From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
To: Jan Beulich <jbeulich@suse.com>,
"sstabellini@kernel.org" <sstabellini@kernel.org>,
"julien@xen.org" <julien@xen.org>
Cc: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
Artem Mygaiev <Artem_Mygaiev@epam.com>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"george.dunlap@citrix.com" <george.dunlap@citrix.com>,
"paul@xen.org" <paul@xen.org>,
Bertrand Marquis <bertrand.marquis@arm.com>,
Rahul Singh <rahul.singh@arm.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"roger.pau@citrix.com" <roger.pau@citrix.com>,
Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
Subject: Re: [PATCH v4 02/11] vpci: cancel pending map/unmap on vpci removal
Date: Tue, 16 Nov 2021 14:37:56 +0000 [thread overview]
Message-ID: <5c670333-42be-b080-8c7a-a166d681800b@epam.com> (raw)
In-Reply-To: <55a95ff3-6717-780b-25f9-c43728b6270b@epam.com>
On 16.11.21 16:24, Oleksandr Andrushchenko wrote:
>
> On 16.11.21 16:12, Jan Beulich wrote:
>> On 16.11.2021 14:41, Oleksandr Andrushchenko wrote:
>>> On 16.11.21 10:23, Oleksandr Andrushchenko wrote:
>>>> On 16.11.21 10:01, Jan Beulich wrote:
>>>>> On 16.11.2021 08:32, Oleksandr Andrushchenko wrote:
>>>>>> On 15.11.21 18:56, Jan Beulich wrote:
>>>>>>> On 05.11.2021 07:56, Oleksandr Andrushchenko wrote:
>>>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>>>>>>
>>>>>>>> When a vPCI is removed for a PCI device it is possible that we have
>>>>>>>> scheduled a delayed work for map/unmap operations for that device.
>>>>>>>> For example, the following scenario can illustrate the problem:
>>>>>>>>
>>>>>>>> pci_physdev_op
>>>>>>>> pci_add_device
>>>>>>>> init_bars -> modify_bars -> defer_map -> raise_softirq(SCHEDULE_SOFTIRQ)
>>>>>>>> iommu_add_device <- FAILS
>>>>>>>> vpci_remove_device -> xfree(pdev->vpci)
>>>>>>>>
>>>>>>>> leave_hypervisor_to_guest
>>>>>>>> vpci_process_pending: v->vpci.mem != NULL; v->vpci.pdev->vpci == NULL
>>>>>>>>
>>>>>>>> For the hardware domain we continue execution as the worse that
>>>>>>>> could happen is that MMIO mappings are left in place when the
>>>>>>>> device has been deassigned
>>>>>>> Is continuing safe in this case? I.e. isn't there the risk of a NULL
>>>>>>> deref?
>>>>>> I think it is safe to continue
>>>>> And why do you think so? I.e. why is there no race for Dom0 when there
>>>>> is one for DomU?
>>>> Well, then we need to use a lock to synchronize the two.
>>>> I guess this needs to be pci devs lock unfortunately
>>> The parties involved in deferred work and its cancellation:
>>>
>>> MMIO trap -> vpci_write -> vpci_cmd_write -> modify_bars -> defer_map
>>>
>>> Arm: leave_hypervisor_to_guest -> check_for_vcpu_work -> vpci_process_pending
>>>
>>> x86: two places -> hvm_do_resume -> vpci_process_pending
>>>
>>> So, both defer_map and vpci_process_pending need to be synchronized with
>>> pcidevs_{lock|unlock).
>> If I was an Arm maintainer, I'm afraid I would object to the pcidevs lock
>> getting used in leave_hypervisor_to_guest.
> I do agree this is really not good, but it seems I am limited in choices.
> @Stefano, @Julien, do you see any better way of doing that?
>
> We were thinking about introducing a dedicated lock for vpci [1],
> but finally decided to use pcidevs_lock for now
Or even better and simpler: we just use pdev->vpci->lock to
protect vpci_process_pending vs MMIO trap handlers which already
use it.
