Re: [Xen-devel] [PATCH V2 1/3] x86: Make page cache mode a real type

[Juergen Gross <jgross@xxxxxxxx>]

On 09/09/2014 07:24 PM, Toshi Kani wrote:
> On Mon, 2014-09-08 at 10:01 +0200, Juergen Gross wrote:
> > 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.
> >
> > Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> I have two minor comments (which I should have caught before)... Other
> wise, the changes look good to me
>
> Reviewed-by: Toshi Kani <toshi.kani@xxxxxx>
>
>
> >   /*
> > diff --git a/arch/x86/include/asm/fb.h b/arch/x86/include/asm/fb.h
> > index 2519d06..0902a50 100644
> > --- a/arch/x86/include/asm/fb.h
> > +++ b/arch/x86/include/asm/fb.h
> > @@ -8,8 +8,12 @@
> >   static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma,
> >                                 unsigned long off)
> >   {
> > +       unsigned long prot;
> > +
> > +       prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
> >         if (boot_cpu_data.x86 > 3)
> > -               pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
> > +               pgprot_val(vma->vm_page_prot) =
> > +                       prot | cachemode2protval(_PAGE_CACHE_MODE_UC);
> This should be _PAGE_CACHE_MODE_UC_MINUS as the original code only sets
> the PCD bit.
Okay.

> > diff --git a/drivers/video/fbdev/gbefb.c b/drivers/video/fbdev/gbefb.c
> > index 4aa56ba..b1cc7a6 100644
> > --- a/drivers/video/fbdev/gbefb.c
> > +++ b/drivers/video/fbdev/gbefb.c
> > @@ -54,7 +54,8 @@ struct gbefb_par {
> >   #endif
> >   #endif
> >   #ifdef CONFIG_X86
> > -#define pgprot_fb(_prot) ((_prot) | _PAGE_PCD)
> > +#define pgprot_fb(_prot) (((_prot) & ~_PAGE_CACHE_MASK) |  \
> > +                         cachemode2protval(_PAGE_CACHE_MODE_UC))
> Ditto.
Yep.


Thanks,

Juergen

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