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Re: [PATCH v8 02/13] vpci: use per-domain PCI lock to protect vpci structure
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 21 Jul 2023 10:48:27 +0200
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- Cc: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 21 Jul 2023 08:48:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.07.2023 09:43, Roger Pau Monné wrote:
> On Fri, Jul 21, 2023 at 08:02:33AM +0200, Jan Beulich wrote:
>> On 20.07.2023 18:14, Roger Pau Monné wrote:
>>> Strictly speaking however the init
>>> handlers don't require the lock in write mode unless we use such
>>> locking to get exclusive access to all the devices assigned to the
>>> domain BARs array for modify_bars().
>>
>> Aiui in the present model modify_bars() has to use the vpci lock for
>> protection.
>
> But the current protection is insufficient, as we only hold the vpci
> lock of the current device, but we don't hold the vpci lock of the
> other devices when we iterate over in order to find overlapping bars
> (or else it wold be an ABBA deadlock situation).
>
> So my suggestion (which can be done later) is to take the newly
> introduced per-domain rwlock in exclusive mode for modify_bars() in
> order to assert there are no changes to the other devices vpci bar
> fields.
I think this makes sense, just that it doesn't belong in this patch.
Jan
>> Therefore imo in any of the init functions the assertions
>> should either express the real requirements of those functions, or be
>> omitted on the basis that they're all called out of add-handlers
>> anyway.
>
> I'm happy to omit for the time being. Iff we agree that modify_bars()
> requires the rwlock in exclusive mode then we could add the assertion
> there, but not in the init functions themselves.
>
> Thanks, Roger.
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