Re: [PATCH 3/4] VT-d: replace flush_all_cache()

[Andrew Cooper <amc96@xxxxxxxx>]

On 01/12/2021 09:41, Jan Beulich wrote:
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -591,7 +591,8 @@ static int __must_check iommu_flush_all(
>      bool_t flush_dev_iotlb;
>      int rc = 0;
>  
> -    flush_all_cache();
> +    flush_local(FLUSH_CACHE);

While I agree that the conversion is an improvement, the logic still
looks totally bogus.

I can believe that it might have been a stopgap to fix problems before
we identified the need for sync_cache() for non-coherent IOMMUs, but
there's no need I can spot for any WBINVDs on any of these paths.

I'm fairly sure this should just be dropped, and Xen will get faster as
a result.

~Andrew