On Tue, Apr 16, 2024 at 10:09:46AM +0200, Janusz Krzysztofik wrote:
> Hi Rodrigo,
>
> On Tuesday, 16 April 2024 03:16:31 CEST Rodrigo Vivi wrote:
> > On Mon, Apr 15, 2024 at 09:53:09PM +0200, Janusz Krzysztofik wrote:
> > > We defer actually closing, unbinding and destroying a VMA until next idle
> > > point, or until the object is freed in the meantime. By postponing the
> > > unbind, we allow for the VMA to be reopened by the client, avoiding the
> > > work required to rebind the VMA.
> > >
> > > It was assumed that as long as a GT is held idle, no VMA would be reopened
> > > while we destroy them. That assumption is no longer true in multi-GT
> > > configurations, where a VMA we reopen may be handled by a GT different
> > > from the one that we already keep active via its engine while we set up
> > > an execbuf request.
> > >
> > > <4> [260.290809] ------------[ cut here ]------------
> > > <4> [260.290988] list_del corruption. prev->next should be ffff888118c5d990, but was ffff888118c5a510. (prev=ffff888118c5a510)
> > > <4> [260.291004] WARNING: CPU: 2 PID: 1143 at lib/list_debug.c:62 __list_del_entry_valid_or_report+0xb7/0xe0
> > > ..
> > > <4> [260.291055] CPU: 2 PID: 1143 Comm: kms_plane Not tainted 6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> > > <4> [260.291058] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> > > <4> [260.291060] RIP: 0010:__list_del_entry_valid_or_report+0xb7/0xe0
> > > ...
> > > <4> [260.291087] Call Trace:
> > > <4> [260.291089] <TASK>
> > > <4> [260.291124] i915_vma_reopen+0x43/0x80 [i915]
> > > <4> [260.291298] eb_lookup_vmas+0x9cb/0xcc0 [i915]
> > > <4> [260.291579] i915_gem_do_execbuffer+0xc9a/0x26d0 [i915]
> > > <4> [260.291883] i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> > > ...
> > > <4> [260.292301] </TASK>
> > > ...
> > > <4> [260.292506] ---[ end trace 0000000000000000 ]---
> > > <4> [260.292782] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6ca3: 0000 [#1] PREEMPT SMP NOPTI
> > > <4> [260.303575] CPU: 2 PID: 1143 Comm: kms_plane Tainted: G W 6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> > > <4> [260.313851] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> > > <4> [260.326359] RIP: 0010:eb_validate_vmas+0x114/0xd80 [i915]
> > > ...
> > > <4> [260.428756] Call Trace:
> > > <4> [260.431192] <TASK>
> > > <4> [639.283393] i915_gem_do_execbuffer+0xd05/0x26d0 [i915]
> > > <4> [639.305245] i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> > > ...
> > > <4> [639.411134] </TASK>
> > > ...
> > > <4> [639.449979] ---[ end trace 0000000000000000 ]---
> > >
> > > As soon as we start unbinding and destroying a VMA, marked it as parked,
> > > and also keep it marked as closed for the rest of its life. When a VMA
> > > to be opened occurs closed, reopen it only if not yet parked.
> > >
> > > v3: Fix misplaced brackets.
> > > v2: Since we no longer re-init the VMA closed list link on VMA park so it
> > > looks like still on a list, don't try to delete it from the list again
> > > after the VMA has been marked as parked.
> > >
> > > Fixes: b0647a5e79b1 ("drm/i915: Avoid live-lock with i915_vma_parked()")
> >
> > what about reverting that?
>
> I didn't think of that. Why you think that might be a better approach?
well, I thought of that mainly because...
>
> Anyway, that's a 4 years old patch and a few things have changed since then,
> so simple revert won't work. Moreover, I've just checked that patch was
> supposed to fix another patch, 77853186e547 ("drm/i915: Claim vma while under
> closed_lock in i915_vma_parked()"), which in turn was supposed to fix
> aa5e4453dc05 ("drm/i915/gem: Try to flush pending unbind events"), and that
> one also referenced still another, cb6c3d45f948 ("drm/i915/gem: Avoid parking
> the vma as we unbind") from December 2019, which finally wasn't a fix but an
> improvement.
