linux-kernel - Re: [RFC PATCH 0/2] iommu/s390: Fix iommu-groups and add sysfs support

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Message-ID: <20170427210325.GE1332@8bytes.org>
Date:   Thu, 27 Apr 2017 23:03:25 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:     Sebastian Ott <sebott@...ux.vnet.ibm.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] iommu/s390: Fix iommu-groups and add sysfs
 support

Hi Gerald,

thanks for your reply. I have some more questions, please see below.

On Thu, Apr 27, 2017 at 08:10:18PM +0200, Gerald Schaefer wrote:

> Well, there is a separate zpci_dev for each pci_dev on s390,
> and each of those has its own separate dma-table (thus not shared).

Is that true for all functions of a PCIe card, so does every function of
a device has its own zpci_dev structure and thus its own DMA-table?

My assumption came from the fact that the zpci_dev is read from
pci_dev->sysdata, which is propagated there from the pci_bridge
through the pci_root_bus structures.

> Given this "separate zpci_dev for each pci_dev" situation, I don't
> see what this update actually changes, compared to the previous code,
> see also my comments to that patch.

The add_device call-back is invoked for every function of a pci-device,
because each function gets its own pci_dev structure. Also we usually
group all functions of a PCI-device together into one iommu-group,
because we don't trust that the device isolates its functions from each
other.

Regards,

	Joerg