commit dbe97cff7dd9f0f75c524afdd55ad46be3d15295 upstream
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.
It is also necessary to guard against reentrancy in gntdev_map_put(), and to handle the case where userspace tries to map a mapping whose contents have not all been freed yet.
Fixes: 745282256c75 ("xen/gntdev: safely unmap grants in case they are still in use") Cc: stable@vger.kernel.org Signed-off-by: Demi Marie Obenour demi@invisiblethingslab.com Reviewed-by: Juergen Gross jgross@suse.com Link: https://lore.kernel.org/r/20220622022726.2538-1-demi@invisiblethingslab.com Signed-off-by: Juergen Gross jgross@suse.com --- drivers/xen/gntdev.c | 144 ++++++++++++++++++++++++++++++------------- 1 file changed, 102 insertions(+), 42 deletions(-)
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 69d59102ff1b..2c3248e71e9c 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -57,6 +57,7 @@ MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
static atomic_t pages_mapped = ATOMIC_INIT(0);
+/* True in PV mode, false otherwise */ static int use_ptemod; #define populate_freeable_maps use_ptemod
@@ -92,11 +93,16 @@ struct 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; + /* Number of live grants */ + atomic_t live_grants; + /* Needed to avoid allocation in unmap_grant_pages */ + struct gntab_unmap_queue_data unmap_data; };
-static int unmap_grant_pages(struct grant_map *map, int offset, int pages); +static void unmap_grant_pages(struct grant_map *map, int offset, int pages);
/* ------------------------------------------------------------------ */
@@ -127,6 +133,7 @@ static void gntdev_free_map(struct grant_map *map) kfree(map->unmap_ops); kfree(map->kmap_ops); kfree(map->kunmap_ops); + kfree(map->being_removed); kfree(map); }
@@ -145,12 +152,15 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count) add->kmap_ops = kcalloc(count, sizeof(add->kmap_ops[0]), GFP_KERNEL); add->kunmap_ops = kcalloc(count, sizeof(add->kunmap_ops[0]), GFP_KERNEL); add->pages = kcalloc(count, sizeof(add->pages[0]), GFP_KERNEL); + add->being_removed = + kcalloc(count, sizeof(add->being_removed[0]), GFP_KERNEL); if (NULL == add->grants || NULL == add->map_ops || NULL == add->unmap_ops || NULL == add->kmap_ops || NULL == add->kunmap_ops || - NULL == add->pages) + NULL == add->pages || + NULL == add->being_removed) goto err;
if (gnttab_alloc_pages(count, add->pages)) @@ -215,6 +225,34 @@ static void gntdev_put_map(struct gntdev_priv *priv, struct grant_map *map) return;
atomic_sub(map->count, &pages_mapped); + if (map->pages && !use_ptemod) { + /* + * Increment the reference count. This ensures that the + * subsequent call to unmap_grant_pages() will not wind up + * re-entering itself. It *can* wind up calling + * gntdev_put_map() recursively, but such calls will be with a + * reference count greater than 1, so they will return before + * this code is reached. The recursion depth is thus limited to + * 1. + */ + atomic_set(&map->users, 1); + + /* + * Unmap the grants. This may or may not be asynchronous, so it + * is possible that the reference count is 1 on return, but it + * could also be greater than 1. + */ + unmap_grant_pages(map, 0, map->count); + + /* Check if the memory now needs to be freed */ + if (!atomic_dec_and_test(&map->users)) + return; + + /* + * All pages have been returned to the hypervisor, so free the + * map. + */ + }
if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { notify_remote_via_evtchn(map->notify.event); @@ -272,6 +310,7 @@ static int set_grant_ptes_as_special(pte_t *pte, pgtable_t token,
static int map_grant_pages(struct grant_map *map) { + size_t alloced = 0; int i, err = 0;
if (!use_ptemod) { @@ -320,85 +359,107 @@ static int map_grant_pages(struct grant_map *map) map->pages, map->count);
for (i = 0; i < map->count; i++) { - if (map->map_ops[i].status == GNTST_okay) + if (map->map_ops[i].status == GNTST_okay) { map->unmap_ops[i].handle = map->map_ops[i].handle; - else if (!err) + if (!use_ptemod) + alloced++; + } else if (!err) err = -EINVAL;
