Re: [Intel-gfx] [RFC v3 3/3] drm/doc/rfc: VM_BIND uapi definition

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On Thu, Jun 09, 2022 at 09:36:48AM +0100, Matthew Auld wrote:
On 08/06/2022 22:32, Niranjana Vishwanathapura wrote:
On Wed, Jun 08, 2022 at 10:12:05AM +0100, Matthew Auld wrote:
On 08/06/2022 08:17, Tvrtko Ursulin wrote:

On 07/06/2022 20:37, Niranjana Vishwanathapura wrote:
On Tue, Jun 07, 2022 at 11:27:14AM +0100, Tvrtko Ursulin wrote:

On 17/05/2022 19:32, Niranjana Vishwanathapura wrote:
VM_BIND and related uapi definitions

v2: Ensure proper kernel-doc formatting with cross references.
    Also add new uapi and documentation as per review comments
    from Daniel.

Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx>
---
 Documentation/gpu/rfc/i915_vm_bind.h | 399 +++++++++++++++++++++++++++
 1 file changed, 399 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..589c0a009107
--- /dev/null
+++ b/Documentation/gpu/rfc/i915_vm_bind.h
@@ -0,0 +1,399 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2022 Intel Corporation
+ */
+
+/**
+ * DOC: I915_PARAM_HAS_VM_BIND
+ *
+ * VM_BIND feature availability.
+ * See typedef drm_i915_getparam_t param.
+ */
+#define I915_PARAM_HAS_VM_BIND        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.
+ *
+ * A VM in VM_BIND mode will not support the older execbuff mode of binding. + * In VM_BIND mode, execbuff ioctl will not accept any execlist (ie., the
+ * &drm_i915_gem_execbuffer2.buffer_count must be 0).
+ * Also, &drm_i915_gem_execbuffer2.batch_start_offset and
+ * &drm_i915_gem_execbuffer2.batch_len must be 0.
+ * DRM_I915_GEM_EXECBUFFER_EXT_BATCH_ADDRESSES extension must be provided
+ * to pass in the batch buffer addresses.
+ *
+ * Additionally, I915_EXEC_NO_RELOC, I915_EXEC_HANDLE_LUT and
+ * I915_EXEC_BATCH_FIRST of &drm_i915_gem_execbuffer2.flags must be 0 + * (not used) in VM_BIND mode. I915_EXEC_USE_EXTENSIONS flag must always be
+ * set (See struct drm_i915_gem_execbuffer_ext_batch_addresses).
+ * The buffers_ptr, buffer_count, batch_start_offset and batch_len fields + * of struct drm_i915_gem_execbuffer2 are also not used and must be 0.
+ */
+#define I915_VM_CREATE_FLAGS_USE_VM_BIND    (1 << 0)
+
+/**
+ * DOC: I915_CONTEXT_CREATE_FLAGS_LONG_RUNNING
+ *
+ * Flag to declare context as long running.
+ * See struct drm_i915_gem_context_create_ext flags.
+ *
+ * Usage of dma-fence expects that they complete in reasonable amount of time. + * Compute on the other hand can be long running. Hence it is not appropriate + * for compute contexts to export request completion dma-fence to user. + * The dma-fence usage will be limited to in-kernel consumption only.
+ * Compute contexts need to use user/memory fence.
+ *
+ * So, long running contexts do not support output fences. Hence,
+ * I915_EXEC_FENCE_OUT (See &drm_i915_gem_execbuffer2.flags and
+ * I915_EXEC_FENCE_SIGNAL (See &drm_i915_gem_exec_fence.flags) are expected
+ * to be not used.
+ *
+ * DRM_I915_GEM_WAIT ioctl call is also not supported for objects mapped
+ * to long running contexts.
+ */
+#define I915_CONTEXT_CREATE_FLAGS_LONG_RUNNING   (1u << 2)
+
+/* VM_BIND related ioctls */
+#define DRM_I915_GEM_VM_BIND        0x3d
+#define DRM_I915_GEM_VM_UNBIND        0x3e
+#define DRM_I915_GEM_WAIT_USER_FENCE    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_WAIT_USER_FENCE DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_WAIT_USER_FENCE, struct drm_i915_gem_wait_user_fence)
+
+/**
+ * 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).
+ */
+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;

Does it support, or should it, equivalent of EXEC_OBJECT_PAD_TO_SIZE? Or if not userspace is expected to map the remainder of the space to a dummy object? In which case would there be any alignment/padding issues preventing the two bind to be placed next to each other?

I ask because someone from the compute side asked me about a problem with their strategy of dealing with overfetch and I suggested pad to size.


Thanks Tvrtko,
I think we shouldn't be needing it. As with VM_BIND VA assignment
is completely pushed to userspace, no padding should be necessary
once the 'start' and 'size' alignment conditions are met.

I will add some documentation on alignment requirement here.
Generally, 'start' and 'size' should be 4K aligned. But, I think
when we have 64K lmem page sizes (dg2 and xehpsdv), they need to
be 64K aligned.

+ Matt

Align to 64k is enough for all overfetch issues?

Apparently compute has a situation where a buffer is received by one component and another has to apply more alignment to it, to deal with overfetch. Since they cannot grow the actual BO if they wanted to VM_BIND a scratch area on top? Or perhaps none of this is a problem on discrete and original BO should be correctly allocated to start with.

Side question - what about the align to 2MiB mentioned in i915_vma_insert to avoid mixing 4k and 64k PTEs? That does not apply to discrete?

Not sure about the overfetch thing, but yeah dg2 & xehpsdv both require a minimum of 64K pages underneath for local memory, and the BO size will also be rounded up accordingly. And yeah the complication arises due to not being able to mix 4K + 64K GTT pages within the same page-table (existed since even gen8). Note that 4K here is what we typically get for system memory.

Originally we had a memory coloring scheme to track the "color" of each page-table, which basically ensures that userspace can't do something nasty like mixing page sizes. The advantage of that scheme is that we would only require 64K GTT alignment and no extra padding, but is perhaps a little complex.

The merged solution is just to align and pad (i.e vma->node.size and not vma->size) out of the vma to 2M, which is dead simple implementation wise, but does potentially waste some GTT space and some of the local memory used for the actual page-table. For the alignment the kernel just validates that the GTT address is aligned to 2M in vma_insert(), and then for the padding it just inflates it to 2M, if userspace hasn't already.

See the kernel-doc for @size: https://dri.freedesktop.org/docs/drm/gpu/driver-uapi.html?#c.drm_i915_gem_create_ext



Ok, those requirements (2M VA alignment) will apply to VM_BIND also.
This is unfortunate, but it is not something new enforced by VM_BIND.
Other option is to go with 64K alignment and in VM_BIND case, user
must ensure there is no mix-matching of 64K (lmem) and 4k (smem)
mappings in the same 2M range. But this is not VM_BIND specific
(will apply to soft-pinning in execbuf2 also).

I don't think we need any VA padding here as with VM_BIND VA is
managed fully by the user. If we enforce VA to be 2M aligned, it
will leave holes (if BOs are smaller then 2M), but nobody is going
to allocate anything form there.

Note that we only apply the 2M alignment + padding for local memory pages, for system memory we don't have/need such restrictions. The VA padding then importantly prevents userspace from incorrectly (or maliciously) inserting 4K system memory object in some page-table operating in 64K GTT mode.


Thanks Matt.
I also, syned offline with Matt a bit on this.
We don't need explicit 'pad_to_size' size. i915 driver is implicitly
padding the size to 2M boundary for LMEM BOs which will apply for
VM_BIND also.
The remaining question is whether we enforce 2M VA alignment for
lmem BOs (just like legacy execbuff path) on dg2 & xehpsdv, or go with
just 64K alignment but ensure there is no mixing of 4K and 64K
mappings in same 2M range. I think we can go with 2M alignment
requirement for VM_BIND also. So, no new requirements here for VM_BIND.

I will update the documentation.

Niranjana


Niranjana


Regards,

Tvrtko


Niranjana

Regards,

Tvrtko

+
+    /**
+     * @flags: Supported flags are,
+     *
+     * I915_GEM_VM_BIND_READONLY:
+     * Mapping is read-only.
+     *
+     * I915_GEM_VM_BIND_CAPTURE:
+     * Capture this mapping in the dump upon GPU error.
+     */
+    __u64 flags;
+#define I915_GEM_VM_BIND_READONLY    (1 << 0)
+#define I915_GEM_VM_BIND_CAPTURE     (1 << 1)
+
+    /** @extensions: 0-terminated chain of extensions for this mapping. */
+    __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). The specified VA range must match one of the + * mappings created with the VM_BIND ioctl. TLB is flushed upon unbind
+ * completion.
+ */
+struct drm_i915_gem_vm_unbind {
+    /** @vm_id: VM (address space) id to bind */
+    __u32 vm_id;
+
+    /** @rsvd: Reserved for future use; must be zero. */
+    __u32 rsvd;
+
+    /** @start: Virtual Address start to unbind */
+    __u64 start;
+
+    /** @length: Length of mapping to unbind */
+    __u64 length;
+
+    /** @flags: reserved for future usage, currently MBZ */
+    __u64 flags;
+
+    /** @extensions: 0-terminated chain of extensions for this mapping. */
+    __u64 extensions;
+};
+
+/**
+ * struct drm_i915_vm_bind_fence - An input or output fence for the vm_bind
+ * or the vm_unbind work.
+ *
+ * The vm_bind or vm_unbind aync worker will wait for input fence to signal
+ * before starting the binding or unbinding.
+ *
+ * The vm_bind or vm_unbind async worker will signal the returned output fence
+ * after the completion of binding or unbinding.
+ */
+struct drm_i915_vm_bind_fence {
+    /** @handle: User's handle for a drm_syncobj to wait on or signal. */
+    __u32 handle;
+
+    /**
+     * @flags: Supported flags are,
+     *
+     * I915_VM_BIND_FENCE_WAIT:
+     * Wait for the input fence before binding/unbinding
+     *
+     * I915_VM_BIND_FENCE_SIGNAL:
+     * Return bind/unbind completion fence as output
+     */
+    __u32 flags;
+#define I915_VM_BIND_FENCE_WAIT            (1<<0)
+#define I915_VM_BIND_FENCE_SIGNAL          (1<<1)
+#define __I915_VM_BIND_FENCE_UNKNOWN_FLAGS (-(I915_VM_BIND_FENCE_SIGNAL << 1))
+};
+
+/**
+ * struct drm_i915_vm_bind_ext_timeline_fences - Timeline fences for vm_bind
+ * and vm_unbind.
+ *
+ * This structure describes an array of timeline drm_syncobj and associated + * points for timeline variants of drm_syncobj. These timeline 'drm_syncobj's + * can be input or output fences (See struct drm_i915_vm_bind_fence).
+ */
+struct drm_i915_vm_bind_ext_timeline_fences {
+#define I915_VM_BIND_EXT_timeline_FENCES    0
+    /** @base: Extension link. See struct i915_user_extension. */
+    struct i915_user_extension base;
+
+    /**
+     * @fence_count: Number of elements in the @handles_ptr & @value_ptr
+     * arrays.
+     */
+    __u64 fence_count;
+
+    /**
+     * @handles_ptr: Pointer to an array of struct drm_i915_vm_bind_fence
+     * of length @fence_count.
+     */
+    __u64 handles_ptr;
+
+    /**
+     * @values_ptr: Pointer to an array of u64 values of length
+     * @fence_count.
+     * Values 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 values_ptr;
+};
+
+/**
+ * struct drm_i915_vm_bind_user_fence - An input or output user fence for the
+ * vm_bind or the vm_unbind work.
+ *
+ * The vm_bind or vm_unbind aync worker will wait for the input fence (value at + * @addr to become equal to @val) before starting the binding or unbinding.
+ *
+ * The vm_bind or vm_unbind async worker will signal the output fence after + * the completion of binding or unbinding by writing @val to memory location at
+ * @addr
+ */
+struct drm_i915_vm_bind_user_fence {
+    /** @addr: User/Memory fence qword aligned process virtual address */
+    __u64 addr;
+
+    /** @val: User/Memory fence value to be written after bind completion */
+    __u64 val;
+
+    /**
+     * @flags: Supported flags are,
+     *
+     * I915_VM_BIND_USER_FENCE_WAIT:
+     * Wait for the input fence before binding/unbinding
+     *
+     * I915_VM_BIND_USER_FENCE_SIGNAL:
+     * Return bind/unbind completion fence as output
+     */
+    __u32 flags;
+#define I915_VM_BIND_USER_FENCE_WAIT            (1<<0)
+#define I915_VM_BIND_USER_FENCE_SIGNAL          (1<<1)
+#define __I915_VM_BIND_USER_FENCE_UNKNOWN_FLAGS \
+    (-(I915_VM_BIND_USER_FENCE_SIGNAL << 1))
+};
+
+/**
+ * struct drm_i915_vm_bind_ext_user_fence - User/memory fences for vm_bind
+ * and vm_unbind.
+ *
+ * These user fences can be input or output fences
+ * (See struct drm_i915_vm_bind_user_fence).
