thr3ads.net - Linux Virtualization - [PATCH] KVM: Add Kconfig option to signal cross-endian guests [Jul 2015]

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Laurent Vivier

2015-Jul-09 09:48 UTC

[PATCH] KVM: Add Kconfig option to signal cross-endian guests

On 09/07/2015 09:49, Thomas Huth wrote:> The option for supporting cross-endianness legacy guests in
> the vhost and tun code should only be available on systems
> that support cross-endian guests.
I'm sure I misunderstand something, but what happens if we use QEMU with
TCG instead of KVM, i.e. a big endian powerpc kernel guest on x86_64
little endian host ?
Do you forbid the use of vhost in this case ?
> Signed-off-by: Thomas Huth <thuth at redhat.com>
> ---
>  arch/arm/kvm/Kconfig     | 1 +
>  arch/arm64/kvm/Kconfig   | 1 +
>  arch/powerpc/kvm/Kconfig | 1 +
>  drivers/net/Kconfig      | 1 +
>  drivers/vhost/Kconfig    | 1 +
>  virt/kvm/Kconfig         | 3 +++
>  6 files changed, 8 insertions(+)
> 
> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
> index bfb915d..9d8f363 100644
> --- a/arch/arm/kvm/Kconfig
> +++ b/arch/arm/kvm/Kconfig
> @@ -31,6 +31,7 @@ config KVM
>  	select KVM_VFIO
>  	select HAVE_KVM_EVENTFD
>  	select HAVE_KVM_IRQFD
> +	select KVM_CROSS_ENDIAN_GUESTS
>  	depends on ARM_VIRT_EXT && ARM_LPAE && ARM_ARCH_TIMER
>  	---help---
>  	  Support hosting virtualized guest machines.
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index bfffe8f..9af39fe 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -31,6 +31,7 @@ config KVM
>  	select KVM_VFIO
>  	select HAVE_KVM_EVENTFD
>  	select HAVE_KVM_IRQFD
> +	select KVM_CROSS_ENDIAN_GUESTS
>  	---help---
>  	  Support hosting virtualized guest machines.
>  
> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> index 3caec2c..e028710 100644
> --- a/arch/powerpc/kvm/Kconfig
> +++ b/arch/powerpc/kvm/Kconfig
> @@ -79,6 +79,7 @@ config KVM_BOOK3S_64_HV
>  	select KVM_BOOK3S_HV_POSSIBLE
>  	select MMU_NOTIFIER
>  	select CMA
> +	select KVM_CROSS_ENDIAN_GUESTS
>  	---help---
>  	  Support running unmodified book3s_64 guest kernels in
>  	  virtual machines on POWER7 and PPC970 processors that have
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index c18f9e6..0c4ce47 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -261,6 +261,7 @@ config TUN
>  config TUN_VNET_CROSS_LE
>  	bool "Support for cross-endian vnet headers on little-endian
kernels"
>  	default n
> +	depends on KVM_CROSS_ENDIAN_GUESTS
>  	---help---
>  	  This option allows TUN/TAP and MACVTAP device drivers in a
>  	  little-endian kernel to parse vnet headers that come from a
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 533eaf0..4d8ae6b 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -35,6 +35,7 @@ config VHOST
>  
>  config VHOST_CROSS_ENDIAN_LEGACY
>  	bool "Cross-endian support for vhost"
> +	depends on KVM_CROSS_ENDIAN_GUESTS
>  	default n
>  	---help---
>  	  This option allows vhost to support guests with a different byte
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index e2c876d..cc7b28a 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -47,3 +47,6 @@ config KVM_GENERIC_DIRTYLOG_READ_PROTECT
>  config KVM_COMPAT
>         def_bool y
>         depends on COMPAT && !S390
> +
> +config KVM_CROSS_ENDIAN_GUESTS
> +       bool
>

Paolo Bonzini

2015-Jul-09 12:57 UTC

head link

[PATCH] KVM: Add Kconfig option to signal cross-endian guests

On 09/07/2015 11:48, Laurent Vivier wrote:> 
> 
> On 09/07/2015 09:49, Thomas Huth wrote:
>> The option for supporting cross-endianness legacy guests in
>> the vhost and tun code should only be available on systems
>> that support cross-endian guests.
> 
> I'm sure I misunderstand something, but what happens if we use QEMU
with
> TCG instead of KVM, i.e. a big endian powerpc kernel guest on x86_64
> little endian host ?
TCG does not yet support irqfd/ioeventfd, so it cannot be used with vhost.