if (map->flags & GNTMAP_device_map) map->unmap_ops[i].dev_bus_addr = map->map_ops[i].dev_bus_addr;
if (use_ptemod) { - if (map->kmap_ops[i].status == GNTST_okay) + if (map->kmap_ops[i].status == GNTST_okay) { + if (map->map_ops[i].status == GNTST_okay) + alloced++; map->kunmap_ops[i].handle = map->kmap_ops[i].handle; - else if (!err) + } else if (!err) err = -EINVAL; } } + atomic_add(alloced, &map->live_grants); return err; }
-static int __unmap_grant_pages(struct 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; + unsigned int i; + struct grant_map *map = data->data; + unsigned int offset = data->unmap_ops - map->unmap_ops; + + 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 = -1; + } + /* + * Decrease the live-grant counter. This must happen after the loop to + * prevent premature reuse of the grants by gnttab_mmap(). + */ + atomic_sub(data->count, &map->live_grants);
+ /* Release reference taken by unmap_grant_pages */ + gntdev_put_map(NULL, map); +} + +static void __unmap_grant_pages(struct 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; } }
- 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; + 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; + atomic_inc(&map->users); /* to keep map alive during async call below */
- err = gnttab_unmap_refs_sync(&unmap_data); - if (err) - return err; - - for (i = 0; i < pages; i++) { - if (map->unmap_ops[offset+i].status) - err = -EINVAL; - 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 = -1; - } - return err; + gnttab_unmap_refs_async(&map->unmap_data); }
-static int unmap_grant_pages(struct grant_map *map, int offset, int pages) +static void unmap_grant_pages(struct grant_map *map, int offset, int pages) { - int range, err = 0; + int range; + + if (atomic_read(&map->live_grants) == 0) + return; /* Nothing to do */
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 == -1) { + while (pages) { + while (pages && map->being_removed[offset]) { offset++; pages--; } range = 0; while (range < pages) { - if (map->unmap_ops[offset+range].handle == -1) + if (map->being_removed[offset + range]) break; + map->being_removed[offset + range] = true; range++; } - err = __unmap_grant_pages(map, offset, range); + if (range) + __unmap_grant_pages(map, offset, range); offset += range; pages -= range; } - - return err; }
/* ------------------------------------------------------------------ */ @@ -454,7 +515,6 @@ static void unmap_if_in_range(struct grant_map *map, unsigned long start, unsigned long end) { unsigned long mstart, mend; - int err;
if (!map->vma) return; @@ -468,10 +528,9 @@ static void unmap_if_in_range(struct grant_map *map, map->index, map->count, map->vma->vm_start, map->vma->vm_end, start, 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); }
static void mn_invl_range_start(struct mmu_notifier *mn, @@ -503,7 +562,6 @@ static void mn_release(struct mmu_notifier *mn, { struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn); struct grant_map *map; - int err;
mutex_lock(&priv->lock); list_for_each_entry(map, &priv->maps, next) { @@ -512,8 +570,7 @@ static void mn_release(struct mmu_notifier *mn, pr_debug("map %d+%d (%lx %lx)\n", map->index, map->count, map->vma->vm_start, map->vma->vm_end); - err = unmap_grant_pages(map, /* offset */ 0, map->count); - WARN_ON(err); + unmap_grant_pages(map, /* offset */ 0, map->count); } list_for_each_entry(map, &priv->freeable_maps, next) { if (!map->vma) @@ -521,8 +578,7 @@ static void mn_release(struct mmu_notifier *mn, pr_debug("map %d+%d (%lx %lx)\n", map->index, map->count, map->vma->vm_start, map->vma->vm_end); - err = unmap_grant_pages(map, /* offset */ 0, map->count); - WARN_ON(err); + unmap_grant_pages(map, /* offset */ 0, map->count); } mutex_unlock(&priv->lock); } @@ -1012,6 +1068,10 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma) goto unlock_out; }
+ if (atomic_read(&map->live_grants)) { + err = -EAGAIN; + goto unlock_out; + } atomic_inc(&map->users);
vma->vm_ops = &gntdev_vmops;