Re: [PATCH 2/2] drm/msm: Add MSM_WAIT_IOVA ioctl

From: Brian Ho
Date: Mon Jan 13 2020 - 17:55:38 EST

On Mon, Jan 13, 2020 at 09:57:43AM -0800, Kristian Kristensen wrote:
> On Mon, Jan 13, 2020 at 8:25 AM Rob Clark <robdclark@xxxxxxxxxxxx> wrote:
>
> > On Mon, Jan 13, 2020 at 7:37 AM Brian Ho <brian@xxxxxxxxx> wrote:
> > >
> > > Implements an ioctl to wait until a value at a given iova is greater
> > > than or equal to a supplied value.
> > >
> > > This will initially be used by turnip (open-source Vulkan driver for
> > > QC in mesa) for occlusion queries where the userspace driver can
> > > block on a query becoming available before continuing via
> > > vkGetQueryPoolResults.
> > >
> > > Signed-off-by: Brian Ho <brian@xxxxxxxxx>
> > > ---
> > > drivers/gpu/drm/msm/msm_drv.c | 63 +++++++++++++++++++++++++++++++++--
> > > include/uapi/drm/msm_drm.h | 13 ++++++++
> > > 2 files changed, 74 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.c
> > b/drivers/gpu/drm/msm/msm_drv.c
> > > index c84f0a8b3f2c..dcc46874a5a2 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > > @@ -36,10 +36,11 @@
> > > * MSM_GEM_INFO ioctl.
> > > * - 1.4.0 - softpin, MSM_RELOC_BO_DUMP, and GEM_INFO support to set/get
> > > * GEM object's debug name
> > > - * - 1.5.0 - Add SUBMITQUERY_QUERY ioctl
> > > + * - 1.5.0 - Add SUBMITQUEUE_QUERY ioctl
> > > + * - 1.6.0 - Add WAIT_IOVA ioctl
> > > */
> > > #define MSM_VERSION_MAJOR 1
> > > -#define MSM_VERSION_MINOR 5
> > > +#define MSM_VERSION_MINOR 6
> > > #define MSM_VERSION_PATCHLEVEL 0
> > >
> > > static const struct drm_mode_config_funcs mode_config_funcs = {
> > > @@ -952,6 +953,63 @@ static int msm_ioctl_submitqueue_close(struct
> > drm_device *dev, void *data,
> > > return msm_submitqueue_remove(file->driver_priv, id);
> > > }
> > >
> > > +static int msm_ioctl_wait_iova(struct drm_device *dev, void *data,
> > > + struct drm_file *file)
> > > +{
> > > + struct msm_drm_private *priv = dev->dev_private;
> > > + struct drm_gem_object *obj;
> > > + struct drm_msm_wait_iova *args = data;
> > > + ktime_t timeout = to_ktime(args->timeout);
> > > + unsigned long remaining_jiffies = timeout_to_jiffies(&timeout);
> > > + struct msm_gpu *gpu = priv->gpu;
> > > + void *base_vaddr;
> > > + uint64_t *vaddr;
> > > + int ret;
> > > +
> > > + if (args->pad)
> > > + return -EINVAL;
> > > +
> > > + if (!gpu)
> > > + return 0;
> >
> > hmm, I'm not sure we should return zero in this case.. maybe -ENODEV?
> >
> > > +
> > > + obj = drm_gem_object_lookup(file, args->handle);
> > > + if (!obj)
> > > + return -ENOENT;
> > > +
> > > + base_vaddr = msm_gem_get_vaddr(obj);
> > > + if (IS_ERR(base_vaddr)) {
> > > + ret = PTR_ERR(base_vaddr);
> > > + goto err_put_gem_object;
> > > + }
> > > + if (args->offset + sizeof(*vaddr) > obj->size) {
> > > + ret = -EINVAL;
> > > + goto err_put_vaddr;
> > > + }
> > > +
> > > + vaddr = base_vaddr + args->offset;
> > > +
> > > + /* Assumes WC mapping */
> > > + ret = wait_event_interruptible_timeout(
> > > + gpu->event, *vaddr >= args->value,
> > remaining_jiffies);
> >
>
> This needs to do the awkward looking
>
> (int64_t)(*data - value) >= 0
>
> to properly handle the wraparound case.
>

I think this comparison will run into issues if we allow for 64-bit
reference values. For example, if value is ULLONG_MAX, and *data
starts at 0 on the first comparison, we'll immediately return.

It's not too much of an issue in fence_completed (msm_fence.c), but
in this ioctl, *data can grow at an arbitrary rate. Are we concerned
about this?

