[mm patch] i915: fix invalid opcode exception on cpus without clflush

[mm patch] i915: fix invalid opcode exception on cpus without clflush

[Kyle McMartin]

i915_flush_ttm was unconditionally executing a clflush instruction
to (obviously) flush the cache. Instead, check if the cpu supports
clflush, and if not, fall back to calling wbinvd to flush the entire
cache.

Signed-off-by: Kyle McMartin <kmcmartin@redhat.com>

--- a/drivers/char/drm/i915_buffer.c
+++ b/drivers/char/drm/i915_buffer.c
@@ -286,7 +286,18 @@ void i915_flush_ttm(struct drm_ttm *ttm)
 		return;
 
 	DRM_MEMORYBARRIER();
+
+#ifdef CONFIG_X86_32
+	/* Hopefully nobody has built an x86-64 processor without clflush */
+	if (!cpu_has_clflush) {
+		wbinvd();
+		DRM_MEMORYBARRIER();
+		return;
+	}
+#endif
+
 	for (i = ttm->num_pages - 1; i >= 0; i--)
 		drm_cache_flush_page(drm_ttm_get_page(ttm, i));
+
 	DRM_MEMORYBARRIER();
 }

Re: [mm patch] i915: fix invalid opcode exception on cpus without clflush

[H. Peter Anvin]

Kyle McMartin wrote:
> i915_flush_ttm was unconditionally executing a clflush instruction
> to (obviously) flush the cache. Instead, check if the cpu supports
> clflush, and if not, fall back to calling wbinvd to flush the entire
> cache.
> 
> Signed-off-by: Kyle McMartin <kmcmartin@redhat.com>
> 
> --- a/drivers/char/drm/i915_buffer.c
> +++ b/drivers/char/drm/i915_buffer.c
> @@ -286,7 +286,18 @@ void i915_flush_ttm(struct drm_ttm *ttm)
>  		return;
>  
>  	DRM_MEMORYBARRIER();
> +
> +#ifdef CONFIG_X86_32
> +	/* Hopefully nobody has built an x86-64 processor without clflush */
> +	if (!cpu_has_clflush) {
> +		wbinvd();
> +		DRM_MEMORYBARRIER();
> +		return;
> +	}
> +#endif
> +
>  	for (i = ttm->num_pages - 1; i >= 0; i--)
>  		drm_cache_flush_page(drm_ttm_get_page(ttm, i));
> +
>  	DRM_MEMORYBARRIER();
>  }

The #ifdef is bogus.  If it's required, it should go into 
asm-x86/required_features.h and then cpu_has_clflush is static; 
otherwise it's just plain wrong.

	-hpa

Re: [mm patch] i915: fix invalid opcode exception on cpus without clflush

[Harvey Harrison]

On Thu, 2008-01-17 at 21:03 -0500, H. Peter Anvin wrote:
> Kyle McMartin wrote:
> > i915_flush_ttm was unconditionally executing a clflush instruction
> > to (obviously) flush the cache. Instead, check if the cpu supports
> > clflush, and if not, fall back to calling wbinvd to flush the entire
> > cache.
> > 
> > Signed-off-by: Kyle McMartin <kmcmartin@redhat.com>
> > 
> > --- a/drivers/char/drm/i915_buffer.c
> > +++ b/drivers/char/drm/i915_buffer.c
> > @@ -286,7 +286,18 @@ void i915_flush_ttm(struct drm_ttm *ttm)
> >  		return;
> >  
> >  	DRM_MEMORYBARRIER();
> > +
> > +#ifdef CONFIG_X86_32
> > +	/* Hopefully nobody has built an x86-64 processor without clflush */
> > +	if (!cpu_has_clflush) {
> > +		wbinvd();
> > +		DRM_MEMORYBARRIER();
> > +		return;
> > +	}
> > +#endif
> > +
> >  	for (i = ttm->num_pages - 1; i >= 0; i--)
> >  		drm_cache_flush_page(drm_ttm_get_page(ttm, i));
> > +
> >  	DRM_MEMORYBARRIER();
> >  }
> 
> The #ifdef is bogus.  If it's required, it should go into 
> asm-x86/required_features.h and then cpu_has_clflush is static; 
> otherwise it's just plain wrong.

I think Andi's CPA patches have some changes regarding wbinvd and
clflush handling, perhaps you can leverage some of his work?

Harvey

Re: [mm patch] i915: fix invalid opcode exception on cpus without clflush

[Kyle McMartin]

On Thu, Jan 17, 2008 at 09:03:17PM -0500, H. Peter Anvin wrote:
> The #ifdef is bogus.  If it's required, it should go into 
> asm-x86/required_features.h and then cpu_has_clflush is static; otherwise 
> it's just plain wrong.
>

I have no objection to making cpu_has_clflush constant on x86_64. The
point was to get rid of a needless test & branch on 64-bit, and making
it constant will have the same effect.

cheers, Kyle