Merge master.kernel.org:/pub/scm/linux/kernel/git/lethal/genesis-2.6

1 files changed, 23 insertions, 2 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 1d4eb93d333c..cf07c26d9a4a 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -291,8 +291,29 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
          */
         if (kernel_set_to_readonly &&
             within(address, (unsigned long)_text,
-                   (unsigned long)__end_rodata_hpage_align))
-                pgprot_val(forbidden) |= _PAGE_RW;
+                   (unsigned long)__end_rodata_hpage_align)) {
+                unsigned int level;
+
+                /*
+                 * Don't enforce the !RW mapping for the kernel text mapping,
+                 * if the current mapping is already using small page mapping.
+                 * No need to work hard to preserve large page mappings in this
+                 * case.
+                 *
+                 * This also fixes the Linux Xen paravirt guest boot failure
+                 * (because of unexpected read-only mappings for kernel identity
+                 * mappings). In this paravirt guest case, the kernel text
+                 * mapping and the kernel identity mapping share the same
+                 * page-table pages. Thus we can't really use different
+                 * protections for the kernel text and identity mappings. Also,
+                 * these shared mappings are made of small page mappings.
+                 * Thus this don't enforce !RW mapping for small page kernel
+                 * text mapping logic will help Linux Xen parvirt guest boot
+                 * aswell.
+                 */
+                if (lookup_address(address, &level) && (level != PG_LEVEL_4K))
+                        pgprot_val(forbidden) |= _PAGE_RW;
+        }
 #endif
 
         prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));