powerpc/64s: Default l1d_size to 64K in RFI fallback flush

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit 9dfbf78e4114fcaf4ef61c49885c3ab5bad40d0b ]

If there is no d-cache-size property in the device tree, l1d_size could
be zero. We don't actually expect that to happen, it's only been seen
on mambo (simulator) in some configurations.

A zero-size l1d_size leads to the loop in the asm wrapping around to
2^64-1, and then walking off the end of the fallback area and
eventually causing a page fault which is fatal.

Just default to 64K which is correct on some CPUs, and sane enough to
not cause a crash on others.

Fixes: aa8a5e0062ac9 ('powerpc/64s: Add support for RFI flush of L1-D cache')
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
[mpe: Rewrite comment and change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 4abb684584dcc4d1f69d2273ddaac401198355c0..78a71b4fd646f59d116ba1e80f150ebdc7fdb359 100644 (file)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -858,6 +858,17 @@ static void __ref init_fallback_flush(void)
                return;
 
        l1d_size = ppc64_caches.l1d.size;
+
+       /*
+        * If there is no d-cache-size property in the device tree, l1d_size
+        * could be zero. That leads to the loop in the asm wrapping around to
+        * 2^64-1, and then walking off the end of the fallback area and
+        * eventually causing a page fault which is fatal. Just default to
+        * something vaguely sane.
+        */
+       if (!l1d_size)
+               l1d_size = (64 * 1024);
+
        limit = min(safe_stack_limit(), ppc64_rma_size);
 
        /*