[Intel-gfx] [PATCH v6 3/3] drm/doc/rfc: VM_BIND uapi definition
Zanoni, Paulo R
paulo.r.zanoni at intel.com
Thu Jun 30 06:39:52 UTC 2022
On Wed, 2022-06-29 at 23:08 -0700, Niranjana Vishwanathapura wrote:
> On Wed, Jun 29, 2022 at 05:33:49PM -0700, Zanoni, Paulo R wrote:
> > On Sat, 2022-06-25 at 18:49 -0700, Niranjana Vishwanathapura wrote:
> > > VM_BIND and related uapi definitions
> > >
> > > v2: Reduce the scope to simple Mesa use case.
> > > v3: Expand VM_UNBIND documentation and add
> > > I915_GEM_VM_BIND/UNBIND_FENCE_VALID
> > > and I915_GEM_VM_BIND_TLB_FLUSH flags.
> > > v4: Remove I915_GEM_VM_BIND_TLB_FLUSH flag and add additional
> > > documentation for vm_bind/unbind.
> > > v5: Remove TLB flush requirement on VM_UNBIND.
> > > Add version support to stage implementation.
> > > v6: Define and use drm_i915_gem_timeline_fence structure for
> > > all timeline fences.
> > > v7: Rename I915_PARAM_HAS_VM_BIND to I915_PARAM_VM_BIND_VERSION.
> > > Update documentation on async vm_bind/unbind and versioning.
> > > Remove redundant vm_bind/unbind FENCE_VALID flag, execbuf3
> > > batch_count field and I915_EXEC3_SECURE flag.
> > >
> > > Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
> > > Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > > ---
> > > Documentation/gpu/rfc/i915_vm_bind.h | 280 +++++++++++++++++++++++++++
> > > 1 file changed, 280 insertions(+)
> > > create mode 100644 Documentation/gpu/rfc/i915_vm_bind.h
> > >
> > > diff --git a/Documentation/gpu/rfc/i915_vm_bind.h b/Documentation/gpu/rfc/i915_vm_bind.h
> > > new file mode 100644
> > > index 000000000000..a93e08bceee6
> > > --- /dev/null
> > > +++ b/Documentation/gpu/rfc/i915_vm_bind.h
> > > @@ -0,0 +1,280 @@
> > > +/* SPDX-License-Identifier: MIT */
> > > +/*
> > > + * Copyright © 2022 Intel Corporation
> > > + */
> > > +
> > > +/**
> > > + * DOC: I915_PARAM_VM_BIND_VERSION
> > > + *
> > > + * VM_BIND feature version supported.
> > > + * See typedef drm_i915_getparam_t param.
> > > + *
> > > + * Specifies the VM_BIND feature version supported.
> > > + * The following versions of VM_BIND have been defined:
> > > + *
> > > + * 0: No VM_BIND support.
> > > + *
> > > + * 1: In VM_UNBIND calls, the UMD must specify the exact mappings created
> > > + * previously with VM_BIND, the ioctl will not support unbinding multiple
> > > + * mappings or splitting them. Similarly, VM_BIND calls will not replace
> > > + * any existing mappings.
> > > + *
> > > + * 2: The restrictions on unbinding partial or multiple mappings is
> > > + * lifted, Similarly, binding will replace any mappings in the given range.
> > > + *
> > > + * See struct drm_i915_gem_vm_bind and struct drm_i915_gem_vm_unbind.
> > > + */
> > > +#define I915_PARAM_VM_BIND_VERSION 57
> > > +
> > > +/**
> > > + * DOC: I915_VM_CREATE_FLAGS_USE_VM_BIND
> > > + *
> > > + * Flag to opt-in for VM_BIND mode of binding during VM creation.
> > > + * See struct drm_i915_gem_vm_control flags.
> > > + *
> > > + * The older execbuf2 ioctl will not support VM_BIND mode of operation.
> > > + * For VM_BIND mode, we have new execbuf3 ioctl which will not accept any
> > > + * execlist (See struct drm_i915_gem_execbuffer3 for more details).
