linux-kernel - Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling

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Date:	Wed, 19 Jun 2013 11:58:50 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	"kvm@...r.kernel.org mailing list" <kvm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	kvm-ppc@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 3/4] KVM: PPC: Add support for IOMMU in-kernel handling


On 19.06.2013, at 06:59, Benjamin Herrenschmidt wrote:

> On Wed, 2013-06-19 at 13:05 +0930, Rusty Russell wrote:
>> symbol_get() won't try to load a module; it'll just fail.  This is what
>> you want, since they must have vfio in the kernel to get a valid fd...
> 
> Ok, cool. I suppose what we want here Alexey is slightly higher level,
> something like:
> 
> 	vfio_validate_iommu_id(file, iommu_id)
> 
> Which verifies that the file that was passed in is allowed to use
> that iommu_id.
> 
> That's a simple and flexible interface (ie, it will work even if we
> support multiple iommu IDs in the future for a vfio, for example
> for DDW windows etc...), the logic to know about the ID remains
> in qemu, this is strictly a validation call.
> 
> That way we also don't have to expose the containing vfio struct etc...
> just that simple function.
> 
> Alex, any objection ?

Which Alex? :)

I think validate works, it keeps iteration logic out of the kernel which is a good thing. There still needs to be an interface for getting the iommu id in VFIO, but I suppose that one's for the other Alex and Jörg to comment on.

> 
> Do we need to make it a get/put interface instead ?
> 
> 	vfio_validate_and_use_iommu(file, iommu_id);
> 
> 	vfio_release_iommu(file, iommu_id);
> 
> To ensure that the resource remains owned by the process until KVM
> is closed as well ?
> 
> Or do we want to register with VFIO with a callback so that VFIO can
> call us if it needs us to give it up ?

Can't we just register a handler on the fd and get notified when it closes? Can you kill VFIO access without closing the fd?


Alex

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