linux-kernel - Re: [PATCH v5 02/12] iommu/vt-d: Manage scalalble mode PASID tables

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Date:   Wed, 5 Dec 2018 16:50:12 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 02/12] iommu/vt-d: Manage scalalble mode PASID tables

On Tue, Dec 04, 2018 at 01:58:06PM +0800, Lu Baolu wrote:
> This function is called in an unsleepable context.
> 
> spin_lock(&lock)
> [...]
> if (pasid_table_is_necessary)
> 	allocate_pasid_table(dev)
> [...]
> spin_unlock(&lock)
> 
> We can move it out of the lock range.
> 
> How about
> 
> if (pasid_table_is_necessary)
> 	pasid_table = allocate_pasid_table(dev)
> 
> spin_lock(&lock)
> [...]
> if (pasid_table_is_necessary)
> 	set_up_pasid_table(pasid_table)
> [...]
> spin_unlock(&lock)

Hmm, so when the IOMMU is configured in scalable mode we can just
allocate a pasid-table for the device when we set it up, right?

Scalable mode is a boot-time decision, so we know for sure whether we
need a pasid-table on device-setup time. And the device-setup code it
preemptable, so I think it this allocation should be outside of any
spin-locked section.


	Joerg