Re: [Xen-devel] [PATCH V14 5/7] xen/arm: Instruction prefetch abort (X) mem_access event handling

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-03-27 at 22:18 +0000, Tamas K Lengyel wrote:

>         
>         >                                        union hsr hsr)
>         >  {
>         > -    register_t addr = READ_SYSREG(FAR_EL2);
>         > -    inject_iabt_exception(regs, addr, hsr.len);
>         > +    struct hsr_iabt iabt = hsr.iabt;
>         > +    int rc;
>         > +    paddr_t gpa;
>         > +    register_t gva = READ_SYSREG(FAR_EL2);
>         > +
>         > +    if ( iabt.s1ptw )
>         > +        gpa = READ_SYSREG(HPFAR_EL2);
>         > +    else
>         
>         
>         Can you not avoid the else case entirely by extending the if to cover
>         the other cases where HPFAR is explicitly valid? I can't be bothered 
> to
>         go look right now but IIRC it included at least stage 2 access
>         permissions related failures, which would cover more xenaccess
>         scenarios, no?
> 
> 
> Depending on the fault cause, we might. For permission faults, HPFAR
> is only valid during s1ptw.. Given that the only check we do is for
> permission faults and that's the only thing that cares about the API
> anyway, we can put this entire block into the switch itself once the
> fault check is already determined to be a permission fault.

According to ARMv8 ARM HPFAR is valid for any of these:
      * A Translation or Access Flag fault on a stage 2 translation.
      * A stage 2 Address Size fault.
      * A fault on the stage 2 translation of an address accessed in a
        stage 1 translation table walk.

I think what you are (correctly) saying is that it omits "a permission
fault on a stage 2 translation", which is one of the cases which can
occur under xenaccess. Which is shame :-(

Ian.



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