Re: [Xen-devel] [PATCH RFC 03/12] xen/x86: allow the emulated APICs to be enbled for the hardware domain

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Fri, Jul 29, 2016 at 06:50:48PM +0100, Andrew Cooper wrote:
> On 29/07/16 17:28, Roger Pau Monne wrote:
> >          if ( is_hardware_domain(d) )
> > -            config->emulation_flags |= XEN_X86_EMU_PIT;
> > -        if ( config->emulation_flags != 0 &&
> > -             (config->emulation_flags !=
> > -              (is_hvm_domain(d) ? XEN_X86_EMU_ALL : XEN_X86_EMU_PIT)) )
> > +            emflags |= XEN_X86_EMU_PIT;
> > +
> > +        if ( (is_hardware_domain(d) ?
> > +              (is_hvm_domain(d) && emflags !=
> > +              (XEN_X86_EMU_PIT|XEN_X86_EMU_LAPIC|XEN_X86_EMU_IOAPIC)) :
> > +              (emflags && (is_hvm_domain(d) ? (emflags != XEN_X86_EMU_ALL) 
> > :
> > +                                              (emflags != 
> > XEN_X86_EMU_PIT)))) )
> 
> This is getting very complicated.
> 
> It is rather important (security wise) and not a hotpath.  Could I
> please request that you move this logic to a helper such as:
> 
> static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
> 
> and make this more readable.  Any decent compiler will inline and
> simplify it appropriately.

Thanks, I've now moved it to a helper as suggested:

static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
{

    if ( is_hvm_domain(d) )
    {
        if ( is_hardware_domain(d) &&
             emflags != (XEN_X86_EMU_PIT|XEN_X86_EMU_LAPIC|XEN_X86_EMU_IOAPIC))
            return false;
        if ( !is_hardware_domain(d) &&
             emflags != XEN_X86_EMU_ALL && emflags != 0 )
            return false;
    }
    else
    {
        /* PV or classic PVH. */
        if ( is_hardware_domain(d) && emflags != XEN_X86_EMU_PIT )
            return false;
        if ( !is_hardware_domain(d) && emflags != 0 )
            return false;
    }
    return true;
}

Roger.

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