Re: Remapping BOs and registers post BAR movements [was - Re: Question about supporting AMD eGPU hot plug case]

* Re: Remapping BOs and registers post BAR movements [was - Re: Question about supporting AMD eGPU hot plug case]
       [not found]   ` <5c2b2379-9961-c6f6-b343-b874cc22260f@amd.com>
@ 2021-03-02 17:48     ` Andrey Grodzovsky
  2021-03-03 16:05       ` Andrey Grodzovsky
  0 siblings, 1 reply; 4+ messages in thread
From: Andrey Grodzovsky @ 2021-03-02 17:48 UTC (permalink / raw)
  To: Christian König, Bjorn Helgaas
  Cc: Alexander.Deucher, Sergei Miroshnichenko, linux-pci

Adding PCI mailing list per Bjorn's advise (sorry, skipped the address 
last time).

On 2021-03-02 12:22 p.m., Christian König wrote:
> Hi Andrey,
> 
>> Can you elaborate more why you need such a lock on a global level and not
>> enough per driver (per device more specifically) local lock acquired in
>> rescan_preapare (before BARs shuffling starts) and released in 
>> rescan_done
>> (after BARs shuffling done) ? 
> 
> because this adds inter device dependencies.
> 
> E.g. when we have device A, B and C and each is taking it's own lock we 
> end up with 3 locks.
> 
> If those device have inter dependencies on their own, for example 
> because of DMA-buf we will end up in quite a locking mess.
> 
> Apart from that if we don't always keep the order A, B, C but instead 
> end up with A, C, B lockdep will certainly start to complain.
> 
> Regards,
> Christian.

But as far as I understand those locks are agnostic to each other - each 
lock is taken only by it's respective device and not by others. So I 
don't see deadlock danger here but, I do suspect lockdep might throw a 
false warning...

