linux-kernel - Re: [PATCH] vfio/noiommu: Don't use iommu

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Message-ID: <56A56A48.9090405@ozlabs.ru>
Date:	Mon, 25 Jan 2016 11:20:24 +1100
From:	Alexey Kardashevskiy <aik@...abs.ru>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	anatoly.burakov@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, ferruh.yigit@...el.com, dev@...k.org
Subject: Re: [PATCH] vfio/noiommu: Don't use iommu_present() to track fake
 groups

On 01/23/2016 04:23 AM, Alex Williamson wrote:
> Using iommu_present() to determine whether an IOMMU group is real or
> fake has some problems.  First, apparently Power systems don't
> register an IOMMU on the device bus, so the groups and containers get
> marked as noiommu and then won't bind to their actual IOMMU driver.
> Second, I expect we'll run into the same issue as we try to support
> vGPUs through vfio, since they're likely to emulate this behavior of
> creating an IOMMU group on a virtual device and then providing a vfio
> IOMMU backend tailored to the sort of isolation they provide, which
> won't necessarily be fully compatible with the IOMMU API.
>
> The solution here is to use the existing iommudata interface to IOMMU
> groups, which allows us to easily identify the fake groups we've
> created for noiommu purposes.  The iommudata we set is purely
> arbitrary since we're only comparing the address, so we use the
> address of the noiommu switch itself.
>
> Reported-by: Alexey Kardashevskiy <aik@...abs.ru>
> Fixes: 03a76b60f8ba ("vfio: Include No-IOMMU mode")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>



Reviewed-by: Alexey Kardashevskiy <aik@...abs.ru>
Tested-by: Alexey Kardashevskiy <aik@...abs.ru>

Thanks!


-- 
Alexey