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

[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 <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

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

[Borislav Petkov]

On Thu, Dec 06, 2018 at 03:26:13PM +0800, Pu Wen wrote:
> 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 <puwen@hygon.cn>
> ---
>  arch/x86/kernel/cpu/cacheinfo.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Did you not see my reply to this last time?

https://lkml.kernel.org/r/20181115172155.GB25056@zn.tnic

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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

[Pu Wen]

On 2018/12/6 18:37, Borislav Petkov wrote:
> Did you not see my reply to this last time?
>
> https://lkml.kernel.org/r/20181115172155.GB25056@zn.tnic

I'm sorry that there is something wrong with my mail filter. So I was
not notified about your reply for many days. :)

I just found your reply and replied to it.

Thx.

-- 
Regards,
Pu Wen

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

[Pu Wen]

On 2018/12/6 18:37, Borislav Petkov wrote:
 > Did you not see my reply to this last time?
 >
 > https://lkml.kernel.org/r/20181115172155.GB25056@zn.tnic

I'm sorry that there is something wrong with my mail filter. So I was
not notified about your reply for many days. :)

I just found your reply and replied to it.

Thx.

-- 
Regards,
Pu Wen