Re: [Intel-gfx] [PATCH 1/3] drm/i915: Move user fault tracking to a separate list

2016-10-13 Thread Daniel Vetter 
On Tue, Oct 11, 2016 at 03:37:57PM +0100, Chris Wilson wrote:
> We want to decouple RPM and struct_mutex, but currently RPM has to walk
> the list of bound objects and remove userspace mmapping before we
> suspend (otherwise userspace may continue to access the GTT whilst it is
> powered down). This currently requires the struct_mutex to walk the
> bound_list, but if we move that to a separate list and lock we can take
> the first step towards removing the struct_mutex.
> 
> Signed-off-by: Chris Wilson 
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c   |  4 ++--
>  drivers/gpu/drm/i915/i915_drv.h   | 20 +++---
>  drivers/gpu/drm/i915/i915_gem.c   | 39 
> +++
>  drivers/gpu/drm/i915/i915_gem_evict.c |  2 +-
>  4 files changed, 46 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c 
> b/drivers/gpu/drm/i915/i915_debugfs.c
> index 358663e833d6..d4ecc5283c2a 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -186,11 +186,11 @@ describe_obj(struct seq_file *m, struct 
> drm_i915_gem_object *obj)
>   }
>   if (obj->stolen)
>   seq_printf(m, " (stolen: %08llx)", obj->stolen->start);
> - if (obj->pin_display || obj->fault_mappable) {
> + if (obj->pin_display || !list_empty(>userfault_link)) {
>   char s[3], *t = s;
>   if (obj->pin_display)
>   *t++ = 'p';
> - if (obj->fault_mappable)
> + if (!list_empty(>userfault_link))
>   *t++ = 'f';
>   *t = '\0';
>   seq_printf(m, " (%s mappable)", s);
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index bf397b643cc0..72b3126c6c74 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1359,6 +1359,14 @@ struct i915_gem_mm {
>*/
>   struct list_head unbound_list;
>  
> + /** Protects access to the userfault_list */
> + spinlock_t userfault_lock;
> +
> + /** List of all objects in gtt_space, currently mmaped by userspace.
> +  * All objects within this list must also be on bound_list.
> +  */
> + struct list_head userfault_list;
> +
>   /** Usable portion of the GTT for GEM */
>   unsigned long stolen_base; /* limited to low memory (32-bit) */
>  
> @@ -2215,6 +2223,11 @@ struct drm_i915_gem_object {
>   struct drm_mm_node *stolen;
>   struct list_head global_list;
>  
> + /**
> +  * Whether the object is currently in the GGTT mmap.
> +  */
> + struct list_head userfault_link;
> +
>   /** Used in execbuf to temporarily hold a ref */
>   struct list_head obj_exec_link;
>  
> @@ -2242,13 +2255,6 @@ struct drm_i915_gem_object {
>*/
>   unsigned int madv:2;
>  
> - /**
> -  * Whether the current gtt mapping needs to be mappable (and isn't just
> -  * mappable by accident). Track pin and fault separate for a more
> -  * accurate mappable working set.
> -  */
> - unsigned int fault_mappable:1;
> -
>   /*
>* Is the object to be mapped as read-only to the GPU
>* Only honoured if hardware has relevant pte bit
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index fdd496e6c081..91910ffe0964 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1850,7 +1850,10 @@ int i915_gem_fault(struct vm_area_struct *area, struct 
> vm_fault *vmf)
>   if (ret)
>   goto err_unpin;
>  
> - obj->fault_mappable = true;
> + spin_lock(_priv->mm.userfault_lock);
> + list_add(>userfault_link, _priv->mm.userfault_list);
> + spin_unlock(_priv->mm.userfault_lock);

I think we need to add it to the list _before_ we start punching in new
ptes. At least if we want to decouple the locking and rpm refcounting a
lot more (which I think we should, I had magic locks that ensure ordering
on their own simply by being a BKL). But right now it's ok, so just a
bikeshed.

> +
>  err_unpin:
>   __i915_vma_unpin(vma);
>  err_unlock:
> @@ -1918,36 +1921,52 @@ err:
>  void
>  i915_gem_release_mmap(struct drm_i915_gem_object *obj)
>  {
> + struct drm_i915_private *i915 = to_i915(obj->base.dev);
> + bool zap = false;
> +
>   /* Serialisation between user GTT access and our code depends upon
>* revoking the CPU's PTE whilst the mutex is held. The next user
>* pagefault then has to wait until we release the mutex.
> +  *
> +  * Note that RPM complicates somewhat by adding an additional
> +  * requirement that operations to the GGTT be made holding the RPM
> +  * wakeref.
>*/
>   lockdep_assert_held(>base.dev->struct_mutex);
>  
> - if (!obj->fault_mappable)
> + spin_lock(>mm.userfault_lock);
> + if (!list_empty(>userfault_link)) {
> +

[Intel-gfx] [PATCH 1/3] drm/i915: Move user fault tracking to a separate list

2016-10-11 Thread Chris Wilson 
We want to decouple RPM and struct_mutex, but currently RPM has to walk
the list of bound objects and remove userspace mmapping before we
suspend (otherwise userspace may continue to access the GTT whilst it is
powered down). This currently requires the struct_mutex to walk the
bound_list, but if we move that to a separate list and lock we can take
the first step towards removing the struct_mutex.

