dbe97cff7d
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>
97 lines
2.4 KiB
C
97 lines
2.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Common functionality of grant device.
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*
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* Copyright (c) 2006-2007, D G Murray.
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* (c) 2009 Gerd Hoffmann <kraxel@redhat.com>
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* (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
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*/
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#ifndef _GNTDEV_COMMON_H
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#define _GNTDEV_COMMON_H
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#include <linux/mm.h>
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#include <linux/mman.h>
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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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struct gntdev_priv {
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/* Maps with visible offsets in the file descriptor. */
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struct list_head maps;
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/* lock protects maps and freeable_maps. */
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struct mutex lock;
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#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
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/* Device for which DMA memory is allocated. */
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struct device *dma_dev;
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#endif
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#ifdef CONFIG_XEN_GNTDEV_DMABUF
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struct gntdev_dmabuf_priv *dmabuf_priv;
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#endif
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};
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struct gntdev_unmap_notify {
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int flags;
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/* Address relative to the start of the gntdev_grant_map. */
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int addr;
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evtchn_port_t event;
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};
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struct gntdev_grant_map {
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struct mmu_interval_notifier notifier;
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struct list_head next;
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struct vm_area_struct *vma;
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int index;
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int count;
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int flags;
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refcount_t users;
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struct gntdev_unmap_notify notify;
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struct ioctl_gntdev_grant_ref *grants;
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struct gnttab_map_grant_ref *map_ops;
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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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#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
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/*
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* If dmabuf_vaddr is not NULL then this mapping is backed by DMA
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* capable memory.
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*/
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struct device *dma_dev;
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/* Flags used to create this DMA buffer: GNTDEV_DMA_FLAG_XXX. */
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int dma_flags;
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void *dma_vaddr;
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dma_addr_t dma_bus_addr;
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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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int dma_flags);
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void gntdev_add_map(struct gntdev_priv *priv, struct gntdev_grant_map *add);
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void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map);
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bool gntdev_test_page_count(unsigned int count);
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int gntdev_map_grant_pages(struct gntdev_grant_map *map);
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#endif
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