[RFC PATCH RESEND] x86/cpu: Avoid endless loop to get the number of cache leaves

[Pu Wen]

To get the number of cache leaves on AMD or Hygon platform, it should
get the value of cpuid leaf 0x8000001d. But on certain broken platform
such as a not fullly implemented virtual platform(for example Xen),
the value of the cpuid leaf will nerver be CTYPE_NULL, so the kernel
will run into an endless loop.

To fix this problem, add a new enum type CTYPE_MAX to limit the maximum
cpuid accessing.

Signed-off-by: Pu Wen <pu...@hygon.cn>
---
 arch/x86/kernel/cpu/cacheinfo.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index dc1b934..7bd167f 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -121,7 +121,8 @@ enum _cache_type {
        CTYPE_NULL = 0,
        CTYPE_DATA = 1,
        CTYPE_INST = 2,
-       CTYPE_UNIFIED = 3
+       CTYPE_UNIFIED = 3,
+       CTYPE_MAX = 4
 };
 
 union _cpuid4_leaf_eax {
@@ -640,7 +641,7 @@ static int find_num_cache_leaves(struct cpuinfo_x86 *c)
                /* Do cpuid(op) loop to find out num_cache_leaves */
                cpuid_count(op, i, &eax, &ebx, &ecx, &edx);
                cache_eax.full = eax;
-       } while (cache_eax.split.type != CTYPE_NULL);
+       } while (cache_eax.split.type != CTYPE_NULL && i != CTYPE_MAX);
        return i;
 }
 
-- 
2.7.4