linux-kernel - RE: [PATCH v2 06/12] iommu/vt-d: Acquiring lock in domain ID allocation helpers

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Date:   Tue, 14 Jun 2022 06:52:22 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason Gunthorpe" <jgg@...dia.com>
CC:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 06/12] iommu/vt-d: Acquiring lock in domain ID
 allocation helpers

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 14, 2022 10:52 AM
> 
> The iommu->lock is used to protect the per-IOMMU domain ID resource.
> Moving the lock into the ID alloc/free helpers makes the code more
> compact. At the same time, the device_domain_lock is irrelevant to
> the domain ID resource, remove its assertion as well.
> 
> On the other hand, the iommu->lock is never used in interrupt context,
> there's no need to use the irqsave variant of the spinlock calls.

I still prefer to separating reduction of lock ranges from changing irqsave.
Locking is tricky. From bisect p.o.v. it will be a lot easier if we just change
one logic in one patch.