> > > + */
> > > +#define I915_VM_CREATE_FLAGS_USE_VM_BIND (1 << 0)
> > > +
> > > +/* VM_BIND related ioctls */
> > > +#define DRM_I915_GEM_VM_BIND 0x3d
> > > +#define DRM_I915_GEM_VM_UNBIND 0x3e
> > > +#define DRM_I915_GEM_EXECBUFFER3 0x3f
> > > +
> > > +#define DRM_IOCTL_I915_GEM_VM_BIND DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_VM_BIND, struct drm_i915_gem_vm_bind)
> > > +#define DRM_IOCTL_I915_GEM_VM_UNBIND DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_VM_UNBIND, struct drm_i915_gem_vm_bind)
> > > +#define DRM_IOCTL_I915_GEM_EXECBUFFER3 DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_EXECBUFFER3, struct drm_i915_gem_execbuffer3)
> > > +
> > > +/**
> > > + * struct drm_i915_gem_timeline_fence - An input or output timeline fence.
> > > + *
> > > + * The operation will wait for input fence to signal.
> > > + *
> > > + * The returned output fence will be signaled after the completion of the
> > > + * operation.
> > > + */
> > > +struct drm_i915_gem_timeline_fence {
> > > + /** @handle: User's handle for a drm_syncobj to wait on or signal. */
> > > + __u32 handle;
> > > +
> > > + /**
> > > + * @flags: Supported flags are:
> > > + *
> > > + * I915_TIMELINE_FENCE_WAIT:
> > > + * Wait for the input fence before the operation.
> > > + *
> > > + * I915_TIMELINE_FENCE_SIGNAL:
> > > + * Return operation completion fence as output.
> > > + */
> > > + __u32 flags;
> > > +#define I915_TIMELINE_FENCE_WAIT (1 << 0)
> > > +#define I915_TIMELINE_FENCE_SIGNAL (1 << 1)
> > > +#define __I915_TIMELINE_FENCE_UNKNOWN_FLAGS (-(I915_TIMELINE_FENCE_SIGNAL << 1))
> > > +
> > > + /**
> > > + * @value: A point in the timeline.
> > > + * Value must be 0 for a binary drm_syncobj. A Value of 0 for a
> > > + * timeline drm_syncobj is invalid as it turns a drm_syncobj into a
> > > + * binary one.
> > > + */
> > > + __u64 value;
> > > +};
> > > +
> > > +/**
> > > + * struct drm_i915_gem_vm_bind - VA to object mapping to bind.
> > > + *
> > > + * This structure is passed to VM_BIND ioctl and specifies the mapping of GPU
> > > + * virtual address (VA) range to the section of an object that should be bound
> > > + * in the device page table of the specified address space (VM).
> > > + * The VA range specified must be unique (ie., not currently bound) and can
> > > + * be mapped to whole object or a section of the object (partial binding).
> > > + * Multiple VA mappings can be created to the same section of the object
> > > + * (aliasing).
> > > + *
> > > + * The @start, @offset and @length must be 4K page aligned. However the DG2
> > > + * and XEHPSDV has 64K page size for device local-memory and has compact page
> > > + * table. On those platforms, for binding device local-memory objects, the
> > > + * @start must be 2M aligned, @offset and @length must be 64K aligned.
> > > + * Also, for such mappings, i915 will reserve the whole 2M range for it so as
> > > + * to not allow multiple mappings in that 2M range (Compact page tables do not
> > > + * allow 64K page and 4K page bindings in the same 2M range).
> > > + *
> > > + * Error code -EINVAL will be returned if @start, @offset and @length are not
> > > + * properly aligned. In version 1 (See I915_PARAM_VM_BIND_VERSION), error code
> > > + * -ENOSPC will be returned if the VA range specified can't be reserved.
> > > + *
> > > + * VM_BIND/UNBIND ioctl calls executed on different CPU threads concurrently
> > > + * are not ordered. Furthermore, parts of the VM_BIND operation can be done
> > > + * asynchronously, if valid @fence is specified.
> >
> > Does that mean that if I don't provide @fence, then this ioctl will be
> > synchronous (i.e., when it returns, the memory will be guaranteed to be
> > bound)? The text is kinda implying that, but from one of your earlier
> > replies to Tvrtko, that doesn't seem to be the case. I guess we could
> > change the text to make this more explicit.
> >
>
> Yes, I thought, if user doesn't specify the out fence, KMD better make
> the ioctl synchronous by waiting until the binding finishes before
> returning. Otherwise, UMD has no way to ensure binding is complete and
> UMD must pass in out fence for VM_BIND calls.
>
> But latest comment form Daniel on other thread might suggest something else.
