Nouveau - Mar 2020 - [PATCH 3/4] mm: simplify device private page handling in hmm_range_fault

Adding linux-kselftest at vger.kernel.org for the test config question.

On 3/19/20 11:17 AM, Jason Gunthorpe wrote:
> On Tue, Mar 17, 2020 at 04:14:31PM -0700, Ralph Campbell wrote:
>>
>> On 3/17/20 5:59 AM, Christoph Hellwig wrote:
>>> On Tue, Mar 17, 2020 at 09:47:55AM -0300, Jason Gunthorpe wrote:
>>>> I've been using v7 of Ralph's tester and it is working
well - it has
>>>> DEVICE_PRIVATE support so I think it can test this flow too.
Ralph are
>>>> you able?
>>>>
>>>> This hunk seems trivial enough to me, can we include it now?
>>>
>>> I can send a separate patch for it once the tester covers it.  I
don't
>>> want to add it to the original patch as it is a significant
behavior
>>> change compared to the existing code.
>>>
>>
>> Attached is an updated version of my HMM tests based on
linux-5.6.0-rc6.
>> I ran this OK with Jason's 8+1 HMM patches, Christoph's 1-5
misc HMM clean ups,
>> and Christoph's 1-4 device private page changes applied.
> 
> I'd like to get this to mergable, it looks pretty good now, but I have
> no idea about selftests - and I'm struggling to even compile the tools
> dir
> 
>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>> index 69def4a9df00..4d22ce7879a7 100644
>> +++ b/lib/Kconfig.debug
>> @@ -2162,6 +2162,18 @@ config TEST_MEMINIT
>>   
>>   	  If unsure, say N.
>>   
>> +config TEST_HMM
>> +	tristate "Test HMM (Heterogeneous Memory Management)"
>> +	depends on DEVICE_PRIVATE
>> +	select HMM_MIRROR
>> +        select MMU_NOTIFIER
> 
> extra spaces
Will fix in v8.
> In general I wonder if it even makes sense that DEVICE_PRIVATE is user
> selectable?
Should tests enable the feature or the feature enable the test?
IMHO, if the feature is being compiled into the kernel, that should
enable the menu item for the test. If the feature isn't selected,
no need to test it :-)
>> +static int dmirror_fops_open(struct inode *inode, struct file *filp)
>> +{
>> +	struct cdev *cdev = inode->i_cdev;
>> +	struct dmirror *dmirror;
>> +	int ret;
>> +
>> +	/* Mirror this process address space */
>> +	dmirror = kzalloc(sizeof(*dmirror), GFP_KERNEL);
>> +	if (dmirror == NULL)
>> +		return -ENOMEM;
>> +
>> +	dmirror->mdevice = container_of(cdev, struct dmirror_device,
cdevice);
>> +	mutex_init(&dmirror->mutex);
>> +	xa_init(&dmirror->pt);
>> +
>> +	ret = mmu_interval_notifier_insert(&dmirror->notifier,
current->mm,
>> +				0, ULONG_MAX & PAGE_MASK, &dmirror_min_ops);
>> +	if (ret) {
>> +		kfree(dmirror);
>> +		return ret;
>> +	}
>> +
>> +	/* Pairs with the mmdrop() in dmirror_fops_release(). */
>> +	mmgrab(current->mm);
>> +	dmirror->mm = current->mm;
> 
> The notifier holds a mmgrab, no need for another one
OK. I'll replace dmirror->mm with dmirror->notifier.mm.
>> +	/* Only the first open registers the address space. */
>> +	filp->private_data = dmirror;
> 
> Not sure what this comment means
I'll change the comment to:
	/*
          * The first open of the device character file registers the address
          * space of the process doing the open() system call with the device.
          * Subsequent file opens by other processes will have access to the
          * first process' address space.
          */
>> +static inline struct dmirror_device *dmirror_page_to_device(struct
page *page)
>> +
>> +{
>> +	struct dmirror_chunk *devmem;
>> +
>> +	devmem = container_of(page->pgmap, struct dmirror_chunk, pagemap);
>> +	return devmem->mdevice;
>> +}
> 
> extra devmem var is not really needed
I'll change this to:
	return container_of(page->pgmap, struct dmirror_chunk,
			    pagemap)->mdevice;
>> +
>> +static bool dmirror_device_is_mine(struct dmirror_device *mdevice,
>> +				   struct page *page)
>> +{
>> +	if (!is_zone_device_page(page))
>> +		return false;
>> +	return page->pgmap->ops == &dmirror_devmem_ops &&
>> +		dmirror_page_to_device(page) == mdevice;
>> +}
> 
> Use new owner stuff, right? Actually this is redunant now, the check
> should be just WARN_ON pageowner != self owner
I'll clean this up. dmirror_device_is_mine() isn't needed now.
>> +static int dmirror_do_fault(struct dmirror *dmirror, struct hmm_range
*range)
>> +{
>> +	uint64_t *pfns = range->pfns;
>> +	unsigned long pfn;
>> +
>> +	for (pfn = (range->start >> PAGE_SHIFT);
>> +	     pfn < (range->end >> PAGE_SHIFT);
>> +	     pfn++, pfns++) {
>> +		struct page *page;
>> +		void *entry;
>> +
>> +		/*
>> +		 * HMM_PFN_ERROR is returned if it is accessing invalid memory
>> +		 * either because of memory error (hardware detected memory
>> +		 * corruption) or more likely because of truncate on mmap
>> +		 * file.
>> +		 */
>> +		if (*pfns == range->values[HMM_PFN_ERROR])
>> +			return -EFAULT;
> 
> Unless that snapshot is use hmm_range_fault() never returns success
> and sets PFN_ERROR, so this should be a WARN_ON
> 
>> +		if (!(*pfns & range->flags[HMM_PFN_VALID]))
>> +			return -EFAULT;
> 
> Same with valid.
> 
