linux-kernel - Re: [PATCH 1/2] kvm: Remove ability to assign a device without iommu support

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Date:	Tue, 20 Dec 2011 11:08:48 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	"avi@...hat.com" <avi@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kvm: Remove ability to assign a device without
 iommu support

On Tue, 2011-12-20 at 10:03 +0100, Jan Kiszka wrote:
> On 2011-12-20 09:49, Sasha Levin wrote:
> > On Mon, 2011-12-19 at 20:19 -0700, Alex Williamson wrote:
> >> This option has no users and it exposes a security hole that we
> >> can allow devices to be assigned without iommu protection.  Make
> >> KVM_DEV_ASSIGN_ENABLE_IOMMU a mandatory option.
> >>
> >> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> >> ---
> >>
> >>  virt/kvm/assigned-dev.c |   18 +++++++++---------
> >>  1 files changed, 9 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> >> index 3ad0925..a251a28 100644
> >> --- a/virt/kvm/assigned-dev.c
> >> +++ b/virt/kvm/assigned-dev.c
> >> @@ -487,6 +487,9 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
> >>  	struct kvm_assigned_dev_kernel *match;
> >>  	struct pci_dev *dev;
> >>  
> >> +	if (!(assigned_dev->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU))
> >> +		return -EINVAL;
> > 
> > Could we just drop KVM_DEV_ASSIGN_ENABLE_IOMMU and do it by default?
> > calling KVM_ASSIGN_PCI_DEVICE without that flag set it pretty
> > meaningless.
> 
> There is that thing called "backward compatibility". :)

Well, Alex suggested skipping deprecation period because there are
currently no users of KVM_ASSIGN_PCI_DEVICE without
KVM_DEV_ASSIGN_ENABLE_IOMMU, so it should be fine to just make it the
default behavior, no?

We can leave KVM_DEV_ASSIGN_ENABLE_IOMMU itself so userspace won't
break, but theres no reason to enforce it being set in the kernel code.

-- 

Sasha.

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