... because of histories like that ^ and I was afraid of this patch here now
just put us into a different corner case.
I have a feeling that without locks there we might just hit another
race soon with the the park and only using the atomic checks.
> Then, we would have to consider new fixes alternative to at least
> some of those three, I guess.
Indeed.. I didn't think that deep on that...
> I'd rather not dig that deep, unless we invest
> in a completely new solution (e.g. backport VMA handling from xe if more
> effective while compatible to some extent?). Even then, we need a fix for
> now.
yeap, not sure if that would help. was also not designed to
the park unpark.
>
> Alternatively, we can try to revert my 1f33dc0c1189 ("drm/i915: Remove extra
> multi-gt pm-references") which was a manual revert of f56fe3e91787 ("drm/i915:
> Fix a VMA UAF for multi-gt platform") -- a workaround that was supposed to
> address some multi-GT related VMA issues. While it didn't really resolve
> those issues it was addressing, I think it may help with this one, which
> started appearing after I reverted that workaround. However, its
> effectiveness is limited to MTL topology.
perhaps the safer path for this case indeed. something that could be really
limited to a single platform would be better.
But I confess that I don't have other better suggestions.
If we need to go with this patch as a quick solution, it is apparently
better than leaving the bug there as is.
+Thomas. any good thoughts there or advices?
Thanks,
Rodrigo.
>
> Thanks,
> Janusz
>
> >
> > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10608
> > > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
> > > Cc: Chris Wilson <chris.p.wilson@xxxxxxxxxxxxxxx>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx # v6.0+
> > > ---
> > > .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 ++++--
> > > drivers/gpu/drm/i915/i915_vma.c | 32 +++++++++++++++----
> > > drivers/gpu/drm/i915/i915_vma.h | 2 +-
> > > drivers/gpu/drm/i915/i915_vma_types.h | 3 ++
> > > 4 files changed, 37 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > index 42619fc05de48..97e014f94002e 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > > @@ -847,9 +847,12 @@ static int __eb_add_lut(struct i915_execbuffer *eb,
> > > if (unlikely(!lut))
> > > return -ENOMEM;
> > >
> > > + if (!i915_vma_open(vma)) {
> > > + err = -EEXIST; /* let eb_vma_lookup() retry */
> > > + goto err_lut_free;
> > > + }
> > > +
> > > i915_vma_get(vma);
> > > - if (!atomic_fetch_inc(&vma->open_count))
> > > - i915_vma_reopen(vma);
> > > lut->handle = handle;
> > > lut->ctx = ctx;
> > >
> > > @@ -880,8 +883,9 @@ static int __eb_add_lut(struct i915_execbuffer *eb,
> > > return 0;
> > >
> > > err:
> > > - i915_vma_close(vma);
> > > i915_vma_put(vma);
> > > + i915_vma_close(vma);
> > > +err_lut_free:
> > > i915_lut_handle_free(lut);
> > > return err;
> > > }
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> > > index d2f064d2525cc..4435c76f28c8c 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.c
> > > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > > @@ -1735,14 +1735,33 @@ static void __i915_vma_remove_closed(struct i915_vma *vma)
> > > list_del_init(&vma->closed_link);
> > > }
> > >
> > > -void i915_vma_reopen(struct i915_vma *vma)
> > > +static struct i915_vma *i915_vma_reopen(struct i915_vma *vma)
