Re: [PATCH] iommu/amd: Do not clear event/ppr log buffer when snp is enabled

[Joerg Roedel <joro@8bytes.org>]

On Thu, Jan 05, 2023 at 09:18:04AM +0000, Vasant Hegde wrote:
> -	memset(__evt, 0, 4 * sizeof(u32));
> +	if (!amd_iommu_snp_en) {
> +		/*
> +		 * To detect the hardware errata 732 we need to clear the
> +		 * entry back to zero.
> +		 */
> +		memset(__evt, 0, 4 * sizeof(u32));
> +	}

This needs a comment that the buffers are not writeable with SNP
enabled.

>  }
>  
>  static void iommu_poll_events(struct amd_iommu *iommu)
> @@ -736,10 +742,11 @@ static void iommu_poll_ppr_log(struct amd_iommu *iommu)
>  		entry[1] = raw[1];
>  
>  		/*
> -		 * To detect the hardware bug we need to clear the entry
> -		 * back to zero.
> +		 * To detect the hardware errata 733 we need to clear the
> +		 * entry back to zero.
>  		 */
> -		raw[0] = raw[1] = 0UL;
> +		if (!amd_iommu_snp_en)
> +			raw[0] = raw[1] = 0UL;

Same here.

>  
>  		/* Update head pointer of hardware ring-buffer */
>  		head = (head + PPR_ENTRY_SIZE) % PPR_LOG_SIZE;
> -- 
> 2.31.1
>