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

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.


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 {
  #ifdef CONFIG_X86
-#define pgprot_fb(_prot) ((_prot) | _PAGE_PCD)
+#define pgprot_fb(_prot) (((_prot) & ~_PAGE_CACHE_MASK) |  \
+                         cachemode2protval(_PAGE_CACHE_MODE_UC))





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