Paolo
> Do you forbid the use of vhost in this case ?
> 
>> Signed-off-by: Thomas Huth <thuth at redhat.com>
>> ---
>>  arch/arm/kvm/Kconfig     | 1 +
>>  arch/arm64/kvm/Kconfig   | 1 +
>>  arch/powerpc/kvm/Kconfig | 1 +
>>  drivers/net/Kconfig      | 1 +
>>  drivers/vhost/Kconfig    | 1 +
>>  virt/kvm/Kconfig         | 3 +++
>>  6 files changed, 8 insertions(+)
>>
>> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
>> index bfb915d..9d8f363 100644
>> --- a/arch/arm/kvm/Kconfig
>> +++ b/arch/arm/kvm/Kconfig
>> @@ -31,6 +31,7 @@ config KVM
>>  	select KVM_VFIO
>>  	select HAVE_KVM_EVENTFD
>>  	select HAVE_KVM_IRQFD
>> +	select KVM_CROSS_ENDIAN_GUESTS
>>  	depends on ARM_VIRT_EXT && ARM_LPAE && ARM_ARCH_TIMER
>>  	---help---
>>  	  Support hosting virtualized guest machines.
>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
>> index bfffe8f..9af39fe 100644
>> --- a/arch/arm64/kvm/Kconfig
>> +++ b/arch/arm64/kvm/Kconfig
>> @@ -31,6 +31,7 @@ config KVM
>>  	select KVM_VFIO
>>  	select HAVE_KVM_EVENTFD
>>  	select HAVE_KVM_IRQFD
>> +	select KVM_CROSS_ENDIAN_GUESTS
>>  	---help---
>>  	  Support hosting virtualized guest machines.
>>  
>> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
>> index 3caec2c..e028710 100644
>> --- a/arch/powerpc/kvm/Kconfig
>> +++ b/arch/powerpc/kvm/Kconfig
>> @@ -79,6 +79,7 @@ config KVM_BOOK3S_64_HV
>>  	select KVM_BOOK3S_HV_POSSIBLE
>>  	select MMU_NOTIFIER
>>  	select CMA
>> +	select KVM_CROSS_ENDIAN_GUESTS
>>  	---help---
>>  	  Support running unmodified book3s_64 guest kernels in
>>  	  virtual machines on POWER7 and PPC970 processors that have
>> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
>> index c18f9e6..0c4ce47 100644
>> --- a/drivers/net/Kconfig
>> +++ b/drivers/net/Kconfig
>> @@ -261,6 +261,7 @@ config TUN
>>  config TUN_VNET_CROSS_LE
>>  	bool "Support for cross-endian vnet headers on little-endian
kernels"
>>  	default n
>> +	depends on KVM_CROSS_ENDIAN_GUESTS
>>  	---help---
>>  	  This option allows TUN/TAP and MACVTAP device drivers in a
>>  	  little-endian kernel to parse vnet headers that come from a
>> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
>> index 533eaf0..4d8ae6b 100644
>> --- a/drivers/vhost/Kconfig
>> +++ b/drivers/vhost/Kconfig
>> @@ -35,6 +35,7 @@ config VHOST
>>  
>>  config VHOST_CROSS_ENDIAN_LEGACY
>>  	bool "Cross-endian support for vhost"
>> +	depends on KVM_CROSS_ENDIAN_GUESTS
>>  	default n
>>  	---help---
>>  	  This option allows vhost to support guests with a different byte
>> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
>> index e2c876d..cc7b28a 100644
>> --- a/virt/kvm/Kconfig
>> +++ b/virt/kvm/Kconfig
>> @@ -47,3 +47,6 @@ config KVM_GENERIC_DIRTYLOG_READ_PROTECT
>>  config KVM_COMPAT
>>         def_bool y
>>         depends on COMPAT && !S390
>> +
>> +config KVM_CROSS_ENDIAN_GUESTS
>> +       bool
>>

Michael S. Tsirkin

2015-Jul-09 13:07 UTC

head link

[PATCH] KVM: Add Kconfig option to signal cross-endian guests

On Thu, Jul 09, 2015 at 02:57:33PM +0200, Paolo Bonzini
wrote:> 
> 
> On 09/07/2015 11:48, Laurent Vivier wrote:
> > 
> > 
> > On 09/07/2015 09:49, Thomas Huth wrote:
> >> The option for supporting cross-endianness legacy guests in
> >> the vhost and tun code should only be available on systems
> >> that support cross-endian guests.
> > 
> > I'm sure I misunderstand something, but what happens if we use
QEMU with
> > TCG instead of KVM, i.e. a big endian powerpc kernel guest on x86_64
> > little endian host ?
> 
> TCG does not yet support irqfd/ioeventfd, so it cannot be used with vhost.
> 
> Paolo
vhost does not require irqfd anymore.  I think ioeventfd actually works
fine though I didn't try, it would be easy to support.

