On 08.02.22 15:38, Roger Pau Monné wrote:
> On Tue, Feb 08, 2022 at 11:13:41AM +0000, Oleksandr Andrushchenko wrote:
>>
>> On 08.02.22 12:50, Roger Pau Monné wrote:
>>> On Tue, Feb 08, 2022 at 07:35:34AM +0000, Oleksandr Andrushchenko wrote:
>>>> 5. You name it
>>>> ==============================================================
>>>>
>>>> From all the above I would recommend we go with option 2 which seems to
>>>> reliably
>>>> solve ABBA and does not bring cons of the other approaches.
>>> 6. per-domain rwlock + per-device vpci lock
>>>
>>> Introduce vpci_header_write_lock(start, {end, size}) helper: return
>>> whether a range requires the per-domain lock in write mode. This will
>>> only return true if the range overlaps with the BAR ROM or the command
>>> register.
>>>
>>> In vpci_{read,write}:
>>>
>>> if ( vpci_header_write_lock(...) )
>>> /* Gain exclusive access to all of the domain pdevs vpci. */
>>> write_lock(d->vpci);
>>> else
>>> {
>>> read_lock(d->vpci);
>>> spin_lock(vpci->lock);
>>> }
>>> ...
>>>
>>> The vpci assign/deassign functions would need to be modified to write
>>> lock the per-domain rwlock. The MSI-X table MMIO handler will also
>>> need to read lock the per domain vpci lock.
>> Ok, so it seems you are in favor of this implementation and I have
>> no objection as well. The only limitation we should be aware of is
>> that once a path has acquired the read lock it is not possible to do
>> any write path operations in there.
>> vpci_process_pending will acquire write lock though as it can
>> lead to vpci_remove_device on its error path.
>>
>> So, I am going to implement pdev->vpci->lock + d->vpci_lock
> I think it's the less uncertain option.
>
> As said, if you want to investigate whether you can successfully move
> the checking into vpci_process_pending that would also be fine with
> me, but I cannot assert it's going to be successful. OTOH I think the
> per-domain rwlock + per-device spinlock seems quite likely to solve
> our issues.
Ok, then I'll go with per-domain rwlock + per-device spinlock
and write lock in vpci_write for cmd + ROM. Of course other
places such as vpci_remove_device and vpci_process_pending
will use write lock
>
> Thanks, Roger.
>
Thank you,
Oleksandr