>> +		page = hmm_device_entry_to_page(range, *pfns);
>> +		/* We asked for pages to be populated but check anyway. */
>> +		if (!page)
>> +			return -EFAULT;
> 
> WARN_ON
> 
>> +		if (is_zone_device_page(page)) {
>> +			/*
>> +			 * TODO: need a way to ask HMM to fault foreign zone
>> +			 * device private pages.
>> +			 */
>> +			if (!dmirror_device_is_mine(dmirror->mdevice, page))
>> +				continue;
> 
> Actually re
> 
>> +static bool dmirror_interval_invalidate(struct mmu_interval_notifier
*mni,
>> +				const struct mmu_notifier_range *range,
>> +				unsigned long cur_seq)
>> +{
>> +	struct dmirror *dmirror = container_of(mni, struct dmirror,
notifier);
>> +	struct mm_struct *mm = dmirror->mm;
>> +
>> +	/*
>> +	 * If the process doesn't exist, we don't need to invalidate
the
>> +	 * device page table since the address space will be torn down.
>> +	 */
>> +	if (!mmget_not_zero(mm))
>> +		return true;
> 
> Why? Don't the notifiers provide for this already.
> 
> mmget_not_zero() is required before calling hmm_range_fault() though
This is a workaround for a problem I don't quite understand.
If you change tools/testing/selftests/vm/hmm-tests.c line 868 to
	ASSERT_EQ(ret, -1);
Then the test will abort, core dump, and cause two problems,
1) the migrated page will be faulted back to system memory in order to write
    it to the core dump. This triggers
lockdep_assert_held(&walk.mm->mmap_sem)
    in walk_page_range().
2) Then after a delay, I get:
[  137.852986] rcu: INFO: rcu_sched self-detected stall on CPU
[  137.858594] rcu: 	0-....: (26000 ticks this GP) idle=69e/1/0x4000000000000002
softirq=34555/34555 fqs=6497
[  137.868439] 	(t=26007 jiffies g=14653 q=271)
[  137.872711] NMI backtrace for cpu 0
[  137.876205] CPU: 0 PID: 6228 Comm: hmm-tests Not tainted 5.6.0-rc6+ #2
[  137.882730] Hardware name: System manufacturer System Product Name/SABERTOOTH
X79, BIOS 4302 08/29/2013
[  137.892115] Call Trace:
[  137.894570]  <IRQ>
[  137.896593]  dump_stack+0x97/0xe0
[  137.899920]  nmi_cpu_backtrace.cold+0x14/0x68
[  137.904287]  ? lapic_can_unplug_cpu.cold+0x39/0x39
[  137.909091]  nmi_trigger_cpumask_backtrace+0xf1/0x10e
[  137.914152]  rcu_dump_cpu_stacks+0xe2/0x125
[  137.918348]  rcu_sched_clock_irq.cold+0x393/0x610
[  137.923069]  update_process_times+0x24/0x50
[  137.927263]  tick_sched_handle+0x68/0x90
[  137.931196]  tick_sched_timer+0x38/0xa0
[  137.935037]  __hrtimer_run_queues+0x1f9/0x6c0
[  137.939403]  ? tick_sched_do_timer+0x90/0x90
[  137.943683]  ? enqueue_hrtimer+0x1a0/0x1a0
[  137.947790]  ? recalibrate_cpu_khz+0x10/0x10
[  137.952064]  ? ktime_get_update_offsets_now+0xed/0x1c0
[  137.957209]  hrtimer_interrupt+0x1a5/0x340
[  137.961315]  ? rcu_read_lock_sched_held+0xa1/0xd0
[  137.966038]  smp_apic_timer_interrupt+0xbb/0x320
[  137.970665]  apic_timer_interrupt+0xf/0x20
[  137.974771]  </IRQ>
[  137.976876] RIP: 0010:xas_load+0x7/0x80
[  137.980718] Code: 80 2f 1a 83 c6 05 e9 8d 7b 01 01 e8 3e b1 b1 fe e9 05 ff ff
ff 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 41 56 41 55 41 54 55 <48> 89
fd 53 4c 8d 6d 10 e8 3c fc ff ff 49 89 c4 4c 89 e0 83 e0 03
[  137.999461] RSP: 0018:ffffc900015e77c8 EFLAGS: 00000246 ORIG_RAX:
ffffffffffffff13
[  138.007028] RAX: ffff8886e508c408 RBX: 0000000000000000 RCX: ffffffff82626c89
[  138.014159] RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffffc900015e78a0
[  138.021293] RBP: ffffc900015e78a0 R08: ffffffff811461c4 R09: fffff520002bcf17
[  138.028426] R10: fffff520002bcf16 R11: 0000000000000003 R12: 0000000002606d10
[  138.035557] R13: ffff8886e508c448 R14: 0000000000000031 R15: ffffffffa06546a0
[  138.042701]  ? do_raw_spin_lock+0x104/0x1d0
[  138.046888]  ? xas_store+0x19/0xa60
[  138.050390]  xas_store+0x5b3/0xa60
[  138.053806]  ? register_lock_class+0x860/0x860
[  138.058267]  __xa_erase+0x96/0x110
[  138.061673]  ? xas_store+0xa60/0xa60
[  138.065267]  xa_erase+0x19/0x30
[  138.068418]  dmirror_interval_invalidate+0x7d/0xc0 [test_hmm]
[  138.074174]  __mmu_notifier_release+0x1a6/0x370
[  138.078714]  ? mmu_notifier_unregister+0x1e0/0x1e0
[  138.083520]  ? lock_downgrade+0x380/0x380
[  138.087535]  ? uprobe_clear_state+0x2e/0x150
[  138.091823]  exit_mmap+0x24d/0x2a0
[  138.095229]  ? do_munmap+0x10/0x10
[  138.098635]  ? __x64_sys_io_setup+0x200/0x200
[  138.102995]  ? __mutex_unlock_slowpath+0xb4/0x3f0
[  138.107704]  ? wait_for_completion+0x250/0x250
[  138.112158]  ? lock_downgrade+0x380/0x380
[  138.116176]  ? check_flags.part.0+0x82/0x210
[  138.120463]  mmput+0xb5/0x210
[  138.123444]  do_exit+0x602/0x14c0
[  138.126776]  ? mm_update_next_owner+0x400/0x400
[  138.131329]  do_group_exit+0x8a/0x140
[  138.135006]  get_signal+0x25b/0x1080
[  138.138606]  do_signal+0x8c/0xa90
[  138.141928]  ? _raw_spin_unlock_irq+0x24/0x30
[  138.146292]  ? mark_held_locks+0x24/0x90
[  138.150219]  ? _raw_spin_unlock_irq+0x24/0x30
[  138.154580]  ? lockdep_hardirqs_on+0x190/0x280
[  138.159026]  ? setup_sigcontext+0x260/0x260
[  138.163210]  ? sigprocmask+0x10b/0x150
