Re: [Xen-devel] [PATCH 2/3] xen/p2m: Using INVALID_MFN instead of mfn_valid

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Thursday, August 16, 2012 6:12 PM
> To: Hao, Xudong
> Cc: Zhang, Xiantao; xen-devel@xxxxxxxxxxxxx; tim@xxxxxxx
> Subject: RE: [Xen-devel] [PATCH 2/3] xen/p2m: Using INVALID_MFN instead of
> mfn_valid
> 
> >>> On 16.08.12 at 12:05, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> >>> On 15.08.12 at 08:57, Xudong Hao <xudong.hao@xxxxxxxxx> wrote:
> >> > --- a/xen/arch/x86/mm/p2m-ept.c  Tue Jul 24 17:02:04 2012 +0200
> >> > +++ b/xen/arch/x86/mm/p2m-ept.c  Thu Jul 26 15:40:01 2012 +0800
> >> > @@ -428,7 +428,7 @@ ept_set_entry(struct p2m_domain *p2m, un
> >> >      }
> >> >
> >> >      /* Track the highest gfn for which we have ever had a valid mapping
> */
> >> > -    if ( mfn_valid(mfn_x(mfn)) &&
> >> > +    if ( (mfn_x(mfn) != INVALID_MFN) &&
> >> >           (gfn + (1UL << order) - 1 > p2m->max_mapped_pfn) )
> >> >          p2m->max_mapped_pfn = gfn + (1UL << order) - 1;
> >>
> >> Depending on how the above comment gets addressed (i.e.
> >> whether MMIO MFNs are to be considered here at all), this
> >> might need changing anyway, as this a huge max_mapped_pfn
> >> value likely wouldn't be very useful anymore.
> >
> > Your viewpoint is similar with us. Here max_mapped_pfn value is for memory
> > but not for MMIO. I think this is a simple changes, do you have another
> > suggestion?
> 
> The question is why this needs to be changed at all. If this is
> only about RAM, then mfn_valid() is the right thing to use. If
> this is about MMIO too, then the condition is wrong already
> (since, as we appear to agree, even now there can be MMIO
> above RAM, provided there's little enough RAM).
> 

The original code considered EPT only, now for the device assignment, it need 
to consider MMIO. So how about remove the mfn_valid() here?

> Jan


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