arm: Fix 32-bit ARM handling of the CTR register

When booting on an ARMv8 core that implements either CTR.IDC or CTR.DIC
(indicating that some of the cache maintenance operations can be
removed when dealing with I/D-cache coherency, GRUB dies with a
"Unsupported cache type 0x........" message.

This is pretty likely to happen when running in a virtual machine
hosted on an arm64 machine (I've triggered it on a system built around
a bunch of Cortex-A55 cores, which implements CTR.IDC).

It turns out that the way GRUB deals with the CTR register is a bit
harsh for anything from ARMv7 onwards. The layout of the register is
backward compatible, meaning that nothing that gets added is allowed to
break earlier behaviour. In this case, ignoring IDC is completely fine,
and only results in unnecessary cache maintenance.

We can thus avoid being paranoid, and align the 32bit behaviour with
its 64bit equivalent.

This patch has the added benefit that it gets rid of a (gnu-specific)
case range too.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/kern/arm/cache.c b/grub-core/kern/arm/cache.c
index af1c4bbf544f0ebcca5c0f58c847c8dddc1f2e91..6c75193e4ac480a23c6a68bc52f06ec641c8d919 100644 (file)
--- a/grub-core/kern/arm/cache.c
+++ b/grub-core/kern/arm/cache.c
@@ -93,13 +93,16 @@ probe_caches (void)
       grub_arch_cache_ilinesz = 8 << (cache_type & 3);
       type = ARCH_ARMV6;
       break;
-    case 0x80 ... 0x8f:
+    default:
+      /*
+       * The CTR register is pretty much unchanged from v7 onwards,
+       * and is guaranteed to be backward compatible (the IDC/DIC bits
+       * allow certain CMOs to be elided, but performing them is never
+       * wrong), hence handling it like its AArch64 equivalent.
+       */
       grub_arch_cache_dlinesz = 4 << ((cache_type >> 16) & 0xf);
       grub_arch_cache_ilinesz = 4 << (cache_type & 0xf);
       type = ARCH_ARMV7;
-      break;
-    default:
-      grub_fatal ("Unsupported cache type 0x%x", cache_type);
     }
   if (grub_arch_cache_dlinesz > grub_arch_cache_ilinesz)
     grub_arch_cache_max_linesz = grub_arch_cache_dlinesz;