[  138.166965]  ? __x64_sys_rt_sigsuspend+0xe0/0xe0
[  138.171594]  ? __x64_sys_rt_sigprocmask+0xfb/0x180
[  138.176394]  ? __ia32_compat_sys_rt_sigprocmask+0x190/0x190
[  138.181965]  ? entry_SYSCALL_64_after_hwframe+0x3e/0xbe
[  138.187192]  ? exit_to_usermode_loop+0x60/0x100
[  138.191723]  ? mark_held_locks+0x24/0x90
[  138.195656]  exit_to_usermode_loop+0x85/0x100
[  138.200023]  do_syscall_64+0x20b/0x290
[  138.203782]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  138.208839] RIP: 0033:0x7f2d349f1625
[  138.212420] Code: c2 b8 ea 00 00 00 0f 05 48 3d 00 f0 ff ff 77 3d 41 89 c0 41
ba 08 00 00 00 31 d2 4c 89 ce bf 02 00 00 00 b8 0e 00 00 00 0f 05 <48> 8b
84 24 08 01 00 00 64 48 33 04 25 28 00 00 00 75 24 44 89 c0
[  138.231163] RSP: 002b:00007ffe84228c60 EFLAGS: 00000246 ORIG_RAX:
000000000000000e
[  138.238731] RAX: 0000000000000000 RBX: 00007f2d349ad040 RCX: 00007f2d349f1625
[  138.245862] RDX: 0000000000000000 RSI: 00007ffe84228c60 RDI: 0000000000000002
[  138.252997] RBP: 00007ffe84228ec0 R08: 0000000000000000 R09: 00007ffe84228c60
[  138.260127] R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000401240
[  138.267261] R13: 00007ffe84229190 R14: 0000000000000000 R15: 0000000000000000
[  138.274554] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: {
0-... } 26428 jiffies s: 277 root: 0x1/.
[  138.285167] rcu: blocking rcu_node structures:
[  138.289641] Task dump for CPU 0:
[  138.292890] hmm-tests       R  running task    27560  6228   6211 0x8000400a
[  138.300002] Call Trace:
[  138.302486]  ? check_chain_key+0x1d1/0x2c0
[  138.306627]  ? __lock_acquire+0x61c/0x2820
[  138.310760]  ? match_held_lock+0x1b/0x230
[  138.314800]  ? check_chain_key+0x1d1/0x2c0
[  138.318937]  ? lock_downgrade+0x380/0x380
[  138.323008]  ? lock_acquire+0xff/0x220
[  138.326795]  ? stack_depot_save+0x137/0x450
[  138.331026]  ? _raw_spin_unlock_irqrestore+0x3e/0x50
[  138.336026]  ? mark_held_locks+0x24/0x90
[  138.340012]  ? _raw_spin_unlock_irqrestore+0x3e/0x50
[  138.345022]  ? lockdep_hardirqs_on+0x190/0x280
[  138.349504]  ? stack_depot_save+0x253/0x450
[  138.353731]  ? check_chain_key+0x1d1/0x2c0
[  138.357871]  ? __lock_acquire+0x61c/0x2820
[  138.362033]  ? match_held_lock+0x1b/0x230
[  138.366070]  ? check_chain_key+0x1d1/0x2c0
[  138.370209]  ? mark_lock+0xac/0x9e0
[  138.373734]  ? mark_lock+0xac/0x9e0
[  138.377261]  ? mark_lock+0xac/0x9e0
[  138.380772]  ? mark_held_locks+0x65/0x90
[  138.384730]  ? mark_lock+0xac/0x9e0
[  138.388249]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[  138.392895]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[  138.397542]  ? lockdep_hardirqs_on+0x190/0x280
[  138.402029]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[  138.406676]  ? mark_lock+0xac/0x9e0
[  138.410209]  ? lock_is_held_type+0x110/0x140
[  138.414509]  ? mark_held_locks+0x65/0x90
[  138.418461]  ? match_held_lock+0x1b/0x230
[  138.422500]  ? match_held_lock+0x1b/0x230
[  138.426551]  ? __lock_acquire+0x11c3/0x2820
[  138.430773]  ? xas_load+0x64/0x80
[  138.434126]  ? xas_store+0xac/0xa60
[  138.437652]  ? register_lock_class+0x860/0x860
[  138.442140]  ? lock_downgrade+0x380/0x380
[  138.446193]  ? _raw_spin_lock+0x2c/0x40
[  138.450059]  ? _raw_spin_unlock+0x17/0x30
[  138.454100]  ? xa_erase+0xe/0x30
[  138.457370]  ? dmirror_interval_invalidate+0x7d/0xc0 [test_hmm]
[  138.463325]  ? __mmu_notifier_release+0x1a6/0x370
[  138.468065]  ? mmu_notifier_unregister+0x1e0/0x1e0
[  138.472896]  ? lock_downgrade+0x380/0x380
[  138.476937]  ? uprobe_clear_state+0x2e/0x150
[  138.481252]  ? exit_mmap+0x24d/0x2a0
[  138.484859]  ? do_munmap+0x10/0x10
[  138.488298]  ? __x64_sys_io_setup+0x200/0x200
[  138.492683]  ? __mutex_unlock_slowpath+0xb4/0x3f0
[  138.497418]  ? wait_for_completion+0x250/0x250
[  138.501897]  ? lock_downgrade+0x380/0x380
[  138.505944]  ? check_flags.part.0+0x82/0x210
[  138.510254]  ? mmput+0xb5/0x210
[  138.513435]  ? do_exit+0x602/0x14c0
[  138.516967]  ? mm_update_next_owner+0x400/0x400
[  138.521545]  ? do_group_exit+0x8a/0x140
[  138.525423]  ? get_signal+0x25b/0x1080
[  138.529225]  ? do_signal+0x8c/0xa90
[  138.532755]  ? _raw_spin_unlock_irq+0x24/0x30
[  138.537143]  ? mark_held_locks+0x24/0x90
[  138.541096]  ? _raw_spin_unlock_irq+0x24/0x30
[  138.545492]  ? lockdep_hardirqs_on+0x190/0x280
[  138.549971]  ? setup_sigcontext+0x260/0x260
[  138.554190]  ? sigprocmask+0x10b/0x150
[  138.557969]  ? __x64_sys_rt_sigsuspend+0xe0/0xe0
[  138.562627]  ? __x64_sys_rt_sigprocmask+0xfb/0x180
[  138.567452]  ? __ia32_compat_sys_rt_sigprocmask+0x190/0x190
[  138.573057]  ? entry_SYSCALL_64_after_hwframe+0x3e/0xbe
[  138.578311]  ? exit_to_usermode_loop+0x60/0x100
[  138.582875]  ? mark_held_locks+0x24/0x90
[  138.586837]  ? exit_to_usermode_loop+0x85/0x100
[  138.591400]  ? do_syscall_64+0x20b/0x290
[  138.595360]  ? entry_SYSCALL_64_after_hwframe+0x49/0xbe
./test_hmm.sh: line 58:  6211 Alarm clock             ./hmm-tests