Andrey

> 
> Am 02.03.21 um 18:16 schrieb Andrey Grodzovsky:
>> Per Bjorn's advise adding PCI mailing list.
>>
>> Christian, please reply on top of this mail and not on top the 
>> earlier, original one.
>>
>> Andrey
>>
>> On 2021-03-02 11:49 a.m., Bjorn Helgaas wrote:
>>> Please add linux-pci@vger.kernel.org to the cc list.  There's a lot of
>>> useful context in this thread and it needs to be archived.
>>> On Tue, Mar 02, 2021 at 11:37:25AM -0500, Andrey Grodzovsky wrote:
>>>> Adding Sergei and Bjorn since you are suggesting some PCI related 
>>>> changes.
>>>>
>>>> On 2021-03-02 6:28 a.m., Christian König wrote:
>>>>> Yeah, I'm thinking about that as well for quite a while now.
>>>>>
>>>>> I'm not 100% sure what Sergei does in his patch set will work for 
>>>>> us. He
>>>>> basically tells the driver to stop any processing then shuffle around
>>>>> the BARs and then tells him to start again.
>>>>>
>>>>> Because of the necessity to reprogram bridges there isn't much 
>>>>> other way
>>>>> how to do this, but we would need something like taking a lock,
>>>>> returning and dropping the lock later on. If you do this for multiple
>>>>> drivers at the same time this results in a locking nightmare.
>>>>>
>>>>> What we need instead is a upper level PCI layer rw-lock which we can
>>>>> take on the read side in the driver, similar to our internal reset 
>>>>> lock.
>>>>
>>>>
>>>> Can you elaborate more why you need such a lock on a global level 
>>>> and not
>>>> enough per driver (per device more specifically) local lock acquired in
>>>> rescan_preapare (before BARs shuffling starts) and released in 
>>>> rescan_done
>>>> (after BARs shuffling done) ?
>>>>
>>>> Andrey
>>>>
>>>>
>>>>>
>>>>> Wiring up changing the mapping is the smaller problem in that picture.
>>>>>
>>>>> Christian.
>>>>>
>>>>> Am 01.03.21 um 22:14 schrieb Andrey Grodzovsky:
>>>>>> Hi, I started looking into actual implementation for this, as
>>>>>> reference point I am using Sege's NVME implementations (see 
>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FYADRO-KNS%2Flinux%2Fcommit%2F58c375df086502538706ee23e8ef7c8bb5a4178f&amp;data=04%7C01%7Candrey.grodzovsky%40amd.com%7C44bc68a68feb4b71836c08d8dd9b306a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637503005898302093%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=nuTptAjGewG2T7tXOQr2h%2Bdr42lyg3m1%2Bfv0mJzd8tw%3D&amp;reserved=0) 
>>>>>>
>>>>>> and our own amdgpu_device_resize_fb_bar. Our use case being more
>>>>>> complicated then NVME's arises some questions or thoughts:
>>>>>>
>>>>>> Before the PCI core will move the BARs (VRAM and registers) we have
>>>>>> to stop the HW and SW and then unmap all MMIO mapped entitles in the
>>>>>> driver. This includes, registers of all types and  VRAM placed BOs
>>>>>> with CPU visibility. My concern is how to prevent accesses to all
>>>>>> MMIO ranges between iounmap in rescan_preapare and ioremap in
>>>>>> rescan_done. For register accesses we are again back to same issue
>>>>>> we had with device unplug and GPU reset we are discussing with Denis
>>>>>> now. So here at least as first solution just to confirm the feature
>>>>>> works I can introduce low level (in register accessors) RW locking
>>>>>> to avoid access until all register access driver pointers are
>>>>>> remapped post BARs move. What more concerns me is how to - In
>>>>>> rescan_preapare: collect all CPU accessible BOs placed in VRAM (i
>>>>>> can use amdgpu specific list like I currently use for device
>>>>>> unplug), lock them to prevent any further use of them, unpin them
>>>>>> (and unmap). In rescan_preapare: remap them back and unlock them for
>>>>>> further use. Also, there is a difference between kernel BOs where
>>>>>> indeed iounmap, ioremap should be enough and user space mapped BOs
>>>>>> where it seems like in hot unplug, we need in rescan_preapare to
>>>>>> only unamp them, in between drop new page faults with VM_FAULT_RETRY
>>>>>> and post rescan_done allow page faults to go through to refill all
>>>>>> the user page tables with updated MMIO addresses.
>>>>>>
>>>>>> Let me know your thoughts.
>>>>>>
>>>>>> Andrey
>>>>>>
>>>>>> On 2021-02-26 4:03 p.m., Andrey Grodzovsky wrote:
>>>>>>>
>>>>>>> On 2021-02-26 1:44 a.m., Sergei Miroshnichenko wrote:
>>>>>>>> On Thu, 2021-02-25 at 13:28 -0500, Andrey Grodzovsky wrote:
>>>>>>>>> On 2021-02-25 2:00 a.m., Sergei Miroshnichenko wrote:
>>>>>>>>>> On Wed, 2021-02-24 at 17:51 -0500, Andrey Grodzovsky wrote:
>>>>>>>>>>> On 2021-02-24 1:23 p.m., Sergei Miroshnichenko wrote:
>>>>>>>>>>>> ...
>>>>>>>>>>> Are you saying that even without hot-plugging, while both nvme
>>>>>>>>>>> and
>>>>>>>>>>> AMD
>>>>>>>>>>> card are present
>>>>>>>>>>> right from boot, you still get BARs moving and MMIO ranges
>>>>>>>>>>> reassigned
>>>>>>>>>>> for NVME BARs
>>>>>>>>>>> just because amdgpu driver will start resize of AMD card BARs 
>>>>>>>>>>> and
>>>>>>>>>>> this
>>>>>>>>>>> will trigger NVMEs BARs move to
>>>>>>>>>>> allow AMD card BARs to cover full range of VIDEO RAM ?
>>>>>>>>>> Yes. Unconditionally, because it is unknown beforehand if NVMe's
>>>>>>>>>> BAR
>>>>>>>>>> movement will help. In this particular case BAR movement is not
>>>>>>>>>> needed,
>>>>>>>>>> but is done anyway.
>>>>>>>>>>
>>>>>>>>>> BARs are not moved one by one, but the kernel releases all the
>>>>>>>>>> releasable ones, and then recalculates a new BAR layout to fit 
>>>>>>>>>> them
>>>>>>>>>> all. Kernel's algorithm is different from BIOS's, so NVME has
>>>>>>>>>> appeared
>>>>>>>>>> at a new place.
>>>>>>>>>>
>>>>>>>>>> This is triggered by following:
>>>>>>>>>> - at boot, if BIOS had assigned not every BAR;
>>>>>>>>>> - during pci_resize_resource();
>>>>>>>>>> - during pci_rescan_bus() -- after a pciehp event or a manual via
>>>>>>>>>> sysfs.
>>>>>>>>> By manual via sysfs you mean something like this - 'echo 1 >
>>>>>>>>> /sys/bus/pci/drivers/amdgpu/0000\:0c\:00.0/remove && echo 1 >
>>>>>>>>> /sys/bus/pci/rescan ' ? I am looking into how most reliably 
>>>>>>>>> trigger
>>>>>>>>> PCI
>>>>>>>>> code to call my callbacks even without having external PCI cage 
>>>>>>>>> for
>>>>>>>>> GPU
>>>>>>>>> (will take me some time to get it).
>>>>>>>> Yeah, this is our way to go when a device can't be physically 
>>>>>>>> removed
>>>>>>>> or unpowered remotely. With just a bit shorter path:
>>>>>>>>
>>>>>>>>     sudo sh -c 'echo 1 > 
>>>>>>>> /sys/bus/pci/devices/0000\:0c\:00.0/remove'
>>>>>>>>     sudo sh -c 'echo 1 > /sys/bus/pci/rescan'
>>>>>>>>
>>>>>>>> Or, just a second command (rescan) is enough: a BAR movement 
>>>>>>>> attempt
>>>>>>>> will be triggered even if there were no changes in PCI topology.
>>>>>>>>
>>>>>>>> Serge
>>>>>>>
>>>>>>>
>>>>>>> Ok, able to trigger stub callbacks call after doing rescan from
>>>>>>> sysfs. Also I see BARs movement
>>>>>>>
>>>>>>> [ 1860.968036] amdgpu 0000:09:00.0: BAR 0: assigned [mem
>>>>>>> 0xc0000000-0xcfffffff 64bit pref]
>>>>>>> [ 1860.968050] amdgpu 0000:09:00.0: BAR 0 updated: 0xe0000000 ->
>>>>>>> 0xc0000000
>>>>>>> [ 1860.968054] amdgpu 0000:09:00.0: BAR 2: assigned [mem
>>>>>>> 0xd0000000-0xd01fffff 64bit pref]
>>>>>>> [ 1860.968068] amdgpu 0000:09:00.0: BAR 2 updated: 0xf0000000 ->
>>>>>>> 0xd0000000
>>>>>>> [ 1860.968071] amdgpu 0000:09:00.0: BAR 5: assigned [mem
>>>>>>> 0xf0100000-0xf013ffff]
>>>>>>> [ 1860.968078] amdgpu 0000:09:00.0: BAR 5 updated: 0xfce00000 ->
>>>>>>> 0xf0100000
>>>>>>>
>>>>>>> As expected, after the move the device becomes unresponsive as
>>>>>>> unmap/ioremap wasn't done.
>>>>>>>
>>>>>>> Andrey
>>>>>>>
>>>>>
> 

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