On 26/07/2021 16:14, Jason Ekstrand wrote:
On Mon, Jul 26, 2021 at 3:31 AM Maarten Lankhorst
<maarten.lankhorst@xxxxxxxxxxxxxxx> wrote:
Op 23-07-2021 om 13:34 schreef Matthew Auld:
From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Jason Ekstrand requested a more efficient method than userptr+set-domain
to determine if the userptr object was backed by a complete set of pages
upon creation. To be more efficient than simply populating the userptr
using get_user_pages() (as done by the call to set-domain or execbuf),
we can walk the tree of vm_area_struct and check for gaps or vma not
backed by struct page (VM_PFNMAP). The question is how to handle
VM_MIXEDMAP which may be either struct page or pfn backed...
With discrete we are going to drop support for set_domain(), so offering
a way to probe the pages, without having to resort to dummy batches has
been requested.
v2:
- add new query param for the PROBE flag, so userspace can easily
check if the kernel supports it(Jason).
- use mmap_read_{lock, unlock}.
- add some kernel-doc.
v3:
- In the docs also mention that PROBE doesn't guarantee that the pages
will remain valid by the time they are actually used(Tvrtko).
- Add a small comment for the hole finding logic(Jason).
- Move the param next to all the other params which just return true.
Testcase: igt/gem_userptr_blits/probe
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Jordan Justen <jordan.l.justen@xxxxxxxxx>
Cc: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Ramalingam C <ramalingam.c@xxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Acked-by: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
Reviewed-by: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 41 ++++++++++++++++++++-
drivers/gpu/drm/i915/i915_getparam.c | 1 +
include/uapi/drm/i915_drm.h | 20 ++++++++++
3 files changed, 61 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 56edfeff8c02..468a7a617fbf 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -422,6 +422,34 @@ static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
#endif
+static int
+probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
+{
+ const unsigned long end = addr + len;
+ struct vm_area_struct *vma;
+ int ret = -EFAULT;
+
+ mmap_read_lock(mm);
+ for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
+ /* Check for holes, note that we also update the addr below */
+ if (vma->vm_start > addr)
+ break;
+
+ if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+ break;
+
+ if (vma->vm_end >= end) {
+ ret = 0;
+ break;
+ }
+
+ addr = vma->vm_end;
+ }
+ mmap_read_unlock(mm);
+
+ return ret;
+}
+
/*
* Creates a new mm object that wraps some normal memory from the process
* context - user memory.
@@ -477,7 +505,8 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
}
if (args->flags & ~(I915_USERPTR_READ_ONLY |
- I915_USERPTR_UNSYNCHRONIZED))
+ I915_USERPTR_UNSYNCHRONIZED |
+ I915_USERPTR_PROBE))
return -EINVAL;
if (i915_gem_object_size_2big(args->user_size))
@@ -504,6 +533,16 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
return -ENODEV;
}
+ if (args->flags & I915_USERPTR_PROBE) {
+ /*
+ * Check that the range pointed to represents real struct
+ * pages and not iomappings (at this moment in time!)
+ */
+ ret = probe_range(current->mm, args->user_ptr, args->user_size);
+ if (ret)
+ return ret;
+ }
+
#ifdef CONFIG_MMU_NOTIFIER
obj = i915_gem_object_alloc();
if (obj == NULL)
diff --git a/drivers/gpu/drm/i915/i915_getparam.c b/drivers/gpu/drm/i915/i915_getparam.c
index 24e18219eb50..bbb7cac43eb4 100644
--- a/drivers/gpu/drm/i915/i915_getparam.c
+++ b/drivers/gpu/drm/i915/i915_getparam.c
@@ -134,6 +134,7 @@ int i915_getparam_ioctl(struct drm_device *dev, void *data,
case I915_PARAM_HAS_EXEC_FENCE_ARRAY:
case I915_PARAM_HAS_EXEC_SUBMIT_FENCE:
case I915_PARAM_HAS_EXEC_TIMELINE_FENCES:
+ case I915_PARAM_HAS_USERPTR_PROBE:
/* For the time being all of these are always true;
* if some supported hardware does not have one of these
* features this value needs to be provided from
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 975087553ea0..0d290535a6e5 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -674,6 +674,9 @@ typedef struct drm_i915_irq_wait {
*/
#define I915_PARAM_HAS_EXEC_TIMELINE_FENCES 55
+/* Query if the kernel supports the I915_USERPTR_PROBE flag. */
+#define I915_PARAM_HAS_USERPTR_PROBE 56
+
/* Must be kept compact -- no holes and well documented */
typedef struct drm_i915_getparam {
@@ -2222,12 +2225,29 @@ struct drm_i915_gem_userptr {
* through the GTT. If the HW can't support readonly access, an error is
* returned.
*
+ * I915_USERPTR_PROBE:
+ *
+ * Probe the provided @user_ptr range and validate that the @user_ptr is
+ * indeed pointing to normal memory and that the range is also valid.
+ * For example if some garbage address is given to the kernel, then this
+ * should complain.
+ *
+ * Returns -EFAULT if the probe failed.
+ *
+ * Note that this doesn't populate the backing pages, and also doesn't
+ * guarantee that the object will remain valid when the object is
+ * eventually used.
+ *
+ * The kernel supports this feature if I915_PARAM_HAS_USERPTR_PROBE
+ * returns a non-zero value.
+ *
* I915_USERPTR_UNSYNCHRONIZED:
*
* NOT USED. Setting this flag will result in an error.
*/
__u32 flags;
#define I915_USERPTR_READ_ONLY 0x1
+#define I915_USERPTR_PROBE 0x2
#define I915_USERPTR_UNSYNCHRONIZED 0x80000000
/**
* @handle: Returned handle for the object.
Could we use _VALIDATE instead of probe? Or at least pin the pages as well, so we don't have to do it later?
I only care that the name matches what it does. _VALIDATE sounds like
it does a full validation of everything such that, if the import
succeeds, execbuf will as well. If we pin the pages at the same time,
maybe that's true? _PROBE, on the other hand, sounds a lot more like
No it is not possible to guarantee backing store remains valid until
execbuf.
a one-time best-effort check which may race with other stuff and
doesn't guarantee future success. That's in line with what the
current patch does.
We already have i915_gem_object_userptr_validate, no need to dupe it.
I have no opinion on this.
I was actually suggesting the same as Maarten here - that we should add
a "populate" flag. But opinion was that was not desired - please look
for the older threads to see the reasoning there.
Regards,
Tvrtko