>> +static int dmirror_fault(struct dmirror *dmirror, unsigned long start,
>> +			 unsigned long end, bool write)
>> +{
>> +	struct mm_struct *mm = dmirror->mm;
>> +	unsigned long addr;
>> +	uint64_t pfns[64];
>> +	struct hmm_range range = {
>> +		.notifier = &dmirror->notifier,
>> +		.pfns = pfns,
>> +		.flags = dmirror_hmm_flags,
>> +		.values = dmirror_hmm_values,
>> +		.pfn_shift = DPT_SHIFT,
>> +		.pfn_flags_mask = ~(dmirror_hmm_flags[HMM_PFN_VALID] |
>> +				    dmirror_hmm_flags[HMM_PFN_WRITE]),
>> +		.default_flags = dmirror_hmm_flags[HMM_PFN_VALID] |
>> +				(write ? dmirror_hmm_flags[HMM_PFN_WRITE] : 0),
>> +		.dev_private_owner = dmirror->mdevice,
>> +	};
>> +	int ret = 0;
>> +
>> +	/* Since the mm is for the mirrored process, get a reference first.
*/
>> +	if (!mmget_not_zero(mm))
>> +		return 0;
> 
> Right
> 
>> +	for (addr = start; addr < end; addr = range.end) {
>> +		range.start = addr;
>> +		range.end = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
>> +
>> +		ret = dmirror_range_fault(dmirror, &range);
>> +		if (ret)
>> +			break;
>> +	}
>> +
>> +	mmput(mm);
>> +	return ret;
>> +}
>> +
>> +static int dmirror_do_read(struct dmirror *dmirror, unsigned long
start,
>> +			   unsigned long end, struct dmirror_bounce *bounce)
>> +{
>> +	unsigned long pfn;
>> +	void *ptr;
>> +
>> +	ptr = bounce->ptr + ((start - bounce->addr) & PAGE_MASK);
>> +
>> +	for (pfn = start >> PAGE_SHIFT; pfn < (end >>
PAGE_SHIFT); pfn++) {
>> +		void *entry;
>> +		struct page *page;
>> +		void *tmp;
>> +
>> +		entry = xa_load(&dmirror->pt, pfn);
>> +		page = xa_untag_pointer(entry);
>> +		if (!page)
>> +			return -ENOENT;
>> +
>> +		tmp = kmap(page);
>> +		memcpy(ptr, tmp, PAGE_SIZE);
>> +		kunmap(page);
>> +
>> +		ptr += PAGE_SIZE;
>> +		bounce->cpages++;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int dmirror_read(struct dmirror *dmirror, struct
hmm_dmirror_cmd *cmd)
>> +{
>> +	struct dmirror_bounce bounce;
>> +	unsigned long start, end;
>> +	unsigned long size = cmd->npages << PAGE_SHIFT;
>> +	int ret;
>> +
>> +	start = cmd->addr;
>> +	end = start + size;
>> +	if (end < start)
>> +		return -EINVAL;
>> +
>> +	ret = dmirror_bounce_init(&bounce, start, size);
>> +	if (ret)
>> +		return ret;
>> +
>> +again:
>> +	mutex_lock(&dmirror->mutex);
>> +	ret = dmirror_do_read(dmirror, start, end, &bounce);
>> +	mutex_unlock(&dmirror->mutex);
>> +	if (ret == 0)
>> +		ret = copy_to_user((void __user *)cmd->ptr, bounce.ptr,
>> +					bounce.size);
> 
> Use u64_to_user_ptr() instead of the cast
Will do.
>> +static int dmirror_write(struct dmirror *dmirror, struct
hmm_dmirror_cmd *cmd)
>> +{
>> +	struct dmirror_bounce bounce;
>> +	unsigned long start, end;
>> +	unsigned long size = cmd->npages << PAGE_SHIFT;
>> +	int ret;
>> +
>> +	start = cmd->addr;
>> +	end = start + size;
>> +	if (end < start)
>> +		return -EINVAL;
>> +
>> +	ret = dmirror_bounce_init(&bounce, start, size);
>> +	if (ret)
>> +		return ret;
>> +	ret = copy_from_user(bounce.ptr, (void __user *)cmd->ptr,
>> +				bounce.size);
> 
> ditto
> 
>> +	if (ret)
>> +		return ret;
>> +
>> +again:
>> +	mutex_lock(&dmirror->mutex);
>> +	ret = dmirror_do_write(dmirror, start, end, &bounce);
>> +	mutex_unlock(&dmirror->mutex);
>> +	if (ret == -ENOENT) {
>> +		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
>> +		ret = dmirror_fault(dmirror, start, end, true);
>> +		if (ret == 0) {
>> +			cmd->faults++;
>> +			goto again;
> 
> Use a loop instead of goto?
OK.
> Also I get this:
> 
> lib/test_hmm.c: In function ?dmirror_devmem_fault_alloc_and_copy?:
> lib/test_hmm.c:1041:25: warning: unused variable ?vma? [-Wunused-variable]
>   1041 |  struct vm_area_struct *vma = args->vma;
> 
> But this is a kernel bug, due to alloc_page_vma being a #define not a
> static inline and me having CONFIG_NUMA off in this .config
Fixed.
I'll repost as a proper series shortly.
> Jason
>

