Quoting Umesh Nerlige Ramappa (2020-07-21 03:17:59)
> Hi Chris,
>
> I have added your comments, but I have a few questions below:
>
> Thanks for your help,
> Umesh
>
> On Mon, Jul 20, 2020 at 07:00:12PM -0700, Umesh Nerlige Ramappa wrote:
> >From: Piotr Maciejewski <piotr.maciejewski@xxxxxxxxx>
> >+static void vm_open_oa(struct vm_area_struct *vma)
> >+{
> >+ struct i915_perf_stream *stream = vma->vm_private_data;
> >+
> >+ GEM_BUG_ON(!stream);
> >+ kref_get(&stream->refcount);
>
> When user calls mmap, after this call the count is 2 (since kref_init
> started off the count with 1).
>
> >+}
> >+
> >+static void vm_close_oa(struct vm_area_struct *vma)
> >+{
> >+ struct i915_perf_stream *stream = vma->vm_private_data;
> >+
> >+ GEM_BUG_ON(!stream);
> >+ kref_put(&stream->refcount, free_stream);
>
> When the user closes perf fd or calls unmap, vm_close_oa is called and
> refcount goes to 1, so not sure how the refcount goes to 0 so that
> free_stream is called. Should I kref_put when closing perf fd also?
Yes, at a glance, I would say i915_perf_destroy_locked() should replace
the kfree(stream) with a kref_put.
> >+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;
> >+ struct drm_i915_gem_object *obj = stream->oa_buffer.vma->obj;
> >+ int err;
> >+
> >+ if (READ_ONCE(stream->closed))
> >+ return VM_FAULT_SIGBUS;
> >+
> >+ err = i915_gem_object_pin_pages(obj);
> >+ if (err)
> >+ goto out;
> >+
> >+ err = remap_io_sg(vma,
> >+ vma->vm_start, vma->vm_end - vma->vm_start,
> >+ obj->mm.pages->sgl, -1);
> >+
> >+ i915_gem_object_unpin_pages(obj);
> >+
> >+out:
> >+ return i915_error_to_vmf_fault(err);
> >+}
> >+
> >+static const struct vm_operations_struct vm_ops_oa = {
> >+ .open = vm_open_oa,
> >+ .close = vm_close_oa,
> >+ .fault = vm_fault_oa,
> >+};
> >+
> >+int i915_perf_mmap(struct file *file, struct vm_area_struct *vma)
> >+{
> >+ struct i915_perf_stream *stream = file->private_data;
> >+
> >+ if (i915_perf_stream_paranoid && !perfmon_capable()) {
> >+ DRM_DEBUG("Insufficient privileges to map OA buffer\n");
> >+ return -EACCES;
> >+ }
> >+
> >+ switch (vma->vm_pgoff) {
> >+ case I915_PERF_OA_BUFFER_MMAP_OFFSET:
> >+ if (vma->vm_end - vma->vm_start > OA_BUFFER_SIZE)
> >+ return -EINVAL;
> >+
> >+ if (vma->vm_flags & VM_WRITE)
> >+ return -EINVAL;
> >+
> >+ break;
> >+
> >+ default:
> >+ return -EINVAL;
> >+ }
> >+
> >+ vma->vm_flags &= ~(VM_MAYWRITE | VM_MAYEXEC | VM_MAYSHARE);
> >+ vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
> >+ vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> >+ vma->vm_private_data = stream;
> >+ vma->vm_ops = &vm_ops_oa;
> >+ vm_open_oa(vma);
>
> I am calling the open explicitly here to get the reference, otherwise I
> don't see open being called by anyone/anything.
The initial vm_ops->open is implicit, i.e. the mmap starts opened, and
the vm_ops->open() is only called when the vma is cloned (e.g. on
fork()).
> If user calls mmap multiple times, does he get a unique vma each time?
Yes.
> Do I need to track all of them (and their sizes) and then unmap them
> when perf_fd is closed?
Yes... But we can zap them all with a single unmap_mapping_range() call,
since they all exist within the perf_fd->f_mapping.
> >diff --git a/drivers/gpu/drm/i915/i915_perf_types.h b/drivers/gpu/drm/i915/i915_perf_types.h
> >index a36a455ae336..2efbe35c5fa9 100644
> >--- a/drivers/gpu/drm/i915/i915_perf_types.h
> >+++ b/drivers/gpu/drm/i915/i915_perf_types.h
> >@@ -311,6 +311,18 @@ struct i915_perf_stream {
> > * buffer should be checked for available data.
> > */
> > u64 poll_oa_period;
> >+
> >+ /**
> >+ * @closed: Open or closed state of the stream.
> >+ * True if stream is closed.
> >+ */
> >+ bool closed;
>
> closed is part of the stream itself, so I cannot kfree(stream) until the
> refcount goes to 0.
Correct. kfree must be part of the kref_put cb.
> >+ /**
> >+ * @refcount: References to the mapped OA buffer managed by this
> >+ * stream.
> >+ */
> >+ struct kref refcount;
> > };
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