Re: [PATCH] powerpc/8xx: fix regression introduced by cache coherency rewrite

[Joakim Tjernlund <joakim.tjernlund@transmode.se>]

Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote on 29/09/2009 09:07:37:
>
> On Tue, 2009-09-29 at 08:26 +0200, Joakim Tjernlund wrote:
> > > I've tried sticking tlbil_va() in those places, nothing seems to
> > help.
> > > In some cases userspace is slow, in other cases userspace is faster
> > and
> > > unstable: sometimes commands hang, sometimes I am able to ctrl-c and
> > > and kill it, sometimes I get other strange crashes or falures (so
> > far no
> > > kernel oopses though).
> >
> > This is exactly what you get when the "cache insn does not update DAR"
> > bug hits
> > you.
>
> But then why was it working fine before ? Or it wasn't ?

hmm, yes. You do get this and mysterious SEGV if you hit the but so does
other bugs too so this is probably due to missing invalidation.

I suspect that something like below will fix the problem and
is the "correct" fix(untested, not even compiled):

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 52ff8c5..f579a11 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -428,7 +428,7 @@ DataStoreTLBMiss:
 	 * set.  All other Linux PTE bits control the behavior
 	 * of the MMU.
 	 */
-2:	li	r11, 0x00f0
+	li	r11, 0x00f0
 	rlwimi	r10, r11, 0, 24, 28	/* Set 24-27, clear 28 */
 	DO_8xx_CPU6(0x3d80, r3)
 	mtspr	SPRN_MD_RPN, r10	/* Update TLB entry */
@@ -441,7 +441,23 @@ DataStoreTLBMiss:
 	lwz	r3, 8(r0)
 #endif
 	rfi
+2:
+	/* Copy 20 msb from MD_EPN to DAR since the dcxx instructions fails
+	 * to update DAR when they cause a DTLB Miss.
+	 */
+	mfspr	r11, SPRN_MD_EPN
+	mfspr	r10, SPRN_DAR
+	rlwimi	r10, r11, 0, 0, 19
+	mtspr	SPRN_DAR, r10

+	mfspr	r10, SPRN_M_TW	/* Restore registers */
+	lwz	r11, 0(r0)
+	mtcr	r11
+	lwz	r11, 4(r0)
+#ifdef CONFIG_8xx_CPU6
+	lwz	r3, 8(r0)
+#endif
+	b	DataAccess
 /* This is an instruction TLB error on the MPC8xx.  This could be due
  * to many reasons, such as executing guarded memory or illegal instruction
  * addresses.  There is nothing to do but handle a big time error fault.