Re: [Xen-devel] [PATCH RFC 1/3] x86: Make page cache mode a real type

[Juergen Gross <jgross@xxxxxxxx>]

On 08/22/2014 12:09 AM, Toshi Kani wrote:
> On Tue, 2014-08-19 at 15:25 +0200, jgross@xxxxxxxx wrote:
> > From: Juergen Gross <jgross@xxxxxxxx>
> >
> > At the moment there are a lot of places that handle setting or getting
> > the page cache mode by treating the pgprot bits equal to the cache mode.
> > This is only true because there are a lot of assumptions about the setup
> > of the PAT MSR. Otherwise the cache type needs to get translated into
> > pgprot bits and vice versa.
> >
> > This patch tries to prepare for that by introducing a seperate type
> > for the cache mode and adding functions to translate between those and pgprot
> > values.
> >
> > To avoid too much performance penalty the translation between cache mode
> > and pgprot values is done via tables which contain the relevant information.
> > Write-back cache mode is hard-wired to be 0, all other modes are configurable
> > via those tables. For large pages there are translation functions as the
> > PAT bit is located at different positions in the ptes of 4k and large pages.
> One more comment below..
>
> > diff --git a/arch/x86/include/asm/cacheflush.h 
> > b/arch/x86/include/asm/cacheflush.h
>   :
> > -static inline void set_page_memtype(struct page *pg, unsigned long memtype)
> > +static inline void set_page_memtype(struct page *pg,
> > +                                   enum page_cache_mode memtype)
> >   {
> >         unsigned long memtype_flags = _PGMT_DEFAULT;
> >         unsigned long old_flags;
> >         unsigned long new_flags;
> >
> >         switch (memtype) {
> > -       case _PAGE_CACHE_WC:
> > +       case _PAGE_CACHE_MODE_WC:
> >                 memtype_flags = _PGMT_WC;
> >                 break;
> > -       case _PAGE_CACHE_UC_MINUS:
> > +       case _PAGE_CACHE_MODE_UC_MINUS:
> >                 memtype_flags = _PGMT_UC_MINUS;
> >                 break;
> > -       case _PAGE_CACHE_WB:
> > +       case _PAGE_CACHE_MODE_WB:
> > +       default:
> >                 memtype_flags = _PGMT_WB;
> >                 break;
> >         }
> Adding the "default" case handled as _PGMT_WB is not correct here.
> free_ram_pages_type() calls set_page_memtype() with -1, which needs to
> be set to _PGMT_DEFAULT.
It says so in the comment above. I'll correct it, thanks.

Juergen


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