On Thu, Mar 19, 2020 at 03:56:50PM -0700, Ralph Campbell
wrote:
> Adding linux-kselftest at vger.kernel.org for the test config question.
> 
> On 3/19/20 11:17 AM, Jason Gunthorpe wrote:
> > On Tue, Mar 17, 2020 at 04:14:31PM -0700, Ralph Campbell wrote:
> > > 
> > > On 3/17/20 5:59 AM, Christoph Hellwig wrote:
> > > > On Tue, Mar 17, 2020 at 09:47:55AM -0300, Jason Gunthorpe
wrote:
> > > > > I've been using v7 of Ralph's tester and it is
working well - it has
> > > > > DEVICE_PRIVATE support so I think it can test this flow
too. Ralph are
> > > > > you able?
> > > > > 
> > > > > This hunk seems trivial enough to me, can we include it
now?
> > > > 
> > > > I can send a separate patch for it once the tester covers
it.  I don't
> > > > want to add it to the original patch as it is a significant
behavior
> > > > change compared to the existing code.
> > > > 
> > > 
> > > Attached is an updated version of my HMM tests based on
linux-5.6.0-rc6.
> > > I ran this OK with Jason's 8+1 HMM patches, Christoph's
1-5 misc HMM clean ups,
> > > and Christoph's 1-4 device private page changes applied.
> > 
> > I'd like to get this to mergable, it looks pretty good now, but I
have
> > no idea about selftests - and I'm struggling to even compile the
tools
> > dir
> > 
> > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > > index 69def4a9df00..4d22ce7879a7 100644
> > > +++ b/lib/Kconfig.debug
> > > @@ -2162,6 +2162,18 @@ config TEST_MEMINIT
> > >   	  If unsure, say N.
> > > +config TEST_HMM
> > > +	tristate "Test HMM (Heterogeneous Memory Management)"
> > > +	depends on DEVICE_PRIVATE
> > > +	select HMM_MIRROR
> > > +        select MMU_NOTIFIER
> > 
> > extra spaces
> 
> Will fix in v8.
> 
> > In general I wonder if it even makes sense that DEVICE_PRIVATE is user
> > selectable?
> 
> Should tests enable the feature or the feature enable the test?
> IMHO, if the feature is being compiled into the kernel, that should
> enable the menu item for the test. If the feature isn't selected,
> no need to test it :-)
I ment if DEVICE_PRIVATE should be a user selectable option at all, or
should it be turned on when a driver like nouveau is selected.

