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

[Juergen Gross]

On 08/26/2014 09:44 PM, Toshi Kani wrote:
> On Tue, 2014-08-26 at 08:16 +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>
>
> Hi Juergen,
>
> Thanks for the updates!  A few comments below...
>
> > @@ -73,6 +73,9 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
> >   /*
> >    * Map 'pfn' using protections 'prot'
> >    */
> > +#define __PAGE_KERNEL_WC	(__PAGE_KERNEL | \
> > +				 cachemode2protval(_PAGE_CACHE_MODE_WC))
> > +
> >   void __iomem *
> >   iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
> >   {
> > @@ -82,12 +85,14 @@ iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
> >   	 * MTRR is UC or WC.  UC_MINUS gets the real intention, of the
> >   	 * user, which is "WC if the MTRR is WC, UC if you can't do that."
> >   	 */
> > -	if (!pat_enabled && pgprot_val(prot) == pgprot_val(PAGE_KERNEL_WC))
> > -		prot = PAGE_KERNEL_UC_MINUS;
> > +	if (!pat_enabled && pgprot_val(prot) == __PAGE_KERNEL_WC)
> > +		prot = __pgprot(__PAGE_KERNEL |
> > +				protval_pagemode(_PAGE_CACHE_MODE_UC_MINUS));
>
> protval_pagemode() should be cachemode2protval().

Obviously, yes.

> >   /*
> > diff --git a/drivers/video/fbdev/vermilion/vermilion.c b/drivers/video/fbdev/vermilion/vermilion.c
> > index 048a666..6bbc559 100644
> > --- a/drivers/video/fbdev/vermilion/vermilion.c
> > +++ b/drivers/video/fbdev/vermilion/vermilion.c
> > @@ -1004,13 +1004,15 @@ static int vmlfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
> >   	struct vml_info *vinfo = container_of(info, struct vml_info, info);
> >   	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
> >   	int ret;
> > +	unsigned long prot;
> >
> >   	ret = vmlfb_vram_offset(vinfo, offset);
> >   	if (ret)
> >   		return -EINVAL;
> >
> > -	pgprot_val(vma->vm_page_prot) |= _PAGE_PCD;
> > -	pgprot_val(vma->vm_page_prot) &= ~_PAGE_PWT;
> > +	prot = pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK;
> > +	pgprot_val(vma->vm_page_prot) =
> > +		prot | cachemode2protval(_PAGE_CACHE_MODE_UC);
>
> This cache mode should be _PAGE_CACHE_MODE_UC_MINUS as the original code
> only sets the PCD bit.

I'll change it.

Thanks,

Juergen

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