>> Jan
>>
> [1] https://lore.kernel.org/all/afe47397-a792-6b0c-0a89-b47c523e50d9@epam.com/
next prev parent reply other threads:[~2021-11-16 14:38 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-05 6:56 [PATCH v4 00/11] PCI devices passthrough on Arm, part 3 Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 01/11] vpci: fix function attributes for vpci_process_pending Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 02/11] vpci: cancel pending map/unmap on vpci removal Oleksandr Andrushchenko
2021-11-15 16:56 ` Jan Beulich
2021-11-16 7:32 ` Oleksandr Andrushchenko
2021-11-16 8:01 ` Jan Beulich
2021-11-16 8:23 ` Oleksandr Andrushchenko
2021-11-16 11:38 ` Jan Beulich
2021-11-16 13:27 ` Oleksandr Andrushchenko
2021-11-16 14:11 ` Jan Beulich
2021-11-16 13:41 ` Oleksandr Andrushchenko
2021-11-16 14:12 ` Jan Beulich
2021-11-16 14:24 ` Oleksandr Andrushchenko
2021-11-16 14:37 ` Oleksandr Andrushchenko [this message]
2021-11-16 16:09 ` Jan Beulich
2021-11-16 18:02 ` Julien Grall
2021-11-18 12:57 ` Oleksandr Andrushchenko
2021-11-17 8:28 ` Jan Beulich
2021-11-18 7:49 ` Oleksandr Andrushchenko
2021-11-18 8:36 ` Jan Beulich
2021-11-18 8:54 ` Oleksandr Andrushchenko
2021-11-18 9:15 ` Jan Beulich
2021-11-18 9:32 ` Oleksandr Andrushchenko
2021-11-18 13:25 ` Jan Beulich
2021-11-18 13:48 ` Oleksandr Andrushchenko
2021-11-18 14:04 ` Roger Pau Monné
2021-11-18 14:14 ` Oleksandr Andrushchenko
2021-11-18 14:35 ` Jan Beulich
2021-11-18 15:11 ` Oleksandr Andrushchenko
2021-11-18 15:16 ` Jan Beulich
2021-11-18 15:21 ` Oleksandr Andrushchenko
2021-11-18 15:41 ` Jan Beulich
2021-11-18 15:46 ` Oleksandr Andrushchenko
2021-11-18 15:53 ` Jan Beulich
2021-11-19 12:34 ` Oleksandr Andrushchenko
2021-11-19 13:00 ` Jan Beulich
2021-11-19 13:16 ` Oleksandr Andrushchenko
2021-11-19 13:25 ` Jan Beulich
2021-11-19 13:34 ` Oleksandr Andrushchenko
2021-11-22 14:21 ` Oleksandr Andrushchenko
2021-11-22 14:37 ` Jan Beulich
2021-11-22 14:45 ` Oleksandr Andrushchenko
2021-11-22 14:57 ` Jan Beulich
2021-11-22 15:02 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 03/11] vpci: make vpci registers removal a dedicated function Oleksandr Andrushchenko
2021-11-15 16:57 ` Jan Beulich
2021-11-16 8:02 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 04/11] vpci: add hooks for PCI device assign/de-assign Oleksandr Andrushchenko
2021-11-15 17:06 ` Jan Beulich
2021-11-16 9:38 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 05/11] vpci/header: implement guest BAR register handlers Oleksandr Andrushchenko
2021-11-19 11:58 ` Jan Beulich
2021-11-19 12:10 ` Oleksandr Andrushchenko
2021-11-19 12:37 ` Jan Beulich
2021-11-19 12:46 ` Oleksandr Andrushchenko
2021-11-19 12:49 ` Jan Beulich
2021-11-19 12:54 ` Oleksandr Andrushchenko
2021-11-19 13:02 ` Jan Beulich
2021-11-19 13:17 ` Oleksandr Andrushchenko
2021-11-23 15:14 ` Oleksandr Andrushchenko
2021-11-24 12:32 ` Roger Pau Monné
2021-11-24 12:36 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 06/11] vpci/header: handle p2m range sets per BAR Oleksandr Andrushchenko
2021-11-19 12:05 ` Jan Beulich
2021-11-19 12:13 ` Oleksandr Andrushchenko
2021-11-19 12:45 ` Jan Beulich
2021-11-19 12:50 ` Oleksandr Andrushchenko
2021-11-19 13:06 ` Jan Beulich
2021-11-19 13:19 ` Oleksandr Andrushchenko
2021-11-19 13:29 ` Jan Beulich
2021-11-19 13:38 ` Oleksandr Andrushchenko
2021-11-19 13:16 ` Jan Beulich
2021-11-19 13:41 ` Oleksandr Andrushchenko
2021-11-19 13:57 ` Jan Beulich
2021-11-19 14:09 ` Oleksandr Andrushchenko
2021-11-22 8:24 ` Jan Beulich
2021-11-22 8:31 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 07/11] vpci/header: program p2m with guest BAR view Oleksandr Andrushchenko
2021-11-19 12:33 ` Jan Beulich
2021-11-19 12:44 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 08/11] vpci/header: emulate PCI_COMMAND register for guests Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 09/11] vpci/header: reset the command register when adding devices Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 10/11] vpci: add initial support for virtual PCI bus topology Oleksandr Andrushchenko
2021-11-18 16:45 ` Jan Beulich
2021-11-24 11:28 ` Oleksandr Andrushchenko
2021-11-24 12:36 ` Roger Pau Monné
2021-11-24 12:43 ` Oleksandr Andrushchenko
2021-11-05 6:56 ` [PATCH v4 11/11] xen/arm: translate virtual PCI bus topology for guests Oleksandr Andrushchenko
2021-11-08 11:10 ` Jan Beulich
2021-11-08 11:16 ` Oleksandr Andrushchenko
2021-11-08 14:23 ` Roger Pau Monné
2021-11-08 15:28 ` Oleksandr Andrushchenko
2021-11-24 11:31 ` Oleksandr Andrushchenko
2021-11-19 13:56 ` [PATCH v4 00/11] PCI devices passthrough on Arm, part 3 Jan Beulich
2021-11-19 14:06 ` Oleksandr Andrushchenko
2021-11-19 14:23 ` Roger Pau Monné
2021-11-19 14:26 ` Oleksandr Andrushchenko
2021-11-20 9:47 ` Roger Pau Monné
2021-11-22 8:22 ` Jan Beulich
2021-11-22 8:34 ` Oleksandr Andrushchenko
2021-11-22 8:44 ` Jan Beulich
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