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

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

> (XEN) [ 1923.964832] altp2m_vcpu_initialise()
> (XEN) [ 1923.964836] altp2m_vcpu_reset()
> (XEN) [ 1923.964837] 1 altp2m_vcpu_update_p2m()
> (XEN) [ 1923.964838] vmx_vcpu_update_eptp()
> (XEN) [ 1923.964876] HVMOP_altp2m_vcpu_enable_notify
> (XEN) [ 1923.964878] vmx_vcpu_update_vmfunc_ve(0),
> v->arch.hvm_vmx.secondary_exec_control: 0x1054eb
> (XEN) [ 1923.964880] exit vmx_vcpu_update_vmfunc_ve(0),
> v->arch.hvm_vmx.secondary_exec_control: 0x1474eb
> (XEN) [ 1923.964986] altp2m_vcpu_destroy()
> (XEN) [ 1923.964987] altp2m_vcpu_reset()
> (XEN) [ 1923.964988] 2 altp2m_vcpu_update_p2m()
> (XEN) [ 1923.964989] vmx_vcpu_update_eptp()
> (XEN) [ 1923.964991] __vmwrite(EPTP_INDEX, 65535)
> (XEN) [ 1923.964992] vmx_vcpu_update_vmfunc_ve(0),
> v->arch.hvm_vmx.secondary_exec_control: 0x1474eb
> (XEN) [ 1923.964993] exit vmx_vcpu_update_vmfunc_ve(0),
> v->arch.hvm_vmx.secondary_exec_control: 0x1054eb
> 
> 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).


Thanks,
Razvan

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