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xen/gntdev: Avoid blocking in unmap_grant_pages()
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: 745282256c ("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>
This commit is contained in:
Demi Marie Obenour
Juergen Gross
parent
ca6969013d
commit
dbe97cff7d
2 changed files with 113 additions and 51 deletions
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@ -16,6 +16,7 @@
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#include <linux/mmu_notifier.h>
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#include <linux/types.h>
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#include <xen/interface/event_channel.h>
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#include <xen/grant_table.h>
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struct gntdev_dmabuf_priv;
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@ -56,6 +57,7 @@ struct gntdev_grant_map {
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struct gnttab_unmap_grant_ref *unmap_ops;
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struct gnttab_map_grant_ref *kmap_ops;
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struct gnttab_unmap_grant_ref *kunmap_ops;
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bool *being_removed;
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struct page **pages;
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unsigned long pages_vm_start;
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@ -73,6 +75,11 @@ struct gntdev_grant_map {
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/* Needed to avoid allocation in gnttab_dma_free_pages(). */
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xen_pfn_t *frames;
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#endif
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/* Number of live grants */
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atomic_t live_grants;
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/* Needed to avoid allocation in __unmap_grant_pages */
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struct gntab_unmap_queue_data unmap_data;
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};
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struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,
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@ -35,6 +35,7 @@
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#include <linux/slab.h>
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#include <linux/highmem.h>
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#include <linux/refcount.h>
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#include <linux/workqueue.h>
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#include <xen/xen.h>
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#include <xen/grant_table.h>
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@ -60,10 +61,11 @@ module_param(limit, uint, 0644);
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MODULE_PARM_DESC(limit,
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"Maximum number of grants that may be mapped by one mapping request");
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/* True in PV mode, false otherwise */
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static int use_ptemod;
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static int unmap_grant_pages(struct gntdev_grant_map *map,
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int offset, int pages);
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static void unmap_grant_pages(struct gntdev_grant_map *map,
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int offset, int pages);
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static struct miscdevice gntdev_miscdev;
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@ -120,6 +122,7 @@ static void gntdev_free_map(struct gntdev_grant_map *map)
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kvfree(map->unmap_ops);
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kvfree(map->kmap_ops);
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kvfree(map->kunmap_ops);
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kvfree(map->being_removed);
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kfree(map);
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}
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@ -140,10 +143,13 @@ struct gntdev_grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,
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add->unmap_ops = kvmalloc_array(count, sizeof(add->unmap_ops[0]),
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GFP_KERNEL);
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add->pages = kvcalloc(count, sizeof(add->pages[0]), GFP_KERNEL);
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add->being_removed =
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kvcalloc(count, sizeof(add->being_removed[0]), GFP_KERNEL);
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if (NULL == add->grants ||
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NULL == add->map_ops ||
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NULL == add->unmap_ops ||
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NULL == add->pages)
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NULL == add->pages ||
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NULL == add->being_removed)
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goto err;
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if (use_ptemod) {
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add->kmap_ops = kvmalloc_array(count, sizeof(add->kmap_ops[0]),
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@ -250,9 +256,36 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map)
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if (!refcount_dec_and_test(&map->users))
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return;
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if (map->pages && !use_ptemod)
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if (map->pages && !use_ptemod) {
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/*
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* Increment the reference count. This ensures that the
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* subsequent call to unmap_grant_pages() will not wind up
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* re-entering itself. It *can* wind up calling
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* gntdev_put_map() recursively, but such calls will be with a
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* reference count greater than 1, so they will return before
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* this code is reached. The recursion depth is thus limited to
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* 1. Do NOT use refcount_inc() here, as it will detect that
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* the reference count is zero and WARN().
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*/
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refcount_set(&map->users, 1);
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/*
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* Unmap the grants. This may or may not be asynchronous, so it
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* is possible that the reference count is 1 on return, but it
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* could also be greater than 1.
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*/
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unmap_grant_pages(map, 0, map->count);
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/* Check if the memory now needs to be freed */
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if (!refcount_dec_and_test(&map->users))
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return;
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/*
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* All pages have been returned to the hypervisor, so free the
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* map.
