linux-kernel - Re: [RFC PATCH 11/34] iommu: Split off default domain allocation from group assignment

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Date:   Mon, 13 Apr 2020 22:10:50 +0000
From:   "Derrick, Jonathan" <jonathan.derrick@...el.com>
To:     "heiko@...ech.de" <heiko@...ech.de>,
        "kgene@...nel.org" <kgene@...nel.org>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
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        "agross@...nel.org" <agross@...nel.org>
CC:     "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
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        <linux-samsung-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [RFC PATCH 11/34] iommu: Split off default domain allocation
 from group assignment

Hi Joerg,

On Tue, 2020-04-07 at 20:37 +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> When a bus is initialized with iommu-ops, all devices on the bus are
> scanned and iommu-groups are allocated for them, and each groups will
> also get a default domain allocated.
> 
> Until now this happened as soon as the group was created and the first
> device added to it. When other devices with different default domain
> requirements were added to the group later on, the default domain was
> re-allocated, if possible.
> 
> This resulted in some back and forth and unnecessary allocations, so
> change the flow to defer default domain allocation until all devices
> have been added to their respective IOMMU groups.
> 
> The default domains are allocated for newly allocated groups after
> each device on the bus is handled and was probed by the IOMMU driver.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
> ---
[snip]


I had to add the following for initial VMD support. The new PCIe domain
added on VMD endpoint probe didn't have the dev_iommu member set on the
VMD subdevices, which I'm guessing is due to probe_iommu_group already
having been run on the VMD endpoint's group prior to those subdevices
being added.

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 8a5e1ac328dd..ac1e4fb9bf48 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1577,6 +1577,9 @@ static int iommu_bus_notifier(struct notifier_block *nb,
        if (action == BUS_NOTIFY_ADD_DEVICE) {
                int ret;
 
+               if (!dev_iommu_get(dev))
+                       return -ENOMEM;
+
                ret = iommu_probe_device(dev);
                return (ret) ? NOTIFY_DONE : NOTIFY_OK;
        } else if (action == BUS_NOTIFY_REMOVED_DEVICE) {