On Tue, Jun 08, 2021 at 11:35:58PM -0500, Jason Ekstrand wrote:
> The current context uAPI allows for two methods of setting context
> parameters: SET_CONTEXT_PARAM and CONTEXT_CREATE_EXT_SETPARAM. The
> former is allowed to be called at any time while the later happens as
> part of GEM_CONTEXT_CREATE. Currently, everything settable via one is
> settable via the other. While some params are fairly simple and setting
> them on a live context is harmless such the context priority, others are
> far trickier such as the VM or the set of engines. In order to swap out
> the VM, for instance, we have to delay until all current in-flight work
> is complete, swap in the new VM, and then continue. This leads to a
> plethora of potential race conditions we'd really rather avoid.
>
> Unfortunately, both methods of setting the VM and the engine set are in
> active use today so we can't simply disallow setting the VM or engine
> set vial SET_CONTEXT_PARAM. In order to work around this wart, this
> commit adds a proto-context struct which contains all the context create
> parameters.
>
> v2 (Daniel Vetter):
> - Better commit message
> - Use __set/clear_bit instead of set/clear_bit because there's no race
> and we don't need the atomics
>
> v3 (Daniel Vetter):
> - Use manual bitops and BIT() instead of __set_bit
>
> v4 (Daniel Vetter):
> - Add a changelog to the commit message
> - Better hyperlinking in docs
> - Create the default PPGTT in i915_gem_create_context
>
> Signed-off-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_context.c | 124 +++++++++++++++---
> .../gpu/drm/i915/gem/i915_gem_context_types.h | 22 ++++
> .../gpu/drm/i915/gem/selftests/mock_context.c | 16 ++-
> 3 files changed, 145 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index f9a6eac78c0ae..b5d8c1ff5d7b3 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -191,6 +191,83 @@ static int validate_priority(struct drm_i915_private *i915,
> return 0;
> }
>
> +static void proto_context_close(struct i915_gem_proto_context *pc)
> +{
> + if (pc->vm)
> + i915_vm_put(pc->vm);
> + kfree(pc);
> +}
> +
> +static int proto_context_set_persistence(struct drm_i915_private *i915,
> + struct i915_gem_proto_context *pc,
> + bool persist)
> +{
> + if (persist) {
> + /*
> + * Only contexts that are short-lived [that will expire or be
> + * reset] are allowed to survive past termination. We require
> + * hangcheck to ensure that the persistent requests are healthy.
> + */
> + if (!i915->params.enable_hangcheck)
> + return -EINVAL;
> +
> + pc->user_flags |= BIT(UCONTEXT_PERSISTENCE);
> + } else {
> + /* To cancel a context we use "preempt-to-idle" */
> + if (!(i915->caps.scheduler & I915_SCHEDULER_CAP_PREEMPTION))
> + return -ENODEV;
> +
> + /*
> + * If the cancel fails, we then need to reset, cleanly!
> + *
> + * If the per-engine reset fails, all hope is lost! We resort
> + * to a full GPU reset in that unlikely case, but realistically
> + * if the engine could not reset, the full reset does not fare
> + * much better. The damage has been done.
> + *
> + * However, if we cannot reset an engine by itself, we cannot
> + * cleanup a hanging persistent context without causing
> + * colateral damage, and we should not pretend we can by
> + * exposing the interface.
> + */
> + if (!intel_has_reset_engine(&i915->gt))
> + return -ENODEV;
> +
> + pc->user_flags &= ~BIT(UCONTEXT_PERSISTENCE);
> + }
> +
> + return 0;
> +}
> +
> +static struct i915_gem_proto_context *
> +proto_context_create(struct drm_i915_private *i915, unsigned int flags)
> +{
> + struct i915_gem_proto_context *pc, *err;
> +
> + pc = kzalloc(sizeof(*pc), GFP_KERNEL);
> + if (!pc)
> + return ERR_PTR(-ENOMEM);
> +
> + pc->user_flags = BIT(UCONTEXT_BANNABLE) |
> + BIT(UCONTEXT_RECOVERABLE);
> + proto_context_set_persistence(i915, pc, true);
I think we're down to the bikeshed here that I think should be open-coded
for clarity of what exactly is going on. But maybe better in a distinct
patch.
