Re: [Xen-devel] [PATCH] xen/arm: define PAGE_HYPERVISOR as BUFFERABLE

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-06-04 at 14:29 +0100, Stefano Stabellini wrote:
> On Fri, 10 May 2013, Stefano Stabellini wrote:
> > Use stage 1 attribute indexes for PAGE_HYPERVISOR, the appriopriate one
> > for normal memory hypervisor mappings would be BUFFERABLE.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> >
> > diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
> > index fd6946e..13f76fc 100644
> > --- a/xen/include/asm-arm/page.h
> > +++ b/xen/include/asm-arm/page.h
> > @@ -58,7 +58,7 @@
> >  #define DEV_WC        BUFFERABLE
> >  #define DEV_CACHED    WRITEBACK
> >  
> > -#define PAGE_HYPERVISOR         (MATTR_MEM)
> > +#define PAGE_HYPERVISOR         (BUFFERABLE)
> >  #define MAP_SMALL_PAGES         PAGE_HYPERVISOR
> >  
> >  /*
>  
> This patch is completely wrong, fortunately it hasn't been applied.

Yes, it appears to have slipped through my net, sorry. (But good in this
case!)

> 
> Despite the name, BUFFERABLE means non-cacheable. Mapping a guest page
> non-cacheable in the hypervisor would cause mismatch in memory
> attributes.
> 
> We should map the guest page as "normal memory", that is WRITEBACK.

The hypervisor's own memory mappings are using WRITEALLOC not WRITEBACK
(see mfn_to_xen_entry). Is one or the other wrong?

> diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
> index fd6946e..13f76fc 100644
> --- a/xen/include/asm-arm/page.h
> +++ b/xen/include/asm-arm/page.h
> @@ -58,7 +58,7 @@
>  #define DEV_WC        BUFFERABLE
>  #define DEV_CACHED    WRITEBACK
>  
> -#define PAGE_HYPERVISOR         (MATTR_MEM)
> +#define PAGE_HYPERVISOR         (WRITEBACK)
>  #define MAP_SMALL_PAGES         PAGE_HYPERVISOR
>  
>  /*



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