On Thu, Jul 09, 2015 at 02:57:33PM +0200, Paolo Bonzini wrote:

On 09/07/2015 11:48, Laurent Vivier wrote:

quoted

On 09/07/2015 09:49, Thomas Huth wrote:

quoted

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.

quoted

Do you forbid the use of vhost in this case ?

quoted

Signed-off-by: Thomas Huth <redacted>
---
 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