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Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings
From: |
Joerg Roedel |
Subject: |
Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings |
Date: |
Sun, 28 Aug 2011 15:56:33 +0200 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Sun, Aug 28, 2011 at 04:14:00PM +0300, Avi Kivity wrote:
> On 08/26/2011 12:24 PM, Roedel, Joerg wrote:
>> The biggest problem with this approach is that it has to happen in the
>> context of the given process. Linux can't really modify an mm which
>> which belong to another context in a safe way.
>>
>
> Is use_mm() insufficient?
Yes, it introduces a set of race conditions when a process that already
has an mm wants to take over another processes mm temporarily (and when
use_mm is modified to actually provide this functionality). It is only
save when used from kernel-thread context.
One example:
Process A Process B Process C
. . .
. <-- takes A->mm .
. and assignes as B->mm .
. . --> Wants to take
. . B->mm, but gets
A->mm now
This can't be secured by a lock, because it introduces potential
A->B<-->B->A lock problem when two processes try to take each others mm.
It could probably be solved by a task->real_mm pointer, havn't thought
about this yet...
Joerg
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, (continued)
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Alex Williamson, 2011/08/22
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Alex Williamson, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Alex Williamson, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/25
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Alexander Graf, 2011/08/25
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, David Gibson, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/26
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Avi Kivity, 2011/08/28
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings,
Joerg Roedel <=
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Avi Kivity, 2011/08/28
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Joerg Roedel, 2011/08/30
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Benjamin Herrenschmidt, 2011/08/22
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Benjamin Herrenschmidt, 2011/08/23
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Roedel, Joerg, 2011/08/24
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, aafabbri, 2011/08/22
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Benjamin Herrenschmidt, 2011/08/22
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, aafabbri, 2011/08/22
- Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings, Benjamin Herrenschmidt, 2011/08/22