops[0]), GFP_KERNEL); add->pages = kvcalloc(count, sizeof(add->pages[0]), GFP_KERNEL); + add->being_removed = + kvcalloc(count, sizeof(add->being_removed[0]), GFP_KERNEL); if (NULL == add->grants || NULL == add->map_ops || NULL == add->unmap_ops || - NULL == add->pages) + NULL == add->pages || + NULL == add->being_removed) goto err; if (use_ptemod) { add->kmap_ops = kvmalloc_array(count, sizeof(add->kmap_ops[0]), @@ -349,79 +354,84 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map) return err; } -static int __unmap_grant_pages(struct gntdev_grant_map *map, int offset, - int pages) +static void __unmap_grant_pages_done(int result, + struct gntab_unmap_queue_data *data) { - int i, err = 0; - struct gntab_unmap_queue_data unmap_data; - - if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) { - int pgno = (map->notify.addr >> PAGE_SHIFT); - if (pgno >= offset && pgno < offset + pages) { - /* No need for kmap, pages are in lowmem */ - uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno])); - tmp[map->notify.addr & (PAGE_SIZE-1)] = 0; - map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE; - } - } - - unmap_data.unmap_ops = map->unmap_ops + offset; - unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL; - unmap_data.pages = map->pages + offset; - unmap_data.count = pages; - - err = gnttab_unmap_refs_sync(&unmap_data); - if (err) - return err; + unsigned int i; + struct gntdev_grant_map *map = data->data; + unsigned int offset = data->unmap_ops - map->unmap_ops; - for (i = 0; i < pages; i++) { - if (map->unmap_ops[offset+i].status) - err = -EINVAL; + for (i = 0; i < data->count; i++) { + WARN_ON(map->unmap_ops[offset+i].status); pr_debug("unmap handle=%d st=%d\n", map->unmap_ops[offset+i].handle, map->unmap_ops[offset+i].status); map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE; if (use_ptemod) { - if (map->kunmap_ops[offset+i].status) - err = -EINVAL; + WARN_ON(map->kunmap_ops[offset+i].status); pr_debug("kunmap handle=%u st=%d\n", map->kunmap_ops[offset+i].handle, map->kunmap_ops[offset+i].status); map->kunmap_ops[offset+i].handle = INVALID_GRANT_HANDLE; } } - return err; + + /* Release reference taken by __unmap_grant_pages */ + gntdev_put_map(NULL, map); } -static int unmap_grant_pages(struct gntdev_grant_map *map, int offset, - int pages) +static void __unmap_grant_pages(struct gntdev_grant_map *map, int offset, + int pages) +{ + if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) { + int pgno = (map->notify.addr >> PAGE_SHIFT); + + if (pgno >= offset && pgno < offset + pages) { + /* No need for kmap, pages are in lowmem */ + uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno])); + + tmp[map->notify.addr & (PAGE_SIZE-1)] = 0; + map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE; + } + } + + map->unmap_data.unmap_ops = map->unmap_ops + offset; + map->unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL; + map->unmap_data.pages = map->pages + offset; + map->unmap_data.count = pages; + map->unmap_data.done = __unmap_grant_pages_done; + map->unmap_data.data = map; + refcount_inc(&map->users); /* to keep map alive during async call below */ + + gnttab_unmap_refs_async(&map->unmap_data); +} + +static void unmap_grant_pages(struct gntdev_grant_map *map, int offset, + int pages) { - int range, err = 0; + int range; pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages); /* It is possible the requested range will have a "hole" where we * already unmapped some of the grants. Only unmap valid ranges. */ - while (pages && !err) { - while (pages && - map->unmap_ops[offset].handle == INVALID_GRANT_HANDLE) { + while (pages) { + while (pages && map->being_removed[offset]) { offset++; pages--; } range = 0; while (range < pages) { - if (map->unmap_ops[offset + range].handle == - INVALID_GRANT_HANDLE) + if (map->being_removed[offset + range]) break; + map->being_removed[offset + range] = true; range++; } - err = __unmap_grant_pages(map, offset, range); + __unmap_grant_pages(map, offset, range); offset += range; pages -= range; } - - return err; } /* ------------------------------------------------------------------ */ @@ -473,7 +483,6 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn, struct gntdev_grant_map *map = container_of(mn, struct gntdev_grant_map, notifier); unsigned long mstart, mend; - int err; if (!mmu_notifier_range_blockable(range)) return false; @@ -494,10 +503,9 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn, map->index, map->count, map->vma->vm_start, map->vma->vm_end, range->start, range->end, mstart, mend); - err = unmap_grant_pages(map, + unmap_grant_pages(map, (mstart - map->vma->vm_start) >> PAGE_SHIFT, (mend - mstart) >> PAGE_SHIFT); - WARN_ON(err); return true; } -- Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab
