Quoting Umesh Nerlige Ramappa (2020-07-31 15:46:43)
> i915 used to support time based sampling mode which is good for overall
> system monitoring, but is not enough for query mode used to measure a
> single draw call or dispatch. Gen9-Gen11 are using current i915 perf
> implementation for query, but Gen12+ requires a new approach for query
> based on triggered reports within oa buffer.
>
> Triggering reports into the OA buffer is achieved by writing into a
> a trigger register. Optionally an unused counter/register is set with a
> marker value such that a triggered report can be identified in the OA
> buffer. Reports are usually triggered at the start and end of work that
> is measured.
>
> Since OA buffer is large and queries can be frequent, an efficient way
> to look for triggered reports is required. By knowing the current head
> and tail offsets into the OA buffer, it is easier to determine the
> locality of the reports of interest.
>
> Current perf OA interface does not expose head/tail information to the
> user and it filters out invalid reports before sending data to user.
> Also considering limited size of user buffer used during a query,
> creating a 1:1 copy of the OA buffer at the user space added undesired
> complexity.
>
> The solution was to map the OA buffer to user space provided
>
> (1) that it is accessed from a privileged user.
> (2) OA report filtering is not used.
>
> These 2 conditions would satisfy the safety criteria that the current
> perf interface addresses.
>
> To enable the query:
> - Add an ioctl to expose head and tail to the user
> - Add an ioctl to return size and offset of the OA buffer
> - Map the OA buffer to the user space
>
> v2:
> - Improve commit message (Chris)
> - Do not mmap based on gem object filp. Instead, use perf_fd and support
> mmap syscall (Chris)
> - Pass non-zero offset in mmap to enforce the right object is
> mapped (Chris)
> - Do not expose gpu_address (Chris)
> - Verify start and length of vma for page alignment (Lionel)
> - Move SQNTL config out (Lionel)
>
> v3: (Chris)
> - Omit redundant checks
> - Return VM_FAULT_SIGBUS is old stream is closed
> - Maintain reference counts to stream in vm_open and vm_close
> - Use switch to identify object to be mapped
>
> v4: Call kref_put on closing perf fd (Chris)
> v5:
> - Strip access to OA buffer from unprivileged child of a privileged
> parent. Use VM_DONTCOPY
> - Enforce MAP_PRIVATE by checking for VM_MAYSHARE
>
> v6:
> (Chris)
> - Use len of -1 in unmap_mapping_range
> - Don't use stream->oa_buffer.vma->obj in vm_fault_oa
> - Use kernel block comment style
> - do_mmap gets a reference to the file and puts it in do_munmap, so
> no need to maintain a reference to i915_perf_stream. Hence, remove
> vm_open/vm_close and stream->closed hooks/checks.
> (Umesh)
> - Do not allow mmap if SAMPLE_OA_REPORT is not set during
> i915_perf_open_ioctl.
> - Drop ioctl returning head/tail since this information is already
> whitelisted. Remove hooks to read head register.
>
> v7: (Chris)
> - unmap before destroy
> - change ioctl argument struct
>
> v8: Documentation and more checks (Chris)
>
> Signed-off-by: Piotr Maciejewski <piotr.maciejewski@xxxxxxxxx>
> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
> ---
> +#define I915_PERF_OA_BUFFER_MMAP_OFFSET 1
> +
> +/**
> + * i915_perf_oa_buffer_info_locked - size and offset of the OA buffer
> + * @stream: i915 perf stream
> + * @arg: pointer to oa buffer info filled by this function.
> + */
> +static int i915_perf_oa_buffer_info_locked(struct i915_perf_stream *stream,
> + unsigned int cmd,
> + unsigned long arg)
> +{
> + struct drm_i915_perf_oa_buffer_info info;
> + void __user *output = (void __user *)arg;
> +
> + if (i915_perf_stream_paranoid && !perfmon_capable()) {
> + DRM_DEBUG("Insufficient privileges to access OA buffer info\n");
> + return -EACCES;
> + }
> +
> + if (_IOC_SIZE(cmd) != sizeof(info))
> + return -EINVAL;
For total pedantry, we could check cmd & (IOC_IN | IOC_OUT) as well :)
> +
> + if (copy_from_user(&info, output, sizeof(info)))
> + return -EFAULT;
> +
> + if (info.type || info.flags || info.rsvd)
> + return -EINVAL;
> +
> + info.size = stream->oa_buffer.vma->size;
> + info.offset = I915_PERF_OA_BUFFER_MMAP_OFFSET * PAGE_SIZE;
> +
> + if (copy_to_user(output, &info, sizeof(info)))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
> /**
> * i915_perf_ioctl - support ioctl() usage with i915 perf stream FDs
> * @stream: An i915 perf stream
> @@ -3290,6 +3329,8 @@ static long i915_perf_ioctl_locked(struct i915_perf_stream *stream,
> return 0;
> case I915_PERF_IOCTL_CONFIG:
> return i915_perf_config_locked(stream, arg);
> + case I915_PERF_IOCTL_GET_OA_BUFFER_INFO:
> + return i915_perf_oa_buffer_info_locked(stream, cmd, arg);
> }
>
> return -EINVAL;
> @@ -3361,6 +3402,14 @@ static int i915_perf_release(struct inode *inode, struct file *file)
> struct i915_perf_stream *stream = file->private_data;
> struct i915_perf *perf = stream->perf;
>
> + /*
> + * User could have multiple vmas from multiple mmaps. We want to zap
> + * them all here. Note that a fresh fault cannot occur as the mmap holds
> + * a reference to the stream via the vma->vm_file, so before user's
> + * munmap, the stream cannot be destroyed.
> + */
> + unmap_mapping_range(file->f_mapping, 0, -1, 1);
> +
> mutex_lock(&perf->lock);
> i915_perf_destroy_locked(stream);
> mutex_unlock(&perf->lock);
> @@ -3371,6 +3420,75 @@ static int i915_perf_release(struct inode *inode, struct file *file)
> return 0;
> }
>
> +static vm_fault_t vm_fault_oa(struct vm_fault *vmf)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct i915_perf_stream *stream = vma->vm_private_data;
> + int err;
> +
> + err = remap_io_sg(vma,
> + vma->vm_start, vma->vm_end - vma->vm_start,
> + stream->oa_buffer.vma->pages->sgl, -1);
> +
> + return i915_error_to_vmf_fault(err);
> +}
> +
> +static const struct vm_operations_struct vm_ops_oa = {
> + .fault = vm_fault_oa,
> +};
> +
> +static int i915_perf_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct i915_perf_stream *stream = file->private_data;
> +
> + /* mmap-ing OA buffer to user space MUST absolutely be privileged */
> + if (i915_perf_stream_paranoid && !perfmon_capable()) {
> + DRM_DEBUG("Insufficient privileges to map OA buffer\n");
> + return -EACCES;
> + }
> +
> + switch (vma->vm_pgoff) {
> + /*
> + * A non-zero offset ensures that we are mapping the right object. Also
> + * leaves room for future objects added to this implementation.
> + */
> + case I915_PERF_OA_BUFFER_MMAP_OFFSET:
> + if (!(stream->sample_flags & SAMPLE_OA_REPORT))
> + return -EINVAL;
> +
> + if (vma->vm_end - vma->vm_start > OA_BUFFER_SIZE)
> + return -EINVAL;
> +
> + /*
> + * Only support VM_READ. Enforce MAP_PRIVATE by checking for
> + * VM_MAYSHARE.
> + */
> + if (vma->vm_flags & (VM_WRITE | VM_EXEC |
> + VM_SHARED | VM_MAYSHARE))
> + return -EINVAL;
> +
> + vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC);
> +
> + /*
> + * If the privileged parent forks and child drops root
> + * privilege, we do not want the child to retain access to the
> + * mapped OA buffer. Explicitly set VM_DONTCOPY to avoid such
> + * cases.
> + */
> + vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND |
> + VM_DONTDUMP | VM_DONTCOPY;
> + break;
> +
> + default:
> + return -EINVAL;
> + }
> +
> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> + vma->vm_private_data = stream;
> + vma->vm_ops = &vm_ops_oa;
> +
> + return 0;
> +}
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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