Re: [Xen-devel] Xen 4.6.1 crash with altp2m enabledbydefault

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.08.16 at 11:48, <Kevin.Mayer@xxxxxxxx> wrote:
> vmx_vmenter_helper is not part of the call stack. The address is simply the 
> location of the ud2 to which the 
> __vmwrite(HOST_CR0, v->arch.hvm_vmx.host_cr0);
> In
> static void vmx_fpu_leave(struct vcpu *v)
> jumps.
> There are two vmwrites in vmx_vcpu_update_eptp (called by 
> altp2m_vcpu_destroy):
> __vmwrite(EPT_POINTER, ept_get_eptp(ept));
> __vmwrite(EPTP_INDEX, vcpu_altp2m(v).p2midx);
> 
> And four in vmx_vcpu_update_vmfunc_ve (also called by altp2m_vcpu_destroy)
> __vmwrite(VM_FUNCTION_CONTROL, VMX_VMFUNC_EPTP_SWITCHING);
> __vmwrite(EPTP_LIST_ADDR, virt_to_maddr(d->arch.altp2m_eptp));
> __vmwrite(VIRT_EXCEPTION_INFO, mfn_x(mfn) << PAGE_SHIFT);
> __vmwrite(SECONDARY_VM_EXEC_CONTROL,  
> v->arch.hvm_vmx.secondary_exec_control);
> 
> After the altp2m-part hvm_vcpu_destroy also calls nestedhvm_vcpu_destroy(v), 
> but this code path is executed unconditionally so I assume that the error 
> lies somewhere in the altp2m_vcpu_destroy(v).
> 
> What exactly are the vmx_vmcs_enter / exit required for? I often see the 
> vmx_vmcs_enter; __vmwrite; vmx_vmcs_exit combination. Need the __vmwrites be 
> guarded by an enter / exit ( which Is not the case in the static void 
> vmx_fpu_leave(struct vcpu *v) )?

On code paths where the correct VMCS may not be the current one
it is necessary to frame vmread / vmwrite accordingly.

> Is it possible that the 
> altp2m_vcpu_destroy->vmx_vcpu_update_eptp->vmx_vmcs_exit->vmx_clear_vmcs 
> invalidates the vmcs for the current vcpu?

I certainly can't exclude this possibility.

Jan


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