On Thu, 2024-04-25 at 20:42 +0200, Janusz Krzysztofik wrote:
> Hi Thomas,
>
> On Tuesday, 16 April 2024 18:40:12 CEST Rodrigo Vivi wrote:
> > 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?
>
> I'm waiting for you opinion here. Which option would you prefer,
> this patch
> or revert of 1f33dc0c1189 ("drm/i915: Remove extra multi-gt pm-
> references")?
> Or can you suggest any potentially better solutions?
Hi,
Sorry for the late response. I don't really have anything to add to the
discussion since I don't have the time to again familiarize myself with
the code.
The only advise I can give is to try to document as much as possible so
that it's reasonably clear what's being done and why.
Thanks,
Thomas
>
> Thanks,
> Janusz
>
> >
> > 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
> > > >
> > >
> > >
> > >
> > >
> >
>
>
>
>