> > +
> > > + if (ret == 0) {
> > > + ret = -ETIMEDOUT;
> > > + goto err_put_vaddr;
> > > + } else if (ret == -ERESTARTSYS) {
> > > + goto err_put_vaddr;
> > > + }
> >
> > maybe:
> >
> > } else {
> > ret = 0;
> > }
> >
> > and then drop the next three lines?
> >
> > > +
> > > + msm_gem_put_vaddr(obj);
> > > + drm_gem_object_put_unlocked(obj);
> > > + return 0;
> > > +
> > > +err_put_vaddr:
> > > + msm_gem_put_vaddr(obj);
> > > +err_put_gem_object:
> > > + drm_gem_object_put_unlocked(obj);
> > > + return ret;
> > > +}
> > > +
> > > static const struct drm_ioctl_desc msm_ioctls[] = {
> > > DRM_IOCTL_DEF_DRV(MSM_GET_PARAM, msm_ioctl_get_param,
> > DRM_RENDER_ALLOW),
> > > DRM_IOCTL_DEF_DRV(MSM_GEM_NEW, msm_ioctl_gem_new,
> > DRM_RENDER_ALLOW),
> > > @@ -964,6 +1022,7 @@ static const struct drm_ioctl_desc msm_ioctls[] = {
> > > DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_NEW,
> > msm_ioctl_submitqueue_new, DRM_RENDER_ALLOW),
> > > DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_CLOSE,
> > msm_ioctl_submitqueue_close, DRM_RENDER_ALLOW),
> > > DRM_IOCTL_DEF_DRV(MSM_SUBMITQUEUE_QUERY,
> > msm_ioctl_submitqueue_query, DRM_RENDER_ALLOW),
> > > + DRM_IOCTL_DEF_DRV(MSM_WAIT_IOVA, msm_ioctl_wait_iova,
> > DRM_RENDER_ALLOW),
> > > };
> > >
> > > static const struct vm_operations_struct vm_ops = {
> > > diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> > > index 0b85ed6a3710..8477f28a4ee1 100644
> > > --- a/include/uapi/drm/msm_drm.h
> > > +++ b/include/uapi/drm/msm_drm.h
> > > @@ -298,6 +298,17 @@ struct drm_msm_submitqueue_query {
> > > __u32 pad;
> > > };
> > >
> > > +/* This ioctl blocks until the u64 value at bo + offset is greater than
> > or
> > > + * equal to the reference value.
> > > + */
> > > +struct drm_msm_wait_iova {
> > > + __u32 handle; /* in, GEM handle */
> > > + __u32 pad;
> > > + struct drm_msm_timespec timeout; /* in */
> > > + __u64 offset; /* offset into bo */
> > > + __u64 value; /* reference value */
> >
> > Maybe we should go ahead and add a __u64 mask;
> >
> > that would let us wait for 32b values as well, and wait for bits in a
> > bitmask
> >
>
> I think we'd be OK to just default to 32 bit values instead, since most of
> the CP commands that this is intended to work with (CP_EVENT_WRITE,
> CP_WAIT_MEM_GTE etc) operate on 32 bit values. We could move 'value' to the
> slot right after 'handle' but then we'd not have any pad/reserved fields.
> Maybe we keep 'value' 64 bit but restrict it to 32 bits, with an option to
> add a 64 bit flag in 'pad' later on?
>

FWIW, the current usage of this in my mesa MR uses a 64 bit value.
There's no super great reason that the available bit is 64 bits and
not 32 bits (I think it made the addressing math a bit simpler), but
I'm fine with whatever you all decide on here.

> >
> > Other than those minor comments, it looks pretty good to me
> >
> > BR,
> > -R
> >
> > > +};
> > > +
> > > #define DRM_MSM_GET_PARAM 0x00
> > > /* placeholder:
> > > #define DRM_MSM_SET_PARAM 0x01
> > > @@ -315,6 +326,7 @@ struct drm_msm_submitqueue_query {
> > > #define DRM_MSM_SUBMITQUEUE_NEW 0x0A
> > > #define DRM_MSM_SUBMITQUEUE_CLOSE 0x0B
> > > #define DRM_MSM_SUBMITQUEUE_QUERY 0x0C
> > > +#define DRM_MSM_WAIT_IOVA 0x0D
> > >
> > > #define DRM_IOCTL_MSM_GET_PARAM DRM_IOWR(DRM_COMMAND_BASE +
> > DRM_MSM_GET_PARAM, struct drm_msm_param)
> > > #define DRM_IOCTL_MSM_GEM_NEW DRM_IOWR(DRM_COMMAND_BASE +
> > DRM_MSM_GEM_NEW, struct drm_msm_gem_new)
> > > @@ -327,6 +339,7 @@ struct drm_msm_submitqueue_query {
> > > #define DRM_IOCTL_MSM_SUBMITQUEUE_NEW DRM_IOWR(DRM_COMMAND_BASE +
> > DRM_MSM_SUBMITQUEUE_NEW, struct drm_msm_submitqueue)
> > > #define DRM_IOCTL_MSM_SUBMITQUEUE_CLOSE DRM_IOW (DRM_COMMAND_BASE +
> > DRM_MSM_SUBMITQUEUE_CLOSE, __u32)
> > > #define DRM_IOCTL_MSM_SUBMITQUEUE_QUERY DRM_IOW (DRM_COMMAND_BASE +
> > DRM_MSM_SUBMITQUEUE_QUERY, struct drm_msm_submitqueue_query)
> > > +#define DRM_IOCTL_MSM_WAIT_IOVA DRM_IOW (DRM_COMMAND_BASE +
> > DRM_MSM_WAIT_IOVA, struct drm_msm_wait_iova)
> > >
> > > #if defined(__cplusplus)
> > > }
> > > --
> > > 2.25.0.rc1.283.g88dfdc4193-goog
> > >
> >