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

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Message-ID: <4EF0516F.2030102@siemens.com>
Date:	Tue, 20 Dec 2011 10:12:15 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Sasha Levin <levinsasha928@...il.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 2011-12-20 10:08, Sasha Levin wrote:
> 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?

This iommu-less mode used to "work" for older qemu-kvm version, and I
think it should still do. Though it makes no sense, I fully agree.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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