Is there some downside to enabling DEVICE_PRIVATE?
> > The notifier holds a mmgrab, no need for another one
> 
> OK. I'll replace dmirror->mm with dmirror->notifier.mm.
Right that is good too
> > > +	filp->private_data = dmirror;
> > 
> > Not sure what this comment means
> 
> I'll change the comment to:
> 	  /*
>          * The first open of the device character file registers the
address
>          * space of the process doing the open() system call with the
device.
>          * Subsequent file opens by other processes will have access to the
>          * first process' address space.
>          */
How does this happen? The function looks like it always does the same thing
> > > +static bool dmirror_interval_invalidate(struct
mmu_interval_notifier *mni,
> > > +				const struct mmu_notifier_range *range,
> > > +				unsigned long cur_seq)
> > > +{
> > > +	struct dmirror *dmirror = container_of(mni, struct dmirror,
notifier);
> > > +	struct mm_struct *mm = dmirror->mm;
> > > +
> > > +	/*
> > > +	 * If the process doesn't exist, we don't need to
invalidate the
> > > +	 * device page table since the address space will be torn down.
> > > +	 */
> > > +	if (!mmget_not_zero(mm))
> > > +		return true;
> > 
> > Why? Don't the notifiers provide for this already.
> > 
> > mmget_not_zero() is required before calling hmm_range_fault() though
Oh... This is the invalidate_all path during invalidation

