[Xen-devel] Re: [PATCH 04/10] xen/mmu: For 1-1 mapping, automatically set _PAGE_IOMAP.

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> This means that for PFNs (specifically: those in any E820 gaps
> or non-RAM E820 regions) that have 1-1 mapping we set the
> _PAGE_IOMAP flag.
>
> Later on we could remove the _PAGE_IOMAP code handling, but
> for right now lets keep this in to not introduce any bisection
> failures across this patchset.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  arch/x86/xen/mmu.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 4ba7e4e..bd02e7d 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -832,6 +832,9 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
>               pteval_t flags = val & PTE_FLAGS_MASK;
>               unsigned long mfn = pfn_to_mfn(pfn);
>  
> +             if (mfn == pfn)
> +                     flags |= _PAGE_IOMAP;

Why?  Does it really make sense to set _PAGE_IOMAP if they just happen
to be the same value?

    J

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