Re: [Xen-devel] [PATCH V2 2/2] x86/altp2m: Fixed domain crash with INVALID_ALTP2M EPTP index

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.06.18 at 14:40, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> Crash:
>> 
>> (XEN) [ 1924.367273] altp2m_vcpu_initialise()
>> (XEN) [ 1924.367277] altp2m_vcpu_reset()
>> (XEN) [ 1924.367278] 1 altp2m_vcpu_update_p2m()
>> (XEN) [ 1924.367279] vmx_vcpu_update_eptp()
>> (XEN) [ 1924.367318] HVMOP_altp2m_vcpu_enable_notify
>> (XEN) [ 1924.367321] vmx_vcpu_update_vmfunc_ve(0),
>> v->arch.hvm_vmx.secondary_exec_control: 0x1054eb
>> (XEN) [ 1924.367326] exit vmx_vcpu_update_vmfunc_ve(0),
>> v->arch.hvm_vmx.secondary_exec_control: 0x1474eb
>> (XEN) [ 1924.367344] Xen BUG at vmx.c:3407
> 
> Actually I think this shows us the problem: 65535 (INVALID_ALTP2M) is a
> stale value from a previous good run. But the EPTP_INDEX value is
> ignored unless SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS is set. So at the
> crash point, SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS just got set, the
> "live" index is 0, and the stale INVALID_ALTP2M value is being read from
> the previous run (and compared to 0 and MAX_ALTP2M).

So perhaps the writing of EPTP_INDEX should be done earlier?

Jan



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