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x86: use default cache size if it cannot be determined [BZ #28784]

Message ID 20220115101327.661190-1-aurelien@aurel32.net
State Committed
Commit c242fcce06e3102ca663b2f992611d0bda4f2668
Headers show
Series x86: use default cache size if it cannot be determined [BZ #28784] | expand

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

Aurelien Jarno Jan. 15, 2022, 10:13 a.m. UTC
In some cases (e.g QEMU, non-Intel/AMD CPU) the cache information can
not be retrieved and the corresponding values are set to 0.

Commit 2d651eb9265d ("x86: Move x86 processor cache info to
cpu_features") changed the behaviour in such case by defining the
__x86_shared_cache_size and __x86_data_cache_size variables to 0 instead
of using the default values. This cause an issue with the i686 SSE2
optimized bzero/routine which assumes that the cache size is at least
128 bytes, and otherwise tries to zero/set the whole address space minus
128 bytes.

Fix that by restoring the original code to only update
__x86_shared_cache_size and __x86_data_cache_size variables if the
corresponding cache sizes are not zero.

Fixes bug 28784
Fixes commit 2d651eb9265d
---
 sysdeps/x86/cacheinfo.h | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

Comments

H.J. Lu Jan. 15, 2022, 12:28 p.m. UTC | #1
On Sat, Jan 15, 2022 at 2:13 AM Aurelien Jarno <aurelien@aurel32.net> wrote:
>
> In some cases (e.g QEMU, non-Intel/AMD CPU) the cache information can
> not be retrieved and the corresponding values are set to 0.
>
> Commit 2d651eb9265d ("x86: Move x86 processor cache info to
> cpu_features") changed the behaviour in such case by defining the
> __x86_shared_cache_size and __x86_data_cache_size variables to 0 instead
> of using the default values. This cause an issue with the i686 SSE2
> optimized bzero/routine which assumes that the cache size is at least
> 128 bytes, and otherwise tries to zero/set the whole address space minus
> 128 bytes.
>
> Fix that by restoring the original code to only update
> __x86_shared_cache_size and __x86_data_cache_size variables if the
> corresponding cache sizes are not zero.
>
> Fixes bug 28784
> Fixes commit 2d651eb9265d
> ---
>  sysdeps/x86/cacheinfo.h | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/sysdeps/x86/cacheinfo.h b/sysdeps/x86/cacheinfo.h
> index 4f91a1e98d..65132a9d19 100644
> --- a/sysdeps/x86/cacheinfo.h
> +++ b/sysdeps/x86/cacheinfo.h
> @@ -61,14 +61,20 @@ init_cacheinfo (void)
>    long int data = cpu_features->data_cache_size;
>    /* Round data cache size to multiple of 256 bytes.  */
>    data = data & ~255L;
> -  __x86_data_cache_size_half = data / 2;
> -  __x86_data_cache_size = data;
> +  if (data > 0)
> +    {
> +      __x86_data_cache_size_half = data / 2;
> +      __x86_data_cache_size = data;
> +    }
>
>    long int shared = cpu_features->shared_cache_size;
>    /* Round shared cache size to multiple of 256 bytes.  */
>    shared = shared & ~255L;
> -  __x86_shared_cache_size_half = shared / 2;
> -  __x86_shared_cache_size = shared;
> +  if (shared > 0)
> +    {
> +      __x86_shared_cache_size_half = shared / 2;
> +      __x86_shared_cache_size = shared;
> +    }
>
>    __x86_shared_non_temporal_threshold
>      = cpu_features->non_temporal_threshold;
> --
> 2.34.1
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.
diff mbox series

Patch

diff --git a/sysdeps/x86/cacheinfo.h b/sysdeps/x86/cacheinfo.h
index 4f91a1e98d..65132a9d19 100644
--- a/sysdeps/x86/cacheinfo.h
+++ b/sysdeps/x86/cacheinfo.h
@@ -61,14 +61,20 @@  init_cacheinfo (void)
   long int data = cpu_features->data_cache_size;
   /* Round data cache size to multiple of 256 bytes.  */
   data = data & ~255L;
-  __x86_data_cache_size_half = data / 2;
-  __x86_data_cache_size = data;
+  if (data > 0)
+    {
+      __x86_data_cache_size_half = data / 2;
+      __x86_data_cache_size = data;
+    }
 
   long int shared = cpu_features->shared_cache_size;
   /* Round shared cache size to multiple of 256 bytes.  */
   shared = shared & ~255L;
-  __x86_shared_cache_size_half = shared / 2;
-  __x86_shared_cache_size = shared;
+  if (shared > 0)
+    {
+      __x86_shared_cache_size_half = shared / 2;
+      __x86_shared_cache_size = shared;
+    }
 
   __x86_shared_non_temporal_threshold
     = cpu_features->non_temporal_threshold;