Jason Gunthorpe
2019-Oct-28 20:10 UTC
[Nouveau] [PATCH v2 09/15] xen/gntdev: use mmu_range_notifier_insert
From: Jason Gunthorpe <jgg at mellanox.com>
gntdev simply wants to monitor a specific VMA for any notifier events,
this can be done straightforwardly using mmu_range_notifier_insert() over
the VMA's VA range.
The notifier should be attached until the original VMA is destroyed.
It is unclear if any of this is even sane, but at least a lot of duplicate
code is removed.
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko at epam.com>
Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Cc: xen-devel at lists.xenproject.org
Cc: Juergen Gross <jgross at suse.com>
Cc: Stefano Stabellini <sstabellini at kernel.org>
Signed-off-by: Jason Gunthorpe <jgg at mellanox.com>
---
drivers/xen/gntdev-common.h | 8 +-
drivers/xen/gntdev.c | 180 ++++++++++--------------------------
2 files changed, 49 insertions(+), 139 deletions(-)
diff --git a/drivers/xen/gntdev-common.h b/drivers/xen/gntdev-common.h
index 2f8b949c3eeb14..b201fdd20b667b 100644
--- a/drivers/xen/gntdev-common.h
+++ b/drivers/xen/gntdev-common.h
@@ -21,15 +21,8 @@ struct gntdev_dmabuf_priv;
struct gntdev_priv {
/* Maps with visible offsets in the file descriptor. */
struct list_head maps;
- /*
- * Maps that are not visible; will be freed on munmap.
- * Only populated if populate_freeable_maps == 1
- */
- struct list_head freeable_maps;
/* lock protects maps and freeable_maps. */
struct mutex lock;
- struct mm_struct *mm;
- struct mmu_notifier mn;
#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
/* Device for which DMA memory is allocated. */
@@ -49,6 +42,7 @@ struct gntdev_unmap_notify {
};
struct gntdev_grant_map {
+ struct mmu_range_notifier notifier;
struct list_head next;
struct vm_area_struct *vma;
int index;
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index a446a7221e13e9..12d626670bebbc 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -65,7 +65,6 @@ MODULE_PARM_DESC(limit, "Maximum number of grants that
may be mapped by "
static atomic_t pages_mapped = ATOMIC_INIT(0);
static int use_ptemod;
-#define populate_freeable_maps use_ptemod
static int unmap_grant_pages(struct gntdev_grant_map *map,
int offset, int pages);
@@ -251,12 +250,6 @@ void gntdev_put_map(struct gntdev_priv *priv, struct
gntdev_grant_map *map)
evtchn_put(map->notify.event);
}
- if (populate_freeable_maps && priv) {
- mutex_lock(&priv->lock);
- list_del(&map->next);
- mutex_unlock(&priv->lock);
- }
-
if (map->pages && !use_ptemod)
unmap_grant_pages(map, 0, map->count);
gntdev_free_map(map);
@@ -445,17 +438,9 @@ static void gntdev_vma_close(struct vm_area_struct *vma)
struct gntdev_priv *priv = file->private_data;
pr_debug("gntdev_vma_close %p\n", vma);
- if (use_ptemod) {
- /* It is possible that an mmu notifier could be running
- * concurrently, so take priv->lock to ensure that the vma won't
- * vanishing during the unmap_grant_pages call, since we will
- * spin here until that completes. Such a concurrent call will
- * not do any unmapping, since that has been done prior to
- * closing the vma, but it may still iterate the unmap_ops list.