Signed-off-by: Chris Wilson 
---
 drivers/gpu/drm/i915/i915_debugfs.c   |  4 ++--
 drivers/gpu/drm/i915/i915_drv.h   | 20 +++---
 drivers/gpu/drm/i915/i915_gem.c   | 39 +++
 drivers/gpu/drm/i915/i915_gem_evict.c |  2 +-
 4 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c 
b/drivers/gpu/drm/i915/i915_debugfs.c
index 358663e833d6..d4ecc5283c2a 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -186,11 +186,11 @@ describe_obj(struct seq_file *m, struct 
drm_i915_gem_object *obj)
}
if (obj->stolen)
seq_printf(m, " (stolen: %08llx)", obj->stolen->start);
-   if (obj->pin_display || obj->fault_mappable) {
+   if (obj->pin_display || !list_empty(>userfault_link)) {
char s[3], *t = s;
if (obj->pin_display)
*t++ = 'p';
-   if (obj->fault_mappable)
+   if (!list_empty(>userfault_link))
*t++ = 'f';
*t = '\0';
seq_printf(m, " (%s mappable)", s);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bf397b643cc0..72b3126c6c74 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1359,6 +1359,14 @@ struct i915_gem_mm {
 */
struct list_head unbound_list;
 
+   /** Protects access to the userfault_list */
+   spinlock_t userfault_lock;
+
+   /** List of all objects in gtt_space, currently mmaped by userspace.
+* All objects within this list must also be on bound_list.
+*/
+   struct list_head userfault_list;
+
/** Usable portion of the GTT for GEM */
unsigned long stolen_base; /* limited to low memory (32-bit) */
 
@@ -2215,6 +2223,11 @@ struct drm_i915_gem_object {
struct drm_mm_node *stolen;
struct list_head global_list;
 
+   /**
+* Whether the object is currently in the GGTT mmap.
+*/
+   struct list_head userfault_link;
+
/** Used in execbuf to temporarily hold a ref */
struct list_head obj_exec_link;
 
@@ -2242,13 +2255,6 @@ struct drm_i915_gem_object {
 */
unsigned int madv:2;
 
-   /**
-* Whether the current gtt mapping needs to be mappable (and isn't just
-* mappable by accident). Track pin and fault separate for a more
-* accurate mappable working set.
-*/
-   unsigned int fault_mappable:1;
-
/*
 * Is the object to be mapped as read-only to the GPU
 * Only honoured if hardware has relevant pte bit
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fdd496e6c081..91910ffe0964 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1850,7 +1850,10 @@ int i915_gem_fault(struct vm_area_struct *area, struct 
vm_fault *vmf)
if (ret)
goto err_unpin;
 
-   obj->fault_mappable = true;
+   spin_lock(_priv->mm.userfault_lock);
+   list_add(>userfault_link, _priv->mm.userfault_list);
+   spin_unlock(_priv->mm.userfault_lock);
+
 err_unpin:
__i915_vma_unpin(vma);
 err_unlock:
@@ -1918,36 +1921,52 @@ err:
 void
 i915_gem_release_mmap(struct drm_i915_gem_object *obj)
 {
+   struct drm_i915_private *i915 = to_i915(obj->base.dev);
+   bool zap = false;
+
/* Serialisation between user GTT access and our code depends upon
 * revoking the CPU's PTE whilst the mutex is held. The next user
 * pagefault then has to wait until we release the mutex.
+*
+* Note that RPM complicates somewhat by adding an additional
+* requirement that operations to the GGTT be made holding the RPM
+* wakeref.
 */
lockdep_assert_held(>base.dev->struct_mutex);
 
-   if (!obj->fault_mappable)
+   spin_lock(>mm.userfault_lock);
+   if (!list_empty(>userfault_link)) {
+   list_del_init(>userfault_link);
+   zap = true;
+   }
+   spin_unlock(>mm.userfault_lock);
+   if (!zap)
return;
 
drm_vma_node_unmap(>base.vma_node,
   obj->base.dev->anon_inode->i_mapping);
 
/* Ensure that the CPU's PTE are revoked and there are not outstanding
-* memory transactions from userspace before we return. The TLB
-* flushing implied above by changing the PTE above *should* be
+