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From:   Pu Wen <puwen@hygon.cn>
To:     <bp@alien8.de>, <tglx@linutronix.de>, <mingo@redhat.com>,
        <hpa@zytor.com>, <x86@kernel.org>, <linux-kernel@vger.kernel.org>
CC:     Pu Wen <puwen@hygon.cn>
Subject: [PATCH] x86/cpu: Avoid endless loop to get the number of cache leaves
Date:   Mon, 5 Nov 2018 20:53:45 +0800
Message-ID: <1541422425-5855-1-git-send-email-puwen@hygon.cn>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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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(Xen, for example),
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 <puwen@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