Re: [Xen-devel] [PATCH] x86: don't use VA for cache flush when also flushing TLB

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.05.14 at 06:35, <yang.z.zhang@xxxxxxxxx> wrote:
> Besides, I am thinking should we flush cache unconditionally, e.g., if all 
> agents that able to access memory have the snooping capability, then software 
> is not required to flush cache always.(If I am wrong, please correct me and 
> ignore the following changes). So is there any problem with this change?
> @@ -145,7 +145,7 @@ void flush_area_local(const void *va, unsigned int flags)
>          }
>      }
>  
> -    if ( flags & FLUSH_CACHE )
> +    if ( flags & FLUSH_CACHE && !(iommu_enable && iommu_snoop))
>      {
>          unsigned long i, sz = 0;

At least the iommu_snoop part was discussed at length a couple
of weeks back: I don't see how this relates to cache flushing
requirements. I also don't see how IOMMU presence/absence
would matter here - the behavior should clearly be identical
between systems with and without IOMMU.

Jan


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