> Daniel, can you comment?
Whatever we decide, let's make sure it's documented.
>
> > In addition, previously we had the guarantee that an execbuf ioctl
> > would wait for all the pending vm_bind operations to finish before
> > doing anything. Do we still have this guarantee or do we have to make
> > use of the fences now?
> >
>
> No, we don't have that anymore (execbuf is decoupled from VM_BIND).
> Execbuf3 submission will not wait for any previous VM_BIND to finish.
> UMD must pass in VM_BIND out fence as in fence for execbuf3 to ensure
> that.
Got it, thanks.
>
> > > + */
> > > +struct drm_i915_gem_vm_bind {
> > > + /** @vm_id: VM (address space) id to bind */
> > > + __u32 vm_id;
> > > +
> > > + /** @handle: Object handle */
> > > + __u32 handle;
> > > +
> > > + /** @start: Virtual Address start to bind */
> > > + __u64 start;
> > > +
> > > + /** @offset: Offset in object to bind */
> > > + __u64 offset;
> > > +
> > > + /** @length: Length of mapping to bind */
> > > + __u64 length;
> > > +
> > > + /**
> > > + * @flags: Supported flags are:
> > > + *
> > > + * I915_GEM_VM_BIND_READONLY:
> > > + * Mapping is read-only.
> >
> > Can you please explain what happens when we try to write to a range
> > that's bound as read-only?
> >
>
> It will be mapped as read-only in device page table. Hence any
> write access will fail. I would expect a CAT error reported.
What's a CAT error? Does this lead to machine freeze or a GPU hang?
Let's make sure we document this.
>
> I am seeing that currently the page table R/W setting is based
> on whether BO is readonly or not (UMDs can request a userptr
> BO to readonly). We can make this READONLY here as a subset.
> ie., if BO is readonly, the mappings must be readonly. If BO
> is not readonly, then the mapping can be either readonly or
> not.
>
> But if Mesa doesn't have a use for this, then we can remove
> this flag for now.
>
I was considering using it for Vulkan's Sparse
residencyNonResidentStrict, so we map all unbound pages to a read-only
page. But for that to work, the required behavior would have to be:
reads all return zero, writes are ignored without any sort of error.
But maybe our hardware provides other ways to implement this, I haven't
checked yet.
> >
> > > + *
> > > + * I915_GEM_VM_BIND_CAPTURE:
> > > + * Capture this mapping in the dump upon GPU error.
> > > + */
> > > + __u64 flags;
> > > +#define I915_GEM_VM_BIND_READONLY (1 << 1)
> > > +#define I915_GEM_VM_BIND_CAPTURE (1 << 2)
> > > +
> > > + /**
> > > + * @fence: Timeline fence for bind completion signaling.
> > > + *
> > > + * It is an out fence, hence using I915_TIMELINE_FENCE_WAIT flag
> > > + * is invalid, and an error will be returned.
> > > + */
> > > + struct drm_i915_gem_timeline_fence fence;
> > > +
> > > + /**
> > > + * @extensions: Zero-terminated chain of extensions.
> > > + *
> > > + * For future extensions. See struct i915_user_extension.
> > > + */
> > > + __u64 extensions;
> > > +};
> > > +
> > > +/**
> > > + * struct drm_i915_gem_vm_unbind - VA to object mapping to unbind.
> > > + *
> > > + * This structure is passed to VM_UNBIND ioctl and specifies the GPU virtual
> > > + * address (VA) range that should be unbound from the device page table of the
> > > + * specified address space (VM). VM_UNBIND will force unbind the specified
> > > + * range from device page table without waiting for any GPU job to complete.
> > > + * It is UMDs responsibility to ensure the mapping is no longer in use before
> > > + * calling VM_UNBIND.
> > > + *
> > > + * If the specified mapping is not found, the ioctl will simply return without
> > > + * any error.
> > > + *
> > > + * VM_BIND/UNBIND ioctl calls executed on different CPU threads concurrently
> > > + * are not ordered. Furthermore, parts of the VM_UNBIND operation can be done
> > > + * asynchronously, if valid @fence is specified.
