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RE: [PATCH 1/8] IOMMU/x86: drop locking from quarantine_init() hooks
- To: "Beulich, Jan" <JBeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
- Date: Wed, 20 Apr 2022 06:22:42 +0000
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- Cc: Paul Durrant <paul@xxxxxxx>, "Cooper, Andrew" <andrew.cooper3@xxxxxxxxxx>, Pau Monné, Roger <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 20 Apr 2022 06:22:54 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHYTYeTB5xLKnU08E+muTG4n+sN9qz4W6FQ
- Thread-topic: [PATCH 1/8] IOMMU/x86: drop locking from quarantine_init() hooks
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Monday, April 11, 2022 5:36 PM
>
> Prior extension of these functions to enable per-device quarantine page
> tables already didn't add more locking there, but merely left in place
> what had been there before. But really locking is unnecessary here:
> We're running with pcidevs_lock held (i.e. multiple invocations of the
> same function [or their teardown equivalents] are impossible, and hence
> there are no "local" races), while all consuming of the data being
> populated here can't race anyway due to happening sequentially
> afterwards. See also the comment in struct arch_pci_dev.
Better add some explanation (as you explained in other replies)
why above rationale around pcidevs_lock leads to the drop of
a different lock (mapping_lock).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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