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

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

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.

>       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).

Ian.


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