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

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>

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 0be9f9c59aa6b72d1cf55a0819be146d78f56e61..6d02a36e5e49209cf8f606769966ccda4f12a1be 100644 (file)
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -176,11 +176,11 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
                /*
                 * Do not fallback to certain memory types with certain
                 * requested type:
-                * - request is uncached, return cannot be write-back
-                * - request is uncached, return cannot be write-combine
+                * - request is uc-, return cannot be write-back
+                * - request is uc-, return cannot be write-combine
                 * - request is write-combine, return cannot be write-back
                 */
-               if ((prot_val == _PAGE_CACHE_UC &&
+               if ((prot_val == _PAGE_CACHE_UC_MINUS &&
                     (new_prot_val == _PAGE_CACHE_WB ||
                      new_prot_val == _PAGE_CACHE_WC)) ||
                    (prot_val == _PAGE_CACHE_WC &&
@@ -201,6 +201,9 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
        default:
                prot = PAGE_KERNEL_NOCACHE;
                break;
+       case _PAGE_CACHE_UC_MINUS:
+               prot = PAGE_KERNEL_UC_MINUS;
+               break;
        case _PAGE_CACHE_WC:
                prot = PAGE_KERNEL_WC;
                break;
@@ -255,7 +258,16 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
  */
 void __iomem *ioremap_nocache(resource_size_t phys_addr, unsigned long size)
 {
-       return __ioremap_caller(phys_addr, size, _PAGE_CACHE_UC,
+       /*
+        * Ideally, this should be:
+        *      pat_wc_enabled ? _PAGE_CACHE_UC : _PAGE_CACHE_UC_MINUS;
+        *
+        * Till we fix all X drivers to use ioremap_wc(), we will use
+        * UC MINUS.
+        */
+       unsigned long val = _PAGE_CACHE_UC_MINUS;
+
+       return __ioremap_caller(phys_addr, size, val,
                                __builtin_return_address(0));
 }
 EXPORT_SYMBOL(ioremap_nocache);

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index bd5e05c654dccfb33d368718e4b7acdbdd16d5d0..60bcb5b6a37ef0130fb08da8ef38db58fd37910a 100644 (file)
--- 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);

diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 94f6c73a53d0aae6ac048668ea6b06a0a1f370d0..8af0f0bae2af45f0baca08051056946235db7d1e 100644 (file)
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -301,6 +301,13 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
        prot = pgprot_val(vma->vm_page_prot);
        if (pat_wc_enabled && write_combine)
                prot |= _PAGE_CACHE_WC;
+       else if (pat_wc_enabled)
+               /*
+                * ioremap() and ioremap_nocache() defaults to UC MINUS for now.
+                * To avoid attribute conflicts, request UC MINUS here
+                * aswell.
+                */
+               prot |= _PAGE_CACHE_UC_MINUS;
        else if (boot_cpu_data.x86 > 3)
                prot |= _PAGE_CACHE_UC;
 
@@ -319,9 +326,8 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
                 * - request is uncached, return cannot be write-combine
                 * - request is write-combine, return cannot be write-back
                 */
-               if ((flags == _PAGE_CACHE_UC &&
-                    (new_flags == _PAGE_CACHE_WB ||
-                     new_flags == _PAGE_CACHE_WC)) ||
+               if ((flags == _PAGE_CACHE_UC_MINUS &&
+                    (new_flags == _PAGE_CACHE_WB)) ||
                    (flags == _PAGE_CACHE_WC &&
                     new_flags == _PAGE_CACHE_WB)) {
                        free_memtype(addr, addr+len);