Merge branch 'master' of /home/davem/src/GIT/linux-2.6/

1 files changed, 23 insertions, 2 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 1d4eb93..cf07c26 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));