> > Do you forbid the use of vhost in this case ?
> > 
> >> Signed-off-by: Thomas Huth <thuth at redhat.com>
> >> ---
> >>  arch/arm/kvm/Kconfig     | 1 +
> >>  arch/arm64/kvm/Kconfig   | 1 +
> >>  arch/powerpc/kvm/Kconfig | 1 +
> >>  drivers/net/Kconfig      | 1 +
> >>  drivers/vhost/Kconfig    | 1 +
> >>  virt/kvm/Kconfig         | 3 +++
> >>  6 files changed, 8 insertions(+)
> >>
> >> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
> >> index bfb915d..9d8f363 100644
> >> --- a/arch/arm/kvm/Kconfig
> >> +++ b/arch/arm/kvm/Kconfig
> >> @@ -31,6 +31,7 @@ config KVM
> >>  	select KVM_VFIO
> >>  	select HAVE_KVM_EVENTFD
> >>  	select HAVE_KVM_IRQFD
> >> +	select KVM_CROSS_ENDIAN_GUESTS
> >>  	depends on ARM_VIRT_EXT && ARM_LPAE &&
ARM_ARCH_TIMER
> >>  	---help---
> >>  	  Support hosting virtualized guest machines.
> >> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> >> index bfffe8f..9af39fe 100644
> >> --- a/arch/arm64/kvm/Kconfig
> >> +++ b/arch/arm64/kvm/Kconfig
> >> @@ -31,6 +31,7 @@ config KVM
> >>  	select KVM_VFIO
> >>  	select HAVE_KVM_EVENTFD
> >>  	select HAVE_KVM_IRQFD
> >> +	select KVM_CROSS_ENDIAN_GUESTS
> >>  	---help---
> >>  	  Support hosting virtualized guest machines.
> >>  
> >> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> >> index 3caec2c..e028710 100644
> >> --- a/arch/powerpc/kvm/Kconfig
> >> +++ b/arch/powerpc/kvm/Kconfig
> >> @@ -79,6 +79,7 @@ config KVM_BOOK3S_64_HV
> >>  	select KVM_BOOK3S_HV_POSSIBLE
> >>  	select MMU_NOTIFIER
> >>  	select CMA
> >> +	select KVM_CROSS_ENDIAN_GUESTS
> >>  	---help---
> >>  	  Support running unmodified book3s_64 guest kernels in
> >>  	  virtual machines on POWER7 and PPC970 processors that have
> >> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> >> index c18f9e6..0c4ce47 100644
> >> --- a/drivers/net/Kconfig
> >> +++ b/drivers/net/Kconfig
> >> @@ -261,6 +261,7 @@ config TUN
> >>  config TUN_VNET_CROSS_LE
> >>  	bool "Support for cross-endian vnet headers on
little-endian kernels"
> >>  	default n
> >> +	depends on KVM_CROSS_ENDIAN_GUESTS
> >>  	---help---
> >>  	  This option allows TUN/TAP and MACVTAP device drivers in a
> >>  	  little-endian kernel to parse vnet headers that come from a
> >> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> >> index 533eaf0..4d8ae6b 100644
> >> --- a/drivers/vhost/Kconfig
> >> +++ b/drivers/vhost/Kconfig
> >> @@ -35,6 +35,7 @@ config VHOST
> >>  
> >>  config VHOST_CROSS_ENDIAN_LEGACY
> >>  	bool "Cross-endian support for vhost"
> >> +	depends on KVM_CROSS_ENDIAN_GUESTS
> >>  	default n
> >>  	---help---
> >>  	  This option allows vhost to support guests with a different
byte
> >> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> >> index e2c876d..cc7b28a 100644
> >> --- a/virt/kvm/Kconfig
> >> +++ b/virt/kvm/Kconfig
> >> @@ -47,3 +47,6 @@ config KVM_GENERIC_DIRTYLOG_READ_PROTECT
> >>  config KVM_COMPAT
> >>         def_bool y
> >>         depends on COMPAT && !S390
> >> +
> >> +config KVM_CROSS_ENDIAN_GUESTS
> >> +       bool
> >>

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