Re: [Xen-devel] [PATCH v2 2.5/4] xen/x86: Replace mandatory barriers with compiler barriers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.08.17 at 19:18, <andrew.cooper3@xxxxxxxxxx> wrote:
> In this case, rmb() is being used for its compiler barrier property.  Replace
> it with an explicit barrer() and comment, to avoid it becoming an 
> unnecessary
> lfence instruction (when rmb() gets fixed) or looking like an SMP issue.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

But you forgot to Cc Suravee (now done), for him to have a chance
to ack the change.

Jan

> --- a/xen/drivers/passthrough/amd/iommu_init.c
> +++ b/xen/drivers/passthrough/amd/iommu_init.c
> @@ -558,7 +558,7 @@ static void parse_event_log_entry(struct amd_iommu 
> *iommu, u32 entry[])
>              return;
>          }
>          udelay(1);
> -        rmb();
> +        barrier(); /* Prevent hoisting of the entry[] read. */
>          code = get_field_from_reg_u32(entry[1], IOMMU_EVENT_CODE_MASK,
>                                        IOMMU_EVENT_CODE_SHIFT);
>      }
> @@ -663,7 +663,7 @@ void parse_ppr_log_entry(struct amd_iommu *iommu, u32 
> entry[])
>              return;
>          }
>          udelay(1);
> -        rmb();
> +        barrier(); /* Prevent hoisting of the entry[] read. */
>          code = get_field_from_reg_u32(entry[1], IOMMU_PPR_LOG_CODE_MASK,
>                                        IOMMU_PPR_LOG_CODE_SHIFT);
>      }
> -- 
> 2.1.4




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