Revert most of "x86: Fix alternatives and kprobes to remap write-protected kernel text"

This reverts most of commit 19d36ccdc34f5ed444f8a6af0cbfdb6790eb1177.

The way to DEBUG_RODATA interactions with KPROBES and CPU hotplug is to
just not mark the text as being write-protected in the first place.
Both of those facilities depend on rewriting instructions.

Having "helpful" debug facilities that just cause more problem is not
being helpful.  It just adds complexity and bugs. Not worth it.

Reported-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Andi Kleen <ak@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 23 insertions, 15 deletions

diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
index c3750c2..c85598a 100644
--- a/arch/i386/kernel/alternative.c
+++ b/arch/i386/kernel/alternative.c
@@ -430,22 +430,12 @@ void __init alternative_instructions(void)
  * And on the local CPU you need to be protected again NMI or MCE handlers
  * seeing an inconsistent instruction while you patch.
  */
-void __kprobes text_poke(void *oaddr, unsigned char *opcode, int len)
+void __kprobes text_poke(void *addr, unsigned char *opcode, int len)
 {
-        u8 *addr = oaddr;
-	if (!pte_write(*lookup_address((unsigned long)addr))) {
-		struct page *p[2] = { virt_to_page(addr), virt_to_page(addr+PAGE_SIZE) };
-		addr = vmap(p, 2, VM_MAP, PAGE_KERNEL);
-		if (!addr)
-			return;
-		addr += ((unsigned long)oaddr) % PAGE_SIZE;
-	}
 	memcpy(addr, opcode, len);
 	sync_core();
 	/* Not strictly needed, but can speed CPU recovery up. Ignore cross cacheline
 	   case. */
 	if (cpu_has_clflush)
-		asm("clflush (%0) " :: "r" (oaddr) : "memory");
-	if (addr != oaddr)
-		vunmap(addr);
+		asm("clflush (%0) " :: "r" (addr) : "memory");
 }
diff --git a/arch/i386/mm/init.c b/arch/i386/mm/init.c
index 1b1a1e6..4c4809f 100644
--- a/arch/i386/mm/init.c
+++ b/arch/i386/mm/init.c
@@ -800,9 +800,17 @@ void mark_rodata_ro(void)
 	unsigned long start = PFN_ALIGN(_text);
 	unsigned long size = PFN_ALIGN(_etext) - start;
 
-	change_page_attr(virt_to_page(start),
-	                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
-	printk("Write protecting the kernel text: %luk\n", size >> 10);
+#ifndef CONFIG_KPROBES
+#ifdef CONFIG_HOTPLUG_CPU
+	/* It must still be possible to apply SMP alternatives. */
+	if (num_possible_cpus() <= 1)
+#endif
+	{
+		change_page_attr(virt_to_page(start),
+		                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
+		printk("Write protecting the kernel text: %luk\n", size >> 10);
+	}
+#endif
 	start += size;
 	size = (unsigned long)__end_rodata - start;
 	change_page_attr(virt_to_page(start),
diff --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
index 38f5d63..458893b 100644
--- a/arch/x86_64/mm/init.c
+++ b/arch/x86_64/mm/init.c
@@ -600,6 +600,16 @@ void mark_rodata_ro(void)
 {
 	unsigned long start = (unsigned long)_stext, end;
 
+#ifdef CONFIG_HOTPLUG_CPU
+	/* It must still be possible to apply SMP alternatives. */
+	if (num_possible_cpus() > 1)
+		start = (unsigned long)_etext;
+#endif
+
+#ifdef CONFIG_KPROBES
+	start = (unsigned long)__start_rodata;
+#endif
+	
 	end = (unsigned long)__end_rodata;
 	start = (start + PAGE_SIZE - 1) & PAGE_MASK;
 	end &= PAGE_MASK;