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Re: [RFC PATCH] pci: introduce per-domain PCI rwlock
- To: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Wed, 12 Jul 2023 11:09:12 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>, Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 12 Jul 2023 11:11:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHZs5ESsjHhLtlMU0qzCbDGds6cO6+0XLQAgABxyYCAAQ0QAIAAE50A
- Thread-topic: [RFC PATCH] pci: introduce per-domain PCI rwlock
Hi Jan, Roger,
Jan Beulich <jbeulich@xxxxxxxx> writes:
> Up front remark: I'm sorry for some possibly unhelpful replies below. I,
> for one, am of the opinion that some of the issues you ask about are to
> be looked into by whoever wants / needs to rework the locking model.
> After all this (likely) is why nobody has dared to make an attempt before
> the need became apparent.
I have no great need desire or need to rework the locking model. I was
perfectly fine with much narrower vpci_lock. As you remember, it is
Roger who suggested to extend this lock to the include the whole PCI
device.
I already tried something like this as part of the another patch series:
"[RFC,01/10] xen: pci: add per-domain pci list lock" [1], with the same
result: it was considered very hard to do this properly, so I dropped
that effort. I am not so familiar with x86-specific code as a whole and
IOMMU drivers in particular to be 100% sure that I am doing correct
changes. Without support from x86 guys I can't do proper patches and
looks like x86 guys are not interested in this. So, this is dead end.
Roger, in [2] I proposed another approach to fix ABBA in modify_bars():
store copy of BARs in the domain structure. Taking into account that my
effort to introduce d->pci_lock basically failed (again), I am proposing
to return back to d->vpci_lock + BARs shadow copy in the domain
struct. What do you think? And you, Jan?
[1]
https://lore.kernel.org/all/20220831141040.13231-2-volodymyr_babchuk@xxxxxxxx/
[2] https://lore.kernel.org/all/87ilbfnqmo.fsf@xxxxxxxx/
--
WBR, Volodymyr
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