[POWERPC] 4xx: Deal with 44x virtually tagged icache

The 44x family has an interesting "feature" which is a virtually
tagged instruction cache (yuck !). So far, we haven't dealt with
it properly, which means we've been mostly lucky or people didn't
report the problems, unless people have been running custom patches
in their distro...

This is an attempt at fixing it properly. I chose to do it by
setting a global flag whenever we change a PTE that was previously
marked executable, and flush the entire instruction cache upon
return to user space when that happens.

This is a bit heavy handed, but it's hard to do more fine grained
flushes as the icbi instruction, on those processor, for some very
strange reasons (since the cache is virtually mapped) still requires
a valid TLB entry for reading in the target address space, which
isn't something I want to deal with.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 21d889e63e87..a7572cf464bd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -244,6 +244,13 @@ syscall_exit_cont:
         andis.  r10,r0,DBCR0_IC@h
         bnel-   load_dbcr0
 #endif
+#ifdef CONFIG_44x
+        lis     r4,icache_44x_need_flush@ha
+        lwz     r5,icache_44x_need_flush@l(r4)
+        cmplwi  cr0,r5,0
+        bne-    2f
+1:
+#endif /* CONFIG_44x */
         stwcx.  r0,0,r1                 /* to clear the reservation */
         lwz     r4,_LINK(r1)
         lwz     r5,_CCR(r1)
@@ -258,6 +265,12 @@ syscall_exit_cont:
         mtspr   SPRN_SRR1,r8
         SYNC
         RFI
+#ifdef CONFIG_44x
+2:      li      r7,0
+        iccci   r0,r0
+        stw     r7,icache_44x_need_flush@l(r4)
+        b       1b
+#endif  /* CONFIG_44x */
 
 66:     li      r3,-ENOSYS
         b       ret_from_syscall
@@ -683,6 +696,16 @@ resume_kernel:
 
         /* interrupts are hard-disabled at this point */
 restore:
+#ifdef CONFIG_44x
+        lis     r4,icache_44x_need_flush@ha
+        lwz     r5,icache_44x_need_flush@l(r4)
+        cmplwi  cr0,r5,0
+        beq+    1f
+        li      r6,0
+        iccci   r0,r0
+        stw     r6,icache_44x_need_flush@l(r4)
+1:
+#endif  /* CONFIG_44x */
         lwz     r0,GPR0(r1)
         lwz     r2,GPR2(r1)
         REST_4GPRS(3, r1)