> > > +{
> > > + if (atomic_read(&vma->flags) & I915_VMA_PARKED)
> > > + return NULL;
> > > +
> > > + __i915_vma_remove_closed(vma);
> > > + return vma;
> > > +}
> > > +
> > > +struct i915_vma *i915_vma_open(struct i915_vma *vma)
> > > {
> > > struct intel_gt *gt = vma->vm->gt;
> > >
> > > + if (atomic_inc_not_zero(&vma->open_count))
> > > + return vma;
> > > +
> > > spin_lock_irq(>->closed_lock);
> > > - if (i915_vma_is_closed(vma))
> > > - __i915_vma_remove_closed(vma);
> > > + if (!atomic_inc_not_zero(&vma->open_count)) {
> > > + if (i915_vma_is_closed(vma))
> > > + vma = i915_vma_reopen(vma);
> > > +
> > > + if (vma)
> > > + atomic_inc(&vma->open_count);
> > > + }
> > > spin_unlock_irq(>->closed_lock);
> > > +
> > > + return vma;
> > > }
> > >
> > > static void force_unbind(struct i915_vma *vma)
> > > @@ -1770,7 +1789,8 @@ static void release_references(struct i915_vma *vma, struct intel_gt *gt,
> > > spin_unlock(&obj->vma.lock);
> > >
> > > spin_lock_irq(>->closed_lock);
> > > - __i915_vma_remove_closed(vma);
> > > + if (!(atomic_read(&vma->flags) & I915_VMA_PARKED))
> > > + __i915_vma_remove_closed(vma);
> > > spin_unlock_irq(>->closed_lock);
> > >
> > > if (vm_ddestroy)
> > > @@ -1854,22 +1874,22 @@ void i915_vma_parked(struct intel_gt *gt)
> > > }
> > >
> > > list_move(&vma->closed_link, &closed);
> > > + atomic_or(I915_VMA_PARKED, &vma->flags);
> > > }
> > > spin_unlock_irq(>->closed_lock);
> > >
> > > - /* As the GT is held idle, no vma can be reopened as we destroy them */
> > > list_for_each_entry_safe(vma, next, &closed, closed_link) {
> > > struct drm_i915_gem_object *obj = vma->obj;
> > > struct i915_address_space *vm = vma->vm;
> > >
> > > if (i915_gem_object_trylock(obj, NULL)) {
> > > - INIT_LIST_HEAD(&vma->closed_link);
> > > i915_vma_destroy(vma);
> > > i915_gem_object_unlock(obj);
> > > } else {
> > > /* back you go.. */
> > > spin_lock_irq(>->closed_lock);
> > > list_add(&vma->closed_link, >->closed_vma);
> > > + atomic_andnot(I915_VMA_PARKED, &vma->flags);
> > > spin_unlock_irq(>->closed_lock);
> > > }
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
> > > index e356dfb883d34..331d19672c764 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.h
> > > +++ b/drivers/gpu/drm/i915/i915_vma.h
> > > @@ -268,7 +268,7 @@ int __must_check i915_vma_unbind_async(struct i915_vma *vma, bool trylock_vm);
> > > int __must_check i915_vma_unbind_unlocked(struct i915_vma *vma);
> > > void i915_vma_unlink_ctx(struct i915_vma *vma);
> > > void i915_vma_close(struct i915_vma *vma);
> > > -void i915_vma_reopen(struct i915_vma *vma);
> > > +struct i915_vma *i915_vma_open(struct i915_vma *vma);
> > >
> > > void i915_vma_destroy_locked(struct i915_vma *vma);
> > > void i915_vma_destroy(struct i915_vma *vma);
> > > diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
> > > index 559de74d0b114..41784c3025349 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma_types.h
> > > +++ b/drivers/gpu/drm/i915/i915_vma_types.h
> > > @@ -263,6 +263,9 @@ struct i915_vma {
> > > #define I915_VMA_SCANOUT_BIT 17
> > > #define I915_VMA_SCANOUT ((int)BIT(I915_VMA_SCANOUT_BIT))
> > >
> > > +#define I915_VMA_PARKED_BIT 18
> > > +#define I915_VMA_PARKED ((int)BIT(I915_VMA_PARKED_BIT))
> > > +
> > > struct i915_active active;
> > >
> > > #define I915_VMA_PAGES_BIAS 24
> >
>
>
>
>
