Re: [PATCH 7/8] xen/mmu: Introduce IDENTITY_FRAME_BIT

Konrad Rzeszutek Wilk
2011-01-04T16:46:04Z

On Tue, Jan 04, 2011 at 04:26:15PM +0000, Ian Campbell wrote:
> On Thu, 2010-12-30 at 19:48 +0000, Konrad Rzeszutek Wilk wrote:
> > @@ -52,9 +53,12 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)
> >
> > mfn = get_phys_to_machine(pfn);
> >
> > - if (mfn != INVALID_P2M_ENTRY)
> > + if (mfn != INVALID_P2M_ENTRY) {
> > mfn &= ~FOREIGN_FRAME_BIT;
> >
> > + if (mfn & IDENTITY_FRAME_BIT)
> > + mfn &= ~IDENTITY_FRAME_BIT;
> > + }
>
> I don't think the inner-if buys us anything here and the whole thing is
> equivalent to:
> if (mfn != INVALID_P2M_ENTRY)
> mfn &= ~(FOREIGN_FRAME_BIT|IDENTITY_FRAME_BIT);
>
> Not sure if the FOREIGN_FRAME_BIT|IDENTITY_FRAME_BIT construct gets
> enough use to be worthy of a #define FRAME_TYPE_MASK etc.

Yeah, that is much better.
>
> > return mfn;
> > }
> >
> > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> > index d98bd43..d470435 100644
> > --- a/arch/x86/xen/mmu.c
> > +++ b/arch/x86/xen/mmu.c
> > @@ -425,10 +425,10 @@ unsigned long get_phys_to_machine(unsigned long pfn)
> > * would be wrong.
> > */
> > if (p2m_top[topidx] == p2m_mid_identity)
> > - return pfn;
> > + return pfn | IDENTITY_FRAME_BIT;
>
> It's probably worth defining IDENTITY_FRAME(m) in the pattern of
> FOREIGN_FRAME(m).

<nods>