- */
- mutex_lock(&priv->lock);
+ if (use_ptemod && map->vma == vma) {
+ mmu_range_notifier_remove(&map->notifier);
map->vma = NULL;
- mutex_unlock(&priv->lock);
}
vma->vm_private_data = NULL;
gntdev_put_map(priv, map);
@@ -477,109 +462,44 @@ static const struct vm_operations_struct gntdev_vmops = {
/* ------------------------------------------------------------------ */
-static bool in_range(struct gntdev_grant_map *map,
- unsigned long start, unsigned long end)
-{
- if (!map->vma)
- return false;
- if (map->vma->vm_start >= end)
- return false;
- if (map->vma->vm_end <= start)
- return false;
-
- return true;
-}
-
-static int unmap_if_in_range(struct gntdev_grant_map *map,
- unsigned long start, unsigned long end,
- bool blockable)
+static bool gntdev_invalidate(struct mmu_range_notifier *mn,
+ const struct mmu_notifier_range *range,
+ unsigned long cur_seq)
{
+ struct gntdev_grant_map *map + container_of(mn, struct gntdev_grant_map,
notifier);
unsigned long mstart, mend;
int err;
- if (!in_range(map, start, end))
- return 0;
+ if (!mmu_notifier_range_blockable(range))
+ return false;
- if (!blockable)
- return -EAGAIN;
+ /*
+ * If the VMA is split or otherwise changed the notifier is not
+ * updated, but we don't want to process VA's outside the modified
+ * VMA. FIXME: It would be much more understandable to just prevent
+ * modifying the VMA in the first place.
+ */
+ if (map->vma->vm_start >= range->end ||
+ map->vma->vm_end <= range->start)
+ return true;
- mstart = max(start, map->vma->vm_start);
- mend = min(end, map->vma->vm_end);
+ mstart = max(range->start, map->vma->vm_start);
+ mend = min(range->end, map->vma->vm_end);
pr_debug("map %d+%d (%lx %lx), range %lx %lx, mrange %lx %lx\n",
map->index, map->count,
map->vma->vm_start, map->vma->vm_end,
- start, end, mstart, mend);
+ range->start, range->end, mstart, mend);
err = unmap_grant_pages(map,
(mstart - map->vma->vm_start) >> PAGE_SHIFT,
(mend - mstart) >> PAGE_SHIFT);
WARN_ON(err);
- return 0;
-}
-
-static int mn_invl_range_start(struct mmu_notifier *mn,
- const struct mmu_notifier_range *range)
-{
- struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
- struct gntdev_grant_map *map;
- int ret = 0;
-
- if (mmu_notifier_range_blockable(range))
- mutex_lock(&priv->lock);
- else if (!mutex_trylock(&priv->lock))
- return -EAGAIN;
-
- list_for_each_entry(map, &priv->maps, next) {
- ret = unmap_if_in_range(map, range->start, range->end,
- mmu_notifier_range_blockable(range));
- if (ret)
- goto out_unlock;
- }
- list_for_each_entry(map, &priv->freeable_maps, next) {
- ret = unmap_if_in_range(map, range->start, range->end,
- mmu_notifier_range_blockable(range));
- if (ret)
- goto out_unlock;
- }
-
-out_unlock:
- mutex_unlock(&priv->lock);
-
- return ret;
-}
-
-static void mn_release(struct mmu_notifier *mn,
- struct mm_struct *mm)
-{
- struct gntdev_priv *priv = container_of(mn, struct gntdev_priv, mn);
- struct gntdev_grant_map *map;
- int err;
-
- mutex_lock(&priv->lock);
- list_for_each_entry(map, &priv->maps, next) {
- if (!map->vma)
- continue;
- 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);
