[PATCH] KVM: nVMX: fix MWAIT emulation for guests

From: Wanpeng Li
Date: Thu May 04 2017 - 05:37:58 EST

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

The kvm-unit-tests/vmx.flat fails against instruction(mwait) intercept test.

Test suite: instruction intercept
Unhandled exception 13 #GP at ip 0000000000402397
error_code=0000 rflags=00010012 cs=00000008
rax=0000000000000000 rcx=0000000004006172 rdx=0000000000402397 rbx=000000000041427d
rbp=0000000007ff8fdf rsi=0000000000000000 rdi=0000000000000004
r8=000000000000000a r9=00000000000003f8 r10=0000000000000000 r11=0000000000000000
r12=0000000000000000 r13=0000000000000000 r14=0000000000000000 r15=0000000000000000
cr0=0000000080010031 cr2=0000000000000000 cr3=0000000007fff000 cr4=0000000000002020
STACK: @402397 401102 400459

This testcase will run mwait instruction unconditional in L2 w/o check mwait
cpuid. The vmlauch/vmresume emulation will merge L0's requirements and L1's
requests, kvm-unit-tests doesn't set MWAIT/MONITOR EXITING bits for vmcs12.
w/o commit 668fffa3f838 ("kvm: better MWAIT emulation for guests"), the
MWAIT/MONITOR EXITING bits in vmcs02 will be set since it is set in vmcs01
though not in vmcs12. However, w/ the commit the bits will not be set in vmcs02
since the bits are both not set in vmcs01(if kvm_mwait_in_guest() returns true)
and vmcs12.

L2 should not occupy all the cpu time on L0 when L2 is idle, this patch fix it
by unconditional set MWAIT/MONITOR EXTING bits against vmcs02.

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Alexander Graf <agraf@xxxxxxx>
Cc: "Gabriel L. Somlo" <gsomlo@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
arch/x86/kvm/vmx.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 29940b6..104a0c6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10098,6 +10098,13 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
exec_control &= ~CPU_BASED_USE_IO_BITMAPS;

+ /*
+ * L2 should not occupy all the cpu time on L0 when L2
+ * is idle, exit every time.
+ */
+ exec_control |= CPU_BASED_MWAIT_EXITING |
vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, exec_control);

/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the