drm/i915/guc: stop using kmap_atomic() during request submission

Now that we keep GuC shared objects mapped into kernel space for their
entire lifetime, we can simplify the code for accessing the doorbells
and work queue, which were previously calling kmap_atomic() on *each*
request submission.

This patch fixes the BUG shown below, where the thread could sleep
while holding the kmap_atomic mapping.

[   34.098798] BUG: scheduling while atomic:
gem_close_race/1941/0x00000002
[   34.098822] Modules linked in: hid_generic usbhid i915 asix usbnet
libphy mii i2c_algo_bit drm_kms_helper cfbfillrect syscopyarea cfbimgblt
sysfillrect sysimgblt fb_sys_fops cfbcopyarea drm coretemp i2c_hid hid
video pinctrl_sunrisepoint pinctrl_intel acpi_pad nls_iso8859_1 e1000e
ptp psmouse pps_core ahci libahci
[   34.098824] CPU: 0 PID: 1941 Comm: gem_close_race Tainted: G     U
          4.4.0-160121+ torvalds#123
[   34.098824] Hardware name: Intel Corporation Skylake Client
platform/Skylake AIO DDR3L RVP10, BIOS SKLSE2R1.R00.X100.B01.1509220551
09/22/2015
[   34.098825]  0000000000013e40 ffff880166c27a78 ffffffff81280d02
ffff880172c13e40
[   34.098826]  ffff880166c27a88 ffffffff810c203a ffff880166c27ac8
ffffffff814ec808
[   34.098827]  ffff88016b7c6000 ffff880166c28000 00000000000f4240
0000000000000001
[   34.098827] Call Trace:
[   34.098831]  [<ffffffff81280d02>] dump_stack+0x4b/0x79
[   34.098833]  [<ffffffff810c203a>] __schedule_bug+0x41/0x4f
[   34.098834]  [<ffffffff814ec808>] __schedule+0x5a8/0x690
[   34.098835]  [<ffffffff814ec927>] schedule+0x37/0x80
[   34.098836]  [<ffffffff814ef3fd>]
schedule_hrtimeout_range_clock+0xad/0x130
[   34.098837]  [<ffffffff81090be0>] ? hrtimer_init+0x10/0x10
[   34.098838]  [<ffffffff814ef3f1>] ?
schedule_hrtimeout_range_clock+0xa1/0x130
[   34.098839]  [<ffffffff814ef48e>] schedule_hrtimeout_range+0xe/0x10
[   34.098840]  [<ffffffff814eef9b>] usleep_range+0x3b/0x40
[   34.098853]  [<ffffffffa01ec109>] i915_guc_wq_check_space+0x119/0x210
[i915]
[   34.098861]  [<ffffffffa01da47c>]
intel_logical_ring_alloc_request_extras+0x5c/0x70 [i915]
[   34.098869]  [<ffffffffa01cdbf1>] i915_gem_request_alloc+0x91/0x170
[i915]
[   34.098875]  [<ffffffffa01c1c07>]
i915_gem_do_execbuffer.isra.25+0xbc7/0x12a0 [i915]
[   34.098882]  [<ffffffffa01cb785>] ?
i915_gem_object_get_pages_gtt+0x225/0x3c0 [i915]
[   34.098889]  [<ffffffffa01d1fb6>] ? i915_gem_pwrite_ioctl+0xd6/0x9f0
[i915]
[   34.098895]  [<ffffffffa01c2e68>] i915_gem_execbuffer2+0xa8/0x250
[i915]
[   34.098900]  [<ffffffffa00f65d8>] drm_ioctl+0x258/0x4f0 [drm]
[   34.098906]  [<ffffffffa01c2dc0>] ? i915_gem_execbuffer+0x340/0x340
[i915]
[   34.098908]  [<ffffffff8111590d>] do_vfs_ioctl+0x2cd/0x4a0
[   34.098909]  [<ffffffff8111eac2>] ? __fget+0x72/0xb0
[   34.098910]  [<ffffffff81115b1c>] SyS_ioctl+0x3c/0x70
[   34.098911]  [<ffffffff814effd7>] entry_SYSCALL_64_fastpath+0x12/0x6a
[   34.100208] ------------[ cut here ]------------

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93847
Cc: <daniel.vetter@ffwll.ch>
Cc: <tvrtko.ursulin@intel.com>
Signed-off-by: Alex Dai <yu.dai@intel.com>
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -191,11 +191,9 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 	struct guc_process_desc *desc;
 	union guc_doorbell_qw db_cmp, db_exc, db_ret;
 	union guc_doorbell_qw *db;
-	void *base;
 	int attempt = 2, ret = -EAGAIN;
 
-	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj, 0));
-	desc = base + gc->proc_desc_offset;
+	desc = gc->client_base + gc->proc_desc_offset;
 
 	/* Update the tail so it is visible to GuC */
 	desc->tail = gc->wq_tail;
@@ -211,7 +209,7 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 		db_exc.cookie = 1;
 
 	/* pointer of current doorbell cacheline */
-	db = base + gc->doorbell_offset;
+	db = gc->client_base + gc->doorbell_offset;
 
 	while (attempt--) {
 		/* lets ring the doorbell */
@@ -243,7 +241,6 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 	/* Finally, update the cached copy of the GuC's WQ head */
 	gc->wq_head = desc->head;
 
-	kunmap_atomic(base);
 	return ret;
 }
 
@@ -462,7 +459,6 @@ static void guc_fini_ctx_desc(struct intel_guc *guc,
 int i915_guc_wq_check_space(struct i915_guc_client *gc)
 {
 	struct guc_process_desc *desc;
-	void *base;
 	u32 size = sizeof(struct guc_wq_item);
 	int ret = -ETIMEDOUT, timeout_counter = 200;
 
@@ -474,8 +470,7 @@ int i915_guc_wq_check_space(struct i915_guc_client *gc)
 	if (CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size) >= size)
 		return 0;
 
-	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj, 0));
-	desc = base + gc->proc_desc_offset;
+	desc = gc->client_base + gc->proc_desc_offset;
 
 	while (timeout_counter-- > 0) {
 		gc->wq_head = desc->head;
@@ -489,16 +484,13 @@ int i915_guc_wq_check_space(struct i915_guc_client *gc)
 			usleep_range(1000, 2000);
 	};
 
-	kunmap_atomic(base);
-
 	return ret;
 }
 
 static int guc_add_workqueue_item(struct i915_guc_client *gc,
 				  struct drm_i915_gem_request *rq)
 {
 	struct guc_wq_item *wqi;
-	void *base;
 	u32 tail, wq_len, wq_off, space;
 
 	space = CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size);
@@ -521,10 +513,7 @@ static int guc_add_workqueue_item(struct i915_guc_client *gc,
 	WARN_ON(wq_off & 3);
 
 	/* wq starts from the page after doorbell / process_desc */
-	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj,
-			(wq_off + GUC_DB_SIZE) >> PAGE_SHIFT));
-	wq_off &= PAGE_SIZE - 1;
-	wqi = (struct guc_wq_item *)((char *)base + wq_off);
+	wqi = gc->client_base + GUC_DB_SIZE + wq_off;
 
 	/* len does not include the header */
 	wq_len = sizeof(struct guc_wq_item) / sizeof(u32) - 1;
@@ -542,8 +531,6 @@ static int guc_add_workqueue_item(struct i915_guc_client *gc,
 	wqi->ring_tail = tail << WQ_RING_TAIL_SHIFT;
 	wqi->fence_id = 0; /*XXX: what fence to be here */
 
-	kunmap_atomic(base);
-
 	return 0;
 }