Bug 45931

Created attachment 77661 [details]
xl-dmesg-in-L1-Xen.log

Hi folks,
I did some basic testing on nested virtualization on Intel x86-64 platform.
Will KVM support Xen as L1 guest in nested virtualization ?

When I tried "Xen on KVM" mode, I found VMX can't be initialized in L1 Xen hypervisor.
I tried both "-cpu host" and "-cpu qemu64,+vmx" parameters in qemu-kvm command line.
-------some log in 'xl dmesg' command line in L1 Xen ---
(XEN) VMX: CPU0 has insufficent CPU-Based Exec Control (b299868c but requires min 2299968c)
(XEN) VMX: CPU0 has insufficent VMExit Control (00000200 but requires min 00008200)
(XEN) VMX: failed to initialise.
------more details in the attached "xl-dmesg-L1.log"----
In Xen source code, I found the following related to the mentioned error.
"xen-unstable.hg/xen/include/asm-x86/hvm/vmx/vmcs.h"
#define CPU_BASED_RDTSC_EXITING               0x00001000
#define VM_EXIT_ACK_INTR_ON_EXIT        0x00008000


----
Avi confirmed there're two issues, and fixed 1st one (RDTSC) by the following patch.

All processors that support VMX have that feature, and guests (Xen) depend on
it.  As we already implement it, advertize it to the guest.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/kvm/vmx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cc8ad98..8092f25 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1990,7 +1990,7 @@ static __init void nested_vmx_setup_ctls_msrs(void)
 #endif
 		CPU_BASED_MOV_DR_EXITING | CPU_BASED_UNCOND_IO_EXITING |
 		CPU_BASED_USE_IO_BITMAPS | CPU_BASED_MONITOR_EXITING |
-		CPU_BASED_RDPMC_EXITING |
+		CPU_BASED_RDPMC_EXITING | CPU_BASED_RDTSC_EXITING |
 		CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
 	/*
 	 * We can allow some features even when not supported by the