IMHO you should test the invalidation reason in the range to exclude
this.

But xa_erase looks totally safe so there should be no reason to do
that.
> This is a workaround for a problem I don't quite understand.
> If you change tools/testing/selftests/vm/hmm-tests.c line 868 to
> 	ASSERT_EQ(ret, -1);
> Then the test will abort, core dump, and cause two problems,
> 1) the migrated page will be faulted back to system memory in order to
write
>    it to the core dump. This triggers
lockdep_assert_held(&walk.mm->mmap_sem)
>    in walk_page_range().
Has the migration stuff become entangled with the xarray?
> [  137.980718] Code: 80 2f 1a 83 c6 05 e9 8d 7b 01 01 e8 3e b1 b1 fe e9 05
ff ff ff 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 41 56 41 55 41 54 55
<48> 89 fd 53 4c 8d 6d 10 e8 3c fc ff ff 49 89 c4 4c 89 e0 83 e0 03
> [  137.999461] RSP: 0018:ffffc900015e77c8 EFLAGS: 00000246 ORIG_RAX:
ffffffffffffff13
> [  138.007028] RAX: ffff8886e508c408 RBX: 0000000000000000 RCX:
ffffffff82626c89
> [  138.014159] RDX: dffffc0000000000 RSI: 0000000000000000 RDI:
ffffc900015e78a0
> [  138.021293] RBP: ffffc900015e78a0 R08: ffffffff811461c4 R09:
fffff520002bcf17
> [  138.028426] R10: fffff520002bcf16 R11: 0000000000000003 R12:
0000000002606d10
> [  138.035557] R13: ffff8886e508c448 R14: 0000000000000031 R15:
ffffffffa06546a0
> [  138.042701]  ? do_raw_spin_lock+0x104/0x1d0
> [  138.046888]  ? xas_store+0x19/0xa60
> [  138.050390]  xas_store+0x5b3/0xa60
> [  138.053806]  ? register_lock_class+0x860/0x860
> [  138.058267]  __xa_erase+0x96/0x110
> [  138.061673]  ? xas_store+0xa60/0xa60
> [  138.065267]  xa_erase+0x19/0x30
oh, it is doing this:

