Messages in this thread | | | Subject | Re: [PATCH] KVM: nVMX: fix MWAIT emulation for guests | From | Alexander Graf <> | Date | Thu, 4 May 2017 11:43:31 +0200 |
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On 04.05.17 11:37, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > 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 > cr8=0000000000000000 > 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.
I don't understand - why not? If both L0 and L1 hypervisors allow MWAIT execution, why should we stop L2 from executing it?
We don't prevent L2 from running busy loops either, right?
Alex
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