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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.06.18 at 10:52, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -3592,7 +3592,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
>              }
>          }
>  
> -        if ( idx != vcpu_altp2m(v).p2midx )
> +        if ( idx != INVALID_ALTP2M && idx != vcpu_altp2m(v).p2midx )
>          {
>              BUG_ON(idx >= MAX_ALTP2M);

In the code immediately ahead of this there is an INVALID_ALTP2M check
already (in the else branch). If the __vmread() can legitimately produce
this value, why would the domain be crashed when getting back
INVALID_ALTP2M in the other case? I think the correctness of your change
can only be judged once both code paths behave consistently.

Jan



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