Revert "x86 PAT: remove CPA WARN_ON for zero pte"

This reverts commit 58dab916dfb57328d50deb0aa9b3fc92efa248ff, which
makes my Nehalem come to a nasty crawling almost-halt.  It looks like it
turns off caching of regular kernel RAM, with the understandable
slowdown of a few orders of magnitude as a result.

Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 32 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 160c42d3eb8f..8b08fb955274 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -505,35 +505,6 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 }
 #endif /* CONFIG_STRICT_DEVMEM */
 
-/*
- * Change the memory type for the physial address range in kernel identity
- * mapping space if that range is a part of identity map.
- */
-static int kernel_map_sync_memtype(u64 base, unsigned long size,
-                                        unsigned long flags)
-{
-        unsigned long id_sz;
-        int ret;
-
-        if (!pat_enabled || base >= __pa(high_memory))
-                return 0;
-
-        id_sz = (__pa(high_memory) < base + size) ?
-                                                __pa(high_memory) - base :
-                                                size;
-
-        ret = ioremap_change_attr((unsigned long)__va(base), id_sz, flags);
-        /*
-         * -EFAULT return means that the addr was not valid and did not have
-         * any identity mapping. That case is a success for
-         * kernel_map_sync_memtype.
-         */
-        if (ret == -EFAULT)
-                ret = 0;
-
-        return ret;
-}
-
 int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
                                 unsigned long size, pgprot_t *vma_prot)
 {
@@ -584,7 +555,9 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
         if (retval < 0)
                 return 0;
 
-        if (kernel_map_sync_memtype(offset, size, flags)) {
+        if (((pfn < max_low_pfn_mapped) ||
+             (pfn >= (1UL<<(32 - PAGE_SHIFT)) && pfn < max_pfn_mapped)) &&
+            ioremap_change_attr((unsigned long)__va(offset), size, flags) < 0) {
                 free_memtype(offset, offset + size);
                 printk(KERN_INFO
                 "%s:%d /dev/mem ioremap_change_attr failed %s for %Lx-%Lx\n",
@@ -632,7 +605,7 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
                                 int strict_prot)
 {
         int is_ram = 0;
-        int ret;
+        int id_sz, ret;
         unsigned long flags;
         unsigned long want_flags = (pgprot_val(*vma_prot) & _PAGE_CACHE_MASK);
 
@@ -673,7 +646,15 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
                                      flags);
         }
 
-        if (kernel_map_sync_memtype(paddr, size, flags)) {
+        /* Need to keep identity mapping in sync */
+        if (paddr >= __pa(high_memory))
+                return 0;
+
+        id_sz = (__pa(high_memory) < paddr + size) ?
+                                __pa(high_memory) - paddr :
+                                size;
+
+        if (ioremap_change_attr((unsigned long)__va(paddr), id_sz, flags) < 0) {
                 free_memtype(paddr, paddr + size);
                 printk(KERN_ERR
                         "%s:%d reserve_pfn_range ioremap_change_attr failed %s "