i386: Make patching more robust, fix paravirt issue

Commit 19d36ccdc34f5ed444f8a6af0cbfdb6790eb1177 "x86: Fix alternatives
and kprobes to remap write-protected kernel text" uses code which is
being patched for patching.

In particular, paravirt_ops does patching in two stages: first it
calls paravirt_ops.patch, then it fills any remaining instructions
with nop_out().  nop_out calls text_poke() which calls
lookup_address() which calls pgd_val() (aka paravirt_ops.pgd_val):
that call site is one of the places we patch.

If we always do patching as one single call to text_poke(), we only
need make sure we're not patching the memcpy in text_poke itself.
This means the prototype to paravirt_ops.patch needs to change, to
marshal the new code into a buffer rather than patching in place as it
does now.  It also means all patching goes through text_poke(), which
is known to be safe (apply_alternatives is also changed to make a
single patch).

AK: fix compilation on x86-64 (bad rusty!)
AK: fix boot on x86-64 (sigh)
AK: merged with other patches

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/lguest/lguest.c b/drivers/lguest/lguest.c
index 524beea..6e135ac 100644
--- a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -936,23 +936,24 @@ static const struct lguest_insns
 /* Now our patch routine is fairly simple (based on the native one in
  * paravirt.c).  If we have a replacement, we copy it in and return how much of
  * the available space we used. */
-static unsigned lguest_patch(u8 type, u16 clobber, void *insns, unsigned len)
+static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
+			     unsigned long addr, unsigned len)
 {
 	unsigned int insn_len;
 
 	/* Don't do anything special if we don't have a replacement */
 	if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
-		return paravirt_patch_default(type, clobber, insns, len);
+		return paravirt_patch_default(type, clobber, ibuf, addr, len);
 
 	insn_len = lguest_insns[type].end - lguest_insns[type].start;
 
 	/* Similarly if we can't fit replacement (shouldn't happen, but let's
 	 * be thorough). */
 	if (len < insn_len)
-		return paravirt_patch_default(type, clobber, insns, len);
+		return paravirt_patch_default(type, clobber, ibuf, addr, len);
 
 	/* Copy in our instructions. */
-	memcpy(insns, lguest_insns[type].start, insn_len);
+	memcpy(ibuf, lguest_insns[type].start, insn_len);
 	return insn_len;
 }