- }
- list_for_each_entry(map, &priv->freeable_maps, next) {
- if (!map->vma)
- continue;
- 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);
- }
- mutex_unlock(&priv->lock);
+ return true;
}
-static const struct mmu_notifier_ops gntdev_mmu_ops = {
- .release = mn_release,
- .invalidate_range_start = mn_invl_range_start,
+static const struct mmu_range_notifier_ops gntdev_mmu_ops = {
+ .invalidate = gntdev_invalidate,
};
/* ------------------------------------------------------------------ */
@@ -594,7 +514,6 @@ static int gntdev_open(struct inode *inode, struct file
*flip)
return -ENOMEM;
INIT_LIST_HEAD(&priv->maps);
- INIT_LIST_HEAD(&priv->freeable_maps);
mutex_init(&priv->lock);
#ifdef CONFIG_XEN_GNTDEV_DMABUF
@@ -606,17 +525,6 @@ static int gntdev_open(struct inode *inode, struct file
*flip)
}
#endif
- if (use_ptemod) {
- priv->mm = get_task_mm(current);
- if (!priv->mm) {
- kfree(priv);
- return -ENOMEM;
- }
- priv->mn.ops = &gntdev_mmu_ops;
- ret = mmu_notifier_register(&priv->mn, priv->mm);
- mmput(priv->mm);
- }
-
if (ret) {
kfree(priv);
return ret;
@@ -653,16 +561,12 @@ static int gntdev_release(struct inode *inode, struct file
*flip)
list_del(&map->next);
gntdev_put_map(NULL /* already removed */, map);
}
- WARN_ON(!list_empty(&priv->freeable_maps));
mutex_unlock(&priv->lock);
#ifdef CONFIG_XEN_GNTDEV_DMABUF
gntdev_dmabuf_fini(priv->dmabuf_priv);
#endif
- if (use_ptemod)
- mmu_notifier_unregister(&priv->mn, priv->mm);
-
kfree(priv);
return 0;
}
@@ -723,8 +627,6 @@ static long gntdev_ioctl_unmap_grant_ref(struct gntdev_priv
*priv,
map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
if (map) {
list_del(&map->next);
- if (populate_freeable_maps)
- list_add_tail(&map->next, &priv->freeable_maps);
err = 0;
}
mutex_unlock(&priv->lock);
@@ -1096,11 +998,6 @@ static int gntdev_mmap(struct file *flip, struct
vm_area_struct *vma)
goto unlock_out;
if (use_ptemod && map->vma)
goto unlock_out;
- if (use_ptemod && priv->mm != vma->vm_mm) {
- pr_warn("Huh? Other mm?\n");
- goto unlock_out;
- }
-
refcount_inc(&map->users);
vma->vm_ops = &gntdev_vmops;
@@ -1111,10 +1008,6 @@ static int gntdev_mmap(struct file *flip, struct
vm_area_struct *vma)
vma->vm_flags |= VM_DONTCOPY;
vma->vm_private_data = map;
-
- if (use_ptemod)
- map->vma = vma;
-
if (map->flags) {
if ((vma->vm_flags & VM_WRITE) &&
(map->flags & GNTMAP_readonly))
@@ -1125,8 +1018,28 @@ static int gntdev_mmap(struct file *flip, struct
vm_area_struct *vma)
map->flags |= GNTMAP_readonly;
}
+ if (use_ptemod) {
+ map->vma = vma;
+ err = mmu_range_notifier_insert_locked(
+ &map->notifier, vma->vm_start,
+ vma->vm_end - vma->vm_start, vma->vm_mm);
+ if (err)
+ goto out_unlock_put;
+ }
mutex_unlock(&priv->lock);
+ /*
+ * gntdev takes the address of the PTE in find_grant_ptes() and passes
+ * it to the hypervisor in gntdev_map_grant_pages(). The purpose of
+ * the notifier is to prevent the hypervisor pointer to the PTE from
+ * going stale.
+ *
+ * Since this vma's mappings can't be touched without the mmap_sem,
+ * and we are holding it now, there is no need for the notifier_range
+ * locking pattern.