> > > + */
> > > +struct drm_i915_gem_vm_unbind {
> > > + /** @vm_id: VM (address space) id to bind */
> > > + __u32 vm_id;
> > > +
> > > + /** @rsvd: Reserved, MBZ */
> > > + __u32 rsvd;
> > > +
> > > + /** @start: Virtual Address start to unbind */
> > > + __u64 start;
> > > +
> > > + /** @length: Length of mapping to unbind */
> > > + __u64 length;
> > > +
> > > + /** @flags: Currently reserved, MBZ */
> > > + __u64 flags;
> > > +
> > > + /**
> > > + * @fence: Timeline fence for unbind completion signaling.
> > > + *
> > > + * It is an out fence, hence using I915_TIMELINE_FENCE_WAIT flag
> > > + * is invalid, and an error will be returned.
> > > + */
> > > + struct drm_i915_gem_timeline_fence fence;
> > > +
> > > + /**
> > > + * @extensions: Zero-terminated chain of extensions.
> > > + *
> > > + * For future extensions. See struct i915_user_extension.
> > > + */
> > > + __u64 extensions;
> > > +};
> > > +
> > > +/**
> > > + * struct drm_i915_gem_execbuffer3 - Structure for DRM_I915_GEM_EXECBUFFER3
> > > + * ioctl.
> > > + *
> > > + * DRM_I915_GEM_EXECBUFFER3 ioctl only works in VM_BIND mode and VM_BIND mode
> > > + * only works with this ioctl for submission.
> > > + * See I915_VM_CREATE_FLAGS_USE_VM_BIND.
> > > + */
> > > +struct drm_i915_gem_execbuffer3 {
> > > + /**
> > > + * @ctx_id: Context id
> > > + *
> > > + * Only contexts with user engine map are allowed.
> > > + */
> > > + __u32 ctx_id;
> > > +
> > > + /**
> > > + * @engine_idx: Engine index
> > > + *
> > > + * An index in the user engine map of the context specified by @ctx_id.
> > > + */
> > > + __u32 engine_idx;
> > > +
> > > + /**
> > > + * @batch_address: Batch gpu virtual address/es.
> > > + *
> > > + * For normal submission, it is the gpu virtual address of the batch
> > > + * buffer. For parallel submission, it is a pointer to an array of
> > > + * batch buffer gpu virtual addresses with array size equal to the
> > > + * number of (parallel) engines involved in that submission (See
> > > + * struct i915_context_engines_parallel_submit).
> > > + */
> > > + __u64 batch_address;
> > > +
> > > + /** @flags: Currently reserved, MBZ */
> > > + __u64 flags;
> > > +
> > > + /** @rsvd1: Reserved, MBZ */
> > > + __u32 rsvd1;
> > > +
> > > + /** @fence_count: Number of fences in @timeline_fences array. */
> > > + __u32 fence_count;
> > > +
> > > + /**
> > > + * @timeline_fences: Pointer to an array of timeline fences.
> > > + *
> > > + * Timeline fences are of format struct drm_i915_gem_timeline_fence.
> > > + */
> > > + __u64 timeline_fences;
> > > +
> > > + /** @rsvd2: Reserved, MBZ */
> > > + __u64 rsvd2;
> > > +
> >
> > Just out of curiosity: if we can extend behavior with @extensions and
> > even @flags, why would we need a rsvd2? Perhaps we could kill rsvd2?
> >
>
> True. I added it just in case some requests came up that would require
> some additional fields. During this review process itself there were
> some requests. Adding directly here should have a slight performance
> edge over adding it as an extension (one less copy_from_user).
>
> But if folks think this is an overkill, I will remove it.
I do not have strong opinions here, I'm just curious.
Thanks,
Paulo
>
> Niranjana
>
> > > + /**
> > > + * @extensions: Zero-terminated chain of extensions.
> > > + *
> > > + * For future extensions. See struct i915_user_extension.
> > > + */
> > > + __u64 extensions;
> > > +};
> > > +
> > > +/**
> > > + * struct drm_i915_gem_create_ext_vm_private - Extension to make the object
> > > + * private to the specified VM.
> > > + *
> > > + * See struct drm_i915_gem_create_ext.
> > > + */
> > > +struct drm_i915_gem_create_ext_vm_private {
> > > +#define I915_GEM_CREATE_EXT_VM_PRIVATE 2
> > > + /** @base: Extension link. See struct i915_user_extension. */
> > > + struct i915_user_extension base;
> > > +
> > > + /** @vm_id: Id of the VM to which the object is private */
> > > + __u32 vm_id;
> > > +};
> >
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