x86 PAT: fix performance drop for glx, use UC minus for ioremap(), ioremap_nocache() and pci_mmap_page_range()

Use UC_MINUS for ioremap(), ioremap_nocache() instead of strong UC.
Once all the X drivers move to ioremap_wc(), we can go back to strong
UC semantics for ioremap() and ioremap_nocache().

To avoid attribute aliasing issues, pci_mmap_page_range() will also
use UC_MINUS for default non write-combining mapping request.

Next steps:
	a) change all the video drivers using ioremap() or ioremap_nocache()
	   and adding WC MTTR using mttr_add() to ioremap_wc()

	b) for strict usage, we can go back to strong uc semantics
	   for ioremap() and ioremap_nocache() after some grace period for
	   completing step-a.

	c) user level X server needs to use the appropriate method for setting
	   up WC mapping (like using resourceX_wc sysfs file instead of
	   adding MTRR for WC and using /dev/mem or resourceX under /sys)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index bd5e05c654dc..60bcb5b6a37e 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -777,14 +777,20 @@ static inline int change_page_attr_clear(unsigned long addr, int numpages,
 
 int _set_memory_uc(unsigned long addr, int numpages)
 {
+        /*
+         * for now UC MINUS. see comments in ioremap_nocache()
+         */
         return change_page_attr_set(addr, numpages,
-                                    __pgprot(_PAGE_CACHE_UC));
+                                    __pgprot(_PAGE_CACHE_UC_MINUS));
 }
 
 int set_memory_uc(unsigned long addr, int numpages)
 {
+        /*
+         * for now UC MINUS. see comments in ioremap_nocache()
+         */
         if (reserve_memtype(addr, addr + numpages * PAGE_SIZE,
-                            _PAGE_CACHE_UC, NULL))
+                            _PAGE_CACHE_UC_MINUS, NULL))
                 return -EINVAL;
 
         return _set_memory_uc(addr, numpages);