+ */
+ mmu_range_read_begin(&map->notifier);
+
if (use_ptemod) {
map->pages_vm_start = vma->vm_start;
err = apply_to_page_range(vma->vm_mm, vma->vm_start,
@@ -1175,8 +1088,11 @@ static int gntdev_mmap(struct file *flip, struct
vm_area_struct *vma)
mutex_unlock(&priv->lock);
out_put_map:
if (use_ptemod) {
- map->vma = NULL;
unmap_grant_pages(map, 0, map->count);
+ if (map->vma) {
+ mmu_range_notifier_remove(&map->notifier);
+ map->vma = NULL;
+ }
}
gntdev_put_map(priv, map);
return err;
--
2.23.0
Jason Gunthorpe
2019-Nov-01 17:48 UTC
[Nouveau] [PATCH v2 09/15] xen/gntdev: use mmu_range_notifier_insert
On Wed, Oct 30, 2019 at 12:55:37PM -0400, Boris Ostrovsky wrote:> On 10/28/19 4:10 PM, Jason Gunthorpe wrote: > > From: Jason Gunthorpe <jgg at mellanox.com> > > > > gntdev simply wants to monitor a specific VMA for any notifier events, > > this can be done straightforwardly using mmu_range_notifier_insert() over > > the VMA's VA range. > > > > The notifier should be attached until the original VMA is destroyed. > > > > It is unclear if any of this is even sane, but at least a lot of duplicate > > code is removed. > > I didn't have a chance to look at the patch itself yet but as a heads-up > --- it crashes dom0.Thanks Boris. I spent a bit of time and got a VM running with a xen 4.9 hypervisor and a kernel with this patch series. It a ubuntu bionic VM with the distro's xen stuff. Can you give some guidance how you made it crash? I see the VM autoloaded gntdev: Module Size Used by xen_gntdev 24576 2 xen_evtchn 16384 1 xenfs 16384 1 xen_privcmd 24576 16 xenfs And lsof says several xen processes have the chardev open: xenstored 819 root 13u CHR 10,53 0t0 19595 /dev/xen/gntdev xenconsol 857 root 8u CHR 10,53 0t0 19595 /dev/xen/gntdev xenconsol 857 860 root 8u CHR 10,53 0t0 19595 /dev/xen/gntdev But no crashing.. However, I wasn't able to get my usual debug kernel .config to boot with the xen hypervisor, it crashes on early boot with: (XEN) Dom0 has maximum 8 VCPUs (XEN) Scrubbing Free RAM on 1 nodes using 8 CPUs (XEN) .done. (XEN) Initial low memory virq threshold set at 0x1000 pages. (XEN) Std. Loglevel: All (XEN) Guest Loglevel: All (XEN) *** Serial input -> DOM0 (type 'CTRL-a' three times to switch input to Xen) (XEN) Freed 468kB init memory (XEN) d0v0 Unhandled page fault fault/trap [#14, ec=0002] (XEN) Pagetable walk from fffffbfff0480fbe: (XEN) L4[0x1f7] = 0000000000000000 ffffffffffffffff (XEN) domain_crash_sync called from entry.S: fault at ffff82d080348a06 entry.o#create_bounce_frame+0x135/0x15f (XEN) Domain 0 (vcpu#0) crashed on cpu#0: (XEN) ----[ Xen-4.9.2 x86_64 debug=n Not tainted ]---- (XEN) CPU: 0 (XEN) RIP: e033:[<ffffffff82b9f731>] (XEN) RFLAGS: 0000000000000296 EM: 1 CONTEXT: pv guest (d0v0) (XEN) rax: fffffbfff0480fbe rbx: 0000000000000000 rcx: 00000000c0000101 (XEN) rdx: 00000000ffffffff rsi: ffffffff84026000 rdi: ffffffff82cb4a20 (XEN) rbp: ffffffff82407ff8 rsp: ffffffff82407da0 r8: 0000000000000000 (XEN) r9: 0000000000000000 r10: 0000000000000000 r11: 0000000000000000 (XEN) r12: 0000000000000000 r13: 1ffffffff0480fbe r14: 0000000000000000 (XEN) r15: 0000000000000000 cr0: 000000008005003b cr4: 00000000003506e0 (XEN) cr3: 0000000034027000 cr2: fffffbfff0480fbe (XEN) fsb: 0000000000000000 gsb: ffffffff82b61000 gss: 0000000000000000 (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e02b cs: e033 Which is surely some .config issue, but I didn't figure out what. Jason
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