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> + pc->sched.priority = I915_PRIORITY_NORMAL;
> +
> + if (flags & I915_CONTEXT_CREATE_FLAGS_SINGLE_TIMELINE) {
> + if (!HAS_EXECLISTS(i915)) {
> + err = ERR_PTR(-EINVAL);
> + goto proto_close;
> + }
> + pc->single_timeline = true;
> + }
> +
> + return pc;
> +
> +proto_close:
> + proto_context_close(pc);
> + return err;
> +}
> +
> static struct i915_address_space *
> context_get_vm_rcu(struct i915_gem_context *ctx)
> {
> @@ -660,7 +737,8 @@ static int __context_set_persistence(struct i915_gem_context *ctx, bool state)
> }
>
> static struct i915_gem_context *
> -__create_context(struct drm_i915_private *i915)
> +__create_context(struct drm_i915_private *i915,
> + const struct i915_gem_proto_context *pc)
> {
> struct i915_gem_context *ctx;
> struct i915_gem_engines *e;
> @@ -673,7 +751,7 @@ __create_context(struct drm_i915_private *i915)
>
> kref_init(&ctx->ref);
> ctx->i915 = i915;
> - ctx->sched.priority = I915_PRIORITY_NORMAL;
> + ctx->sched = pc->sched;
> mutex_init(&ctx->mutex);
> INIT_LIST_HEAD(&ctx->link);
>
> @@ -696,9 +774,7 @@ __create_context(struct drm_i915_private *i915)
> * is no remap info, it will be a NOP. */
> ctx->remap_slice = ALL_L3_SLICES(i915);
>
> - i915_gem_context_set_bannable(ctx);
> - i915_gem_context_set_recoverable(ctx);
> - __context_set_persistence(ctx, true /* cgroup hook? */);
> + ctx->user_flags = pc->user_flags;
>
> for (i = 0; i < ARRAY_SIZE(ctx->hang_timestamp); i++)
> ctx->hang_timestamp[i] = jiffies - CONTEXT_FAST_HANG_JIFFIES;
> @@ -786,20 +862,22 @@ static void __assign_ppgtt(struct i915_gem_context *ctx,
> }
>
> static struct i915_gem_context *
> -i915_gem_create_context(struct drm_i915_private *i915, unsigned int flags)
> +i915_gem_create_context(struct drm_i915_private *i915,
> + const struct i915_gem_proto_context *pc)
> {
> struct i915_gem_context *ctx;
> int ret;
>
> - if (flags & I915_CONTEXT_CREATE_FLAGS_SINGLE_TIMELINE &&
> - !HAS_EXECLISTS(i915))
> - return ERR_PTR(-EINVAL);
> -
> - ctx = __create_context(i915);
> + ctx = __create_context(i915, pc);
> if (IS_ERR(ctx))
> return ctx;
>
> - if (HAS_FULL_PPGTT(i915)) {
> + if (pc->vm) {
> + /* __assign_ppgtt() requires this mutex to be held */
> + mutex_lock(&ctx->mutex);
> + __assign_ppgtt(ctx, pc->vm);
> + mutex_unlock(&ctx->mutex);
> + } else if (HAS_FULL_PPGTT(i915)) {
> struct i915_ppgtt *ppgtt;
>
> ppgtt = i915_ppgtt_create(&i915->gt);
> @@ -810,14 +888,16 @@ i915_gem_create_context(struct drm_i915_private *i915, unsigned int flags)
> return ERR_CAST(ppgtt);
> }
>
> + /* __assign_ppgtt() requires this mutex to be held */
> mutex_lock(&ctx->mutex);
> __assign_ppgtt(ctx, &ppgtt->vm);
> mutex_unlock(&ctx->mutex);
>
> + /* __assign_ppgtt() takes another reference for us */
> i915_vm_put(&ppgtt->vm);
> }
>
> - if (flags & I915_CONTEXT_CREATE_FLAGS_SINGLE_TIMELINE) {
> + if (pc->single_timeline) {
> ret = drm_syncobj_create(&ctx->syncobj,
> DRM_SYNCOBJ_CREATE_SIGNALED,
> NULL);
> @@ -883,6 +963,7 @@ int i915_gem_context_open(struct drm_i915_private *i915,
> struct drm_file *file)
> {
> struct drm_i915_file_private *file_priv = file->driver_priv;
> + struct i915_gem_proto_context *pc;
> struct i915_gem_context *ctx;
> int err;
> u32 id;
> @@ -892,7 +973,14 @@ int i915_gem_context_open(struct drm_i915_private *i915,