+ */
+struct drm_i915_vm_bind_ext_user_fence {
+#define I915_VM_BIND_EXT_USER_FENCES    1
+    /** @base: Extension link. See struct i915_user_extension. */
+    struct i915_user_extension base;
+
+    /** @fence_count: Number of elements in the @user_fence_ptr array. */
+    __u64 fence_count;
+
+    /**
+     * @user_fence_ptr: Pointer to an array of
+     * struct drm_i915_vm_bind_user_fence of length @fence_count.
+     */
+    __u64 user_fence_ptr;
+};
+
+/**
+ * struct drm_i915_gem_execbuffer_ext_batch_addresses - Array of batch buffer
+ * gpu virtual addresses.
+ *
+ * In the execbuff ioctl (See struct drm_i915_gem_execbuffer2), this extension + * must always be appended in the VM_BIND mode and it will be an error to
+ * append this extension in older non-VM_BIND mode.
+ */
+struct drm_i915_gem_execbuffer_ext_batch_addresses {
+#define DRM_I915_GEM_EXECBUFFER_EXT_BATCH_ADDRESSES    1
+    /** @base: Extension link. See struct i915_user_extension. */
+    struct i915_user_extension base;
+
+    /** @count: Number of addresses in the addr array. */
+    __u32 count;
+
+    /** @addr: An array of batch gpu virtual addresses. */
+    __u64 addr[0];
+};
+
+/**
+ * struct drm_i915_gem_execbuffer_ext_user_fence - First level batch completion
+ * signaling extension.
+ *
+ * This extension allows user to attach a user fence (@addr, @value pair) to an + * execbuf to be signaled by the command streamer after the completion of first + * level batch, by writing the @value at specified @addr and triggering an
+ * interrupt.
+ * User can either poll for this user fence to signal or can also wait on it
+ * with i915_gem_wait_user_fence ioctl.
+ * This is very much usefaul for long running contexts where waiting on dma-fence
+ * by user (like i915_gem_wait ioctl) is not supported.
+ */
+struct drm_i915_gem_execbuffer_ext_user_fence {
+#define DRM_I915_GEM_EXECBUFFER_EXT_USER_FENCE        2
+    /** @base: Extension link. See struct i915_user_extension. */
+    struct i915_user_extension base;
+
+    /**
+     * @addr: User/Memory fence qword aligned GPU virtual address.
+     *
+     * Address has to be a valid GPU virtual address at the time of
+     * first level batch completion.
+     */
+    __u64 addr;
+
+    /**
+     * @value: User/Memory fence Value to be written to above address
+     * after first level batch completes.
+     */
+    __u64 value;
+
+    /** @rsvd: Reserved for future extensions, MBZ */
+    __u64 rsvd;
+};
+
+/**
+ * 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;
+};
+
+/**
+ * struct drm_i915_gem_wait_user_fence - Wait on user/memory fence.
+ *
+ * User/Memory fence can be woken up either by:
+ *
+ * 1. GPU context indicated by @ctx_id, or,
+ * 2. Kerrnel driver async worker upon I915_UFENCE_WAIT_SOFT.
+ *    @ctx_id is ignored when this flag is set.
+ *
+ * Wakeup condition is,
+ * ``((*addr & mask) op (value & mask))``
+ *
+ * See :ref:`Documentation/driver-api/dma-buf.rst <indefinite_dma_fences>`
+ */
+struct drm_i915_gem_wait_user_fence {
+    /** @extensions: Zero-terminated chain of extensions. */
+    __u64 extensions;
+
+    /** @addr: User/Memory fence address */
+    __u64 addr;
+
+    /** @ctx_id: Id of the Context which will signal the fence. */
+    __u32 ctx_id;
+
+    /** @op: Wakeup condition operator */
+    __u16 op;
+#define I915_UFENCE_WAIT_EQ      0
+#define I915_UFENCE_WAIT_NEQ     1
+#define I915_UFENCE_WAIT_GT      2
+#define I915_UFENCE_WAIT_GTE     3
+#define I915_UFENCE_WAIT_LT      4
+#define I915_UFENCE_WAIT_LTE     5
+#define I915_UFENCE_WAIT_BEFORE  6
+#define I915_UFENCE_WAIT_AFTER   7
+
+    /**
+     * @flags: Supported flags are,
+     *
+     * I915_UFENCE_WAIT_SOFT:
+     *
+     * To be woken up by i915 driver async worker (not by GPU).
+     *
+     * I915_UFENCE_WAIT_ABSTIME:
+     *
+     * Wait timeout specified as absolute time.
+     */
+    __u16 flags;
+#define I915_UFENCE_WAIT_SOFT    0x1
+#define I915_UFENCE_WAIT_ABSTIME 0x2
+
+    /** @value: Wakeup value */
+    __u64 value;
+
+    /** @mask: Wakeup mask */
+    __u64 mask;
+#define I915_UFENCE_WAIT_U8     0xffu
+#define I915_UFENCE_WAIT_U16    0xffffu
+#define I915_UFENCE_WAIT_U32    0xfffffffful
+#define I915_UFENCE_WAIT_U64    0xffffffffffffffffull
+
+    /**
+     * @timeout: Wait timeout in nanoseconds.
+     *
+     * If I915_UFENCE_WAIT_ABSTIME flag is set, then time timeout is the
+     * absolute time in nsec.
+     */
+    __s64 timeout;
+};



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