drm/amdgpu: fix stall on CPU when allocate large system memory

-v2: 1. rename variable to redue confuse
     2. optimize the code
-v3: move new define out of the middle of the code
-v4: squash in minmax error fix (Luben)

When applications try to allocate large system (more than > 128GB),
"stall cpu" is reported.

for such large system memory, walk_page_range takes more than 20s usually.
The warning message can be removed when splitting hmm range into smaller
ones which is not more 64GB for each walk_page_range.

[  164.437617] amdgpu:amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu:1753: amdgpu: 	create BO VA 0x7f63c7a00000 size 0x2f16000000 domain CPU
[  164.488847] amdgpu:amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu:1785: amdgpu: creating userptr BO for user_addr = 7f63c7a00000
[  185.439116] rcu: INFO: rcu_sched self-detected stall on CPU
[  185.439125] rcu: 	8-....: (20999 ticks this GP) idle=e22/1/0x4000000000000000 softirq=2242/2242 fqs=5249
[  185.439137] 	(t=21000 jiffies g=6325 q=1215)
[  185.439141] NMI backtrace for cpu 8
[  185.439143] CPU: 8 PID: 3470 Comm: kfdtest Kdump: loaded Tainted: G           O      5.12.0-0_fbk5_zion_rc1_5697_g2c723fb88626 #1
[  185.439147] Hardware name: HPE ProLiant XL675d Gen10 Plus/ProLiant XL675d Gen10 Plus, BIOS A47 11/06/2020
[  185.439150] Call Trace:
[  185.439153]  <IRQ>
[  185.439157]  dump_stack+0x64/0x7c
[  185.439163]  nmi_cpu_backtrace.cold.7+0x30/0x65
[  185.439165]  ? lapic_can_unplug_cpu+0x70/0x70
[  185.439170]  nmi_trigger_cpumask_backtrace+0xf9/0x100
[  185.439174]  rcu_dump_cpu_stacks+0xc5/0xf5
[  185.439178]  rcu_sched_clock_irq.cold.97+0x112/0x38c
[  185.439182]  ? tick_sched_handle.isra.21+0x50/0x50
[  185.439185]  update_process_times+0x8c/0xc0
[  185.439189]  tick_sched_timer+0x63/0x70
[  185.439192]  __hrtimer_run_queues+0xff/0x250
[  185.439195]  hrtimer_interrupt+0xf4/0x200
[  185.439199]  __sysvec_apic_timer_interrupt+0x51/0xd0
[  185.439201]  sysvec_apic_timer_interrupt+0x69/0x90
[  185.439206]  </IRQ>
[  185.439207]  asm_sysvec_apic_timer_interrupt+0x12/0x20
[  185.439211] RIP: 0010:clear_page_rep+0x7/0x10
[  185.439214] Code: e8 fe 7c 51 00 44 89 e2 48 89 ee 48 89 df e8 60 ff ff ff c6 03 00 5b 5d 41 5c c3 cc cc cc cc cc cc cc cc b9 00 02 00 00 31 c0 <f3> 48 ab c3 0f 1f 44 00 00 31 c0 b9 40 00 00 00 66 0f 1f 84 00 00
[  185.439218] RSP: 0018:ffffc9000f58f818 EFLAGS: 00000246
[  185.439220] RAX: 0000000000000000 RBX: 0000000000000881 RCX: 000000000000005c
[  185.439223] RDX: 0000000000100dca RSI: 0000000000000000 RDI: ffff88a59e0e5d20
[  185.439225] RBP: ffffea0096783940 R08: ffff888118c35280 R09: ffffea0096783940
[  185.439227] R10: ffff888000000000 R11: 0000160000000000 R12: ffffea0096783980
[  185.439228] R13: ffffea0096783940 R14: ffff88b07fdfdd00 R15: 0000000000000000
[  185.439232]  prep_new_page+0x81/0xc0
[  185.439236]  get_page_from_freelist+0x13be/0x16f0
[  185.439240]  ? release_pages+0x16a/0x4a0
[  185.439244]  __alloc_pages_nodemask+0x1ae/0x340
[  185.439247]  alloc_pages_vma+0x74/0x1e0
[  185.439251]  __handle_mm_fault+0xafe/0x1360
[  185.439255]  handle_mm_fault+0xc3/0x280
[  185.439257]  hmm_vma_fault.isra.22+0x49/0x90
[  185.439261]  __walk_page_range+0x692/0x9b0
[  185.439265]  walk_page_range+0x9b/0x120
[  185.439269]  hmm_range_fault+0x4f/0x90
[  185.439274]  amdgpu_hmm_range_get_pages+0x24f/0x260 [amdgpu]
[  185.439463]  amdgpu_ttm_tt_get_user_pages+0xc2/0x190 [amdgpu]
[  185.439603]  amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu+0x49f/0x7a0 [amdgpu]
[  185.439774]  kfd_ioctl_alloc_memory_of_gpu+0xfb/0x410 [amdgpu]
Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c

@@ -51,6 +51,8 @@
 #include "amdgpu_amdkfd.h"
 #include "amdgpu_hmm.h"
 
+#define MAX_WALK_BYTE	(2UL << 30)
+
 /**
  * amdgpu_hmm_invalidate_gfx - callback to notify about mm change
  *
@@ -163,6 +165,7 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
 			       struct hmm_range **phmm_range)
 {
 	struct hmm_range *hmm_range;
+	unsigned long end;
 	unsigned long timeout;
 	unsigned long i;
 	unsigned long *pfns;
@@ -184,11 +187,18 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
 		hmm_range->default_flags |= HMM_PFN_REQ_WRITE;
 	hmm_range->hmm_pfns = pfns;
 	hmm_range->start = start;
-	hmm_range->end = start + npages * PAGE_SIZE;
+	end = start + npages * PAGE_SIZE;
 	hmm_range->dev_private_owner = owner;
 
+	do {
+		hmm_range->end = min(hmm_range->start + MAX_WALK_BYTE, end);
+
+		pr_debug("hmm range: start = 0x%lx, end = 0x%lx",
+			hmm_range->start, hmm_range->end);
+
 		/* Assuming 512MB takes maxmium 1 second to fault page address */
-	timeout = max(npages >> 17, 1ULL) * HMM_RANGE_DEFAULT_TIMEOUT;
+		timeout = max((hmm_range->end - hmm_range->start) >> 29, 1UL);
+		timeout *= HMM_RANGE_DEFAULT_TIMEOUT;
 		timeout = jiffies + msecs_to_jiffies(timeout);
 
 retry:
@@ -204,6 +214,16 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier,
 			goto out_free_pfns;
 		}
 
+		if (hmm_range->end == end)
+			break;
+		hmm_range->hmm_pfns += MAX_WALK_BYTE >> PAGE_SHIFT;
+		hmm_range->start = hmm_range->end;
+		schedule();
+	} while (hmm_range->end < end);
+
+	hmm_range->start = start;
+	hmm_range->hmm_pfns = pfns;
+
 	/*
 	 * Due to default_flags, all pages are HMM_PFN_VALID or
 	 * hmm_range_fault() fails. FIXME: The pages cannot be touched outside