> /* 0 reserved for invalid/unassigned ppgtt */
> xa_init_flags(&file_priv->vm_xa, XA_FLAGS_ALLOC1);
>
> - ctx = i915_gem_create_context(i915, 0);
> + pc = proto_context_create(i915, 0);
> + if (IS_ERR(pc)) {
> + err = PTR_ERR(pc);
> + goto err;
> + }
> +
> + ctx = i915_gem_create_context(i915, pc);
> + proto_context_close(pc);
> if (IS_ERR(ctx)) {
> err = PTR_ERR(ctx);
> goto err;
> @@ -1884,6 +1972,7 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
> {
> struct drm_i915_private *i915 = to_i915(dev);
> struct drm_i915_gem_context_create_ext *args = data;
> + struct i915_gem_proto_context *pc;
> struct create_ext ext_data;
> int ret;
> u32 id;
> @@ -1906,7 +1995,12 @@ int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
> return -EIO;
> }
>
> - ext_data.ctx = i915_gem_create_context(i915, args->flags);
> + pc = proto_context_create(i915, args->flags);
> + if (IS_ERR(pc))
> + return PTR_ERR(pc);
> +
> + ext_data.ctx = i915_gem_create_context(i915, pc);
> + proto_context_close(pc);
> if (IS_ERR(ext_data.ctx))
> return PTR_ERR(ext_data.ctx);
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> index 5f0673a2129f9..e0bdf3e298a6a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
> @@ -66,6 +66,28 @@ struct i915_gem_engines_iter {
> const struct i915_gem_engines *engines;
> };
>
> +/**
> + * struct i915_gem_proto_context - prototype context
> + *
> + * The struct i915_gem_proto_context represents the creation parameters for
> + * a struct i915_gem_context. This is used to gather parameters provided
> + * either through creation flags or via SET_CONTEXT_PARAM so that, when we
> + * create the final i915_gem_context, those parameters can be immutable.
> + */
> +struct i915_gem_proto_context {
> + /** @vm: See &i915_gem_context.vm */
> + struct i915_address_space *vm;
> +
> + /** @user_flags: See &i915_gem_context.user_flags */
> + unsigned long user_flags;
> +
> + /** @sched: See &i915_gem_context.sched */
> + struct i915_sched_attr sched;
> +
> + /** @single_timeline: See See &i915_gem_context.syncobj */
> + bool single_timeline;
> +};
> +
> /**
> * struct i915_gem_context - client state
> *
> diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_context.c b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> index 51b5a3421b400..e0f512ef7f3c6 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/mock_context.c
> @@ -80,11 +80,17 @@ void mock_init_contexts(struct drm_i915_private *i915)
> struct i915_gem_context *
> live_context(struct drm_i915_private *i915, struct file *file)
> {
> + struct i915_gem_proto_context *pc;
> struct i915_gem_context *ctx;
> int err;
> u32 id;
>
> - ctx = i915_gem_create_context(i915, 0);
> + pc = proto_context_create(i915, 0);
> + if (IS_ERR(pc))
> + return ERR_CAST(pc);
> +
> + ctx = i915_gem_create_context(i915, pc);
> + proto_context_close(pc);
> if (IS_ERR(ctx))
> return ctx;
>
> @@ -142,8 +148,14 @@ struct i915_gem_context *
> kernel_context(struct drm_i915_private *i915)
> {
> struct i915_gem_context *ctx;
> + struct i915_gem_proto_context *pc;
> +
> + pc = proto_context_create(i915, 0);
> + if (IS_ERR(pc))
> + return ERR_CAST(pc);
>
> - ctx = i915_gem_create_context(i915, 0);
> + ctx = i915_gem_create_context(i915, pc);
> + proto_context_close(pc);
> if (IS_ERR(ctx))
> return ctx;
>
> --
> 2.31.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