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*/
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}
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if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
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notify_remote_via_evtchn(map->notify.event);
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evtchn_put(map->notify.event);
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@ -283,6 +316,7 @@ static int find_grant_ptes(pte_t *pte, unsigned long addr, void *data)
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int gntdev_map_grant_pages(struct gntdev_grant_map *map)
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{
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size_t alloced = 0;
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int i, err = 0;
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if (!use_ptemod) {
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@ -331,97 +365,116 @@ int gntdev_map_grant_pages(struct gntdev_grant_map *map)
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map->count);
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for (i = 0; i < map->count; i++) {
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if (map->map_ops[i].status == GNTST_okay)
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if (map->map_ops[i].status == GNTST_okay) {
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map->unmap_ops[i].handle = map->map_ops[i].handle;
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else if (!err)
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if (!use_ptemod)
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alloced++;
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} else if (!err)
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err = -EINVAL;
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if (map->flags & GNTMAP_device_map)
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map->unmap_ops[i].dev_bus_addr = map->map_ops[i].dev_bus_addr;
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if (use_ptemod) {
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if (map->kmap_ops[i].status == GNTST_okay)
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if (map->kmap_ops[i].status == GNTST_okay) {
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if (map->map_ops[i].status == GNTST_okay)
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alloced++;
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map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
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else if (!err)
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} else if (!err)
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err = -EINVAL;
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}
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}
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atomic_add(alloced, &map->live_grants);
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return err;
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}
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static int __unmap_grant_pages(struct gntdev_grant_map *map, int offset,
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int pages)
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static void __unmap_grant_pages_done(int result,
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struct gntab_unmap_queue_data *data)
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{
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int i, err = 0;
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struct gntab_unmap_queue_data unmap_data;
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unsigned int i;
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struct gntdev_grant_map *map = data->data;
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unsigned int offset = data->unmap_ops - map->unmap_ops;
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if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
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int pgno = (map->notify.addr >> PAGE_SHIFT);
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if (pgno >= offset && pgno < offset + pages) {
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/* No need for kmap, pages are in lowmem */
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uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
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tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
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map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
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}
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}
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unmap_data.unmap_ops = map->unmap_ops + offset;
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unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
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unmap_data.pages = map->pages + offset;
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unmap_data.count = pages;
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err = gnttab_unmap_refs_sync(&unmap_data);
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if (err)
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return err;
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for (i = 0; i < pages; i++) {
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if (map->unmap_ops[offset+i].status)
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err = -EINVAL;
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for (i = 0; i < data->count; i++) {
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WARN_ON(map->unmap_ops[offset+i].status);
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pr_debug("unmap handle=%d st=%d\n",
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map->unmap_ops[offset+i].handle,
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map->unmap_ops[offset+i].status);
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map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
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if (use_ptemod) {
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if (map->kunmap_ops[offset+i].status)
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err = -EINVAL;
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WARN_ON(map->kunmap_ops[offset+i].status);
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pr_debug("kunmap handle=%u st=%d\n",
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map->kunmap_ops[offset+i].handle,
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map->kunmap_ops[offset+i].status);
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map->kunmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
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}
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}
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return err;
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/*
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* Decrease the live-grant counter. This must happen after the loop to
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* prevent premature reuse of the grants by gnttab_mmap().
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*/
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atomic_sub(data->count, &map->live_grants);
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/* Release reference taken by __unmap_grant_pages */
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gntdev_put_map(NULL, map);
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}
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static int unmap_grant_pages(struct gntdev_grant_map *map, int offset,
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int pages)
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static void __unmap_grant_pages(struct gntdev_grant_map *map, int offset,
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int pages)
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{
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int range, err = 0;
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if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
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int pgno = (map->notify.addr >> PAGE_SHIFT);
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if (pgno >= offset && pgno < offset + pages) {
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/* No need for kmap, pages are in lowmem */
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uint8_t *tmp = pfn_to_kaddr(page_to_pfn(map->pages[pgno]));
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tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
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map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
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}
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}
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map->unmap_data.unmap_ops = map->unmap_ops + offset;
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map->unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
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map->unmap_data.pages = map->pages + offset;
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map->unmap_data.count = pages;
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map->unmap_data.done = __unmap_grant_pages_done;
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map->unmap_data.data = map;
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refcount_inc(&map->users); /* to keep map alive during async call below */
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gnttab_unmap_refs_async(&map->unmap_data);
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}
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static void unmap_grant_pages(struct gntdev_grant_map *map, int offset,
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int pages)
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{
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int range;
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if (atomic_read(&map->live_grants) == 0)
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return; /* Nothing to do */
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pr_debug("unmap %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
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/* It is possible the requested range will have a "hole" where we
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* already unmapped some of the grants. Only unmap valid ranges.
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*/
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while (pages && !err) {
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while (pages &&
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map->unmap_ops[offset].handle == INVALID_GRANT_HANDLE) {
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while (pages) {
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while (pages && map->being_removed[offset]) {
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offset++;
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pages--;
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}
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range = 0;
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while (range < pages) {
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if (map->unmap_ops[offset + range].handle ==
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INVALID_GRANT_HANDLE)
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if (map->being_removed[offset + range])
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break;
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map->being_removed[offset + range] = true;
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range++;
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}
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err = __unmap_grant_pages(map, offset, range);
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if (range)
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__unmap_grant_pages(map, offset, range);
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offset += range;
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pages -= range;
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}
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return err;
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}
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/* ------------------------------------------------------------------ */
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@ -473,7 +526,6 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn,
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struct gntdev_grant_map *map =
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container_of(mn, struct gntdev_grant_map, notifier);
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unsigned long mstart, mend;
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int err;
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if (!mmu_notifier_range_blockable(range))
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return false;
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@ -494,10 +546,9 @@ static bool gntdev_invalidate(struct mmu_interval_notifier *mn,
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map->index, map->count,
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map->vma->vm_start, map->vma->vm_end,
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range->start, range->end, mstart, mend);
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err = unmap_grant_pages(map,
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unmap_grant_pages(map,
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(mstart - map->vma->vm_start) >> PAGE_SHIFT,
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(mend - mstart) >> PAGE_SHIFT);
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WARN_ON(err);
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return true;
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}
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@ -985,6 +1036,10 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
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goto unlock_out;
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if (use_ptemod && map->vma)
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goto unlock_out;
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if (atomic_read(&map->live_grants)) {
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err = -EAGAIN;
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goto unlock_out;
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}
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refcount_inc(&map->users);
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vma->vm_ops = &gntdev_vmops;
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