[PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[Paolo Bonzini]

VFIO has proved itself a much better option than KVM's built-in
device assignment.  It is mature, provides better isolation because
it enforces ACS, and even the userspace code is being tested on
a wider variety of hardware these days than the legacy support.

Disable legacy device assignment by default.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/Kconfig | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 413a7bf9efbb..a0f06a5947c5 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -88,13 +88,14 @@ config KVM_MMU_AUDIT
 config KVM_DEVICE_ASSIGNMENT
 	bool "KVM legacy PCI device assignment support"
 	depends on KVM && PCI && IOMMU_API
-	default y
+	default n
 	---help---
 	  Provide support for legacy PCI device assignment through KVM.  The
 	  kernel now also supports a full featured userspace device driver
-	  framework through VFIO, which supersedes much of this support.
+	  framework through VFIO, which supersedes this support and provides
+	  better security.
 
-	  If unsure, say Y.
+	  If unsure, say N.
 
 # OK, it's a little counter-intuitive to do this, but it puts it neatly under
 # the virtualization menu.
-- 
1.8.3.1

Re: [PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[Bandan Das]

Paolo Bonzini <pbonzini@redhat.com> writes:

> VFIO has proved itself a much better option than KVM's built-in
> device assignment.  It is mature, provides better isolation because
> it enforces ACS, and even the userspace code is being tested on
> a wider variety of hardware these days than the legacy support.
>
> Disable legacy device assignment by default.

Shouldn't we mark it as Deprecated then ?

Bandan
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/Kconfig | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 413a7bf9efbb..a0f06a5947c5 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -88,13 +88,14 @@ config KVM_MMU_AUDIT
>  config KVM_DEVICE_ASSIGNMENT
>  	bool "KVM legacy PCI device assignment support"
>  	depends on KVM && PCI && IOMMU_API
> -	default y
> +	default n
>  	---help---
>  	  Provide support for legacy PCI device assignment through KVM.  The
>  	  kernel now also supports a full featured userspace device driver
> -	  framework through VFIO, which supersedes much of this support.
> +	  framework through VFIO, which supersedes this support and provides
> +	  better security.
>  
> -	  If unsure, say Y.
> +	  If unsure, say N.
>  
>  # OK, it's a little counter-intuitive to do this, but it puts it neatly under
>  # the virtualization menu.

Re: [PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[Paolo Bonzini]

On 04/06/2015 16:31, Bandan Das wrote:
> > VFIO has proved itself a much better option than KVM's built-in
> > device assignment.  It is mature, provides better isolation because
> > it enforces ACS, and even the userspace code is being tested on
> > a wider variety of hardware these days than the legacy support.
> >
> > Disable legacy device assignment by default.
>
> Shouldn't we mark it as Deprecated then ?

Yes, good idea!  You mean just " (DEPRECATED)" after the string, right?

Paolo

Re: [PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[Alex Williamson]

On Thu, 2015-06-04 at 16:33 +0200, Paolo Bonzini wrote:
> 
> On 04/06/2015 16:31, Bandan Das wrote:
> > > VFIO has proved itself a much better option than KVM's built-in
> > > device assignment.  It is mature, provides better isolation because
> > > it enforces ACS, and even the userspace code is being tested on
> > > a wider variety of hardware these days than the legacy support.
> > >
> > > Disable legacy device assignment by default.
> >
> > Shouldn't we mark it as Deprecated then ?
> 
> Yes, good idea!  You mean just " (DEPRECATED)" after the string, right?

The ioctls should probably also be listed as deprecated in
Documentation/virtual/kvm/api.txt.  There's also
Documentation/ABI/obsolete if we intend to remove the code eventually.

Re: [PATCH] kvm: x86: default legacy PCI device assignment support to "n"

[Bandan Das]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 04/06/2015 16:31, Bandan Das wrote:
>> > VFIO has proved itself a much better option than KVM's built-in
>> > device assignment.  It is mature, provides better isolation because
>> > it enforces ACS, and even the userspace code is being tested on
>> > a wider variety of hardware these days than the legacy support.
>> >
>> > Disable legacy device assignment by default.
>>
>> Shouldn't we mark it as Deprecated then ?
>
> Yes, good idea!  You mean just " (DEPRECATED)" after the string, right?

Yeah, that is what I meant. The "Help" message does mention VFIO as the
newer option. Sometimes, seeing the word "DEPRECATED" makes one rethink if they
really need to enable it.

> Paolo