If GUP-ineligible pages are passed to a GEM userptr object, -EFAULT is returned only when the object is actually bound.
The xf86-video-intel userspace driver cannot differentiate this
condition, and marks the GPU as wedged. This disables graphics
acceleration and may cripple other functionalities such as VT switch.
Solve this by "prefaulting" user pages on GEM object creation, testing
whether all pages are eligible for get_user_pages() in the process.
On failure, return -EFAULT so that userspace can fallback to software
bliting.
This behavior can be controlled by using a new modparam
"gem_userptr_prefault", which is true by default.
The only known use for this patch is Qubes OS's GUI virtualization.
Userspace is expected to resort to DMA-BUF whenever possible.
Signed-off-by: Jinoh Kang <jinoh.kang...@gmail.com>
---
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 36 +++++++++++++++++++++
drivers/gpu/drm/i915/i915_params.c | 3 ++
drivers/gpu/drm/i915/i915_params.h | 1 +
3 files changed, 40 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 6d0cc90401c0..c86862a6f592 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -739,6 +739,34 @@ static const struct drm_i915_gem_object_ops
i915_gem_userptr_ops = {
.release = i915_gem_userptr_release,
};
+static int i915_gem_userptr_prefault(unsigned long start,
+ unsigned long nr_pages,
+ bool readonly)
+{
+ struct mm_struct *mm = current->mm;
+ unsigned int gup_flags = (readonly ? 0 : FOLL_WRITE) | FOLL_NOWAIT;
+ int err = 0;
+
+ down_read(&mm->mmap_sem);
+ while (nr_pages) {
+ long ret;
+
+ ret = get_user_pages(start, nr_pages, gup_flags, NULL, NULL);
+ if (ret < 0) {
+ err = (int)ret;
+ break;
+ }
+ if (ret == 0)
+ ret = 1; /* skip this page */
+
+ start += ret << PAGE_SHIFT;
+ nr_pages -= ret;
+ }
+ up_read(&mm->mmap_sem);
+
+ return err;
+}
+
/*
* Creates a new mm object that wraps some normal memory from the process
* context - user memory.
@@ -805,6 +833,14 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
if (!access_ok((char __user *)(unsigned long)args->user_ptr,
args->user_size))
return -EFAULT;
+ if (READ_ONCE(i915_modparams.gem_userptr_prefault)) {
+ ret = i915_gem_userptr_prefault((unsigned long)args->user_ptr,
+ args->user_size >> PAGE_SHIFT,
+ args->flags &
I915_USERPTR_READ_ONLY);
+ if (ret)
+ return ret;
+ }
+
if (args->flags & I915_USERPTR_READ_ONLY) {
struct i915_address_space *vm;
diff --git a/drivers/gpu/drm/i915/i915_params.c
b/drivers/gpu/drm/i915/i915_params.c
index 296452f9efe4..90a03cb8ca57 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -178,6 +178,9 @@ i915_param_named(enable_gvt, bool, 0400,
"Enable support for Intel GVT-g graphics virtualization host
support(default:false)");
#endif
+i915_param_named(gem_userptr_prefault, bool, 0600,
+ "Prefault pages when userptr GEM object is created (default:true)");
+
static __always_inline void _print_param(struct drm_printer *p,
const char *name,
const char *type,
diff --git a/drivers/gpu/drm/i915/i915_params.h
b/drivers/gpu/drm/i915/i915_params.h
index d29ade3b7de6..c64866c256a3 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -76,6 +76,7 @@ struct drm_printer;
param(bool, disable_display, false) \
param(bool, verbose_state_checks, true) \
param(bool, nuclear_pageflip, false) \
+ param(bool, gem_userptr_prefault, true) \
param(bool, enable_dp_mst, true) \
param(bool, enable_gvt, false)
--
2.26.2
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