static void mn_itree_release(struct mmu_notifier_subscriptions *subscriptions,
                             struct mm_struct *mm)
{
        struct mmu_notifier_range range = {
                .flags = MMU_NOTIFIER_RANGE_BLOCKABLE,
                .event = MMU_NOTIFY_RELEASE,
                .mm = mm,
                .start = 0,
                .end = ULONG_MAX,
        };

ie it is sitting doing a huge number of xa_erases, I suppose. Probably
in normal exit the notifier is removed before the mm is destroyed.

The xa_erase needs to be a bit smarter to jump over gaps in the tree
perhaps some

xa_for_each()
   xa_erase()

pattern?
> > Also I get this:
> > 
> > lib/test_hmm.c: In function ?dmirror_devmem_fault_alloc_and_copy?:
> > lib/test_hmm.c:1041:25: warning: unused variable ?vma?
[-Wunused-variable]
> >   1041 |  struct vm_area_struct *vma = args->vma;
> > 
> > But this is a kernel bug, due to alloc_page_vma being a #define not a
> > static inline and me having CONFIG_NUMA off in this .config
> 
> Fixed.
in gfp.h?

Jason

On Thu, Mar 19, 2020 at 09:03:45PM -0300, Jason Gunthorpe
wrote:
> > Should tests enable the feature or the feature enable the test?
> > IMHO, if the feature is being compiled into the kernel, that should
> > enable the menu item for the test. If the feature isn't selected,
> > no need to test it :-)
> 
> I ment if DEVICE_PRIVATE should be a user selectable option at all, or
> should it be turned on when a driver like nouveau is selected.
I don't think it should be user selectable.  This is an implementation
detail users can't know about.
> Is there some downside to enabling DEVICE_PRIVATE?
The option itself adds a little more code to the core kernel, and
introduces a few additional branches in core mm code.

But more importantly it pulls in the whole pgmap infrastructure.