linux-kernel - Re: [PATCH v13 4/6] iommu/vt-d: Add support for IOMMU default DMA mode build options

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Date:   Thu, 17 Jun 2021 15:32:23 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org, robin.murphy@....com,
        corbet@....net
Cc:     baolu.lu@...ux.intel.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linuxarm@...wei.com,
        thunder.leizhen@...wei.com, chenxiang66@...ilicon.com,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v13 4/6] iommu/vt-d: Add support for IOMMU default DMA
 mode build options

On 6/16/21 7:03 PM, John Garry wrote:
> @@ -4382,9 +4380,9 @@ int __init intel_iommu_init(void)
>   		 * is likely to be much lower than the overhead of synchronizing
>   		 * the virtual and physical IOMMU page-tables.
>   		 */
> -		if (!intel_iommu_strict && cap_caching_mode(iommu->cap)) {
> -			pr_warn("IOMMU batching is disabled due to virtualization");
> -			intel_iommu_strict = 1;
> +		if (cap_caching_mode(iommu->cap)) {
> +			pr_warn("IOMMU batching disallowed due to virtualization\n");
> +			iommu_set_dma_strict(true);

With this change, VM guest will always show this warning. How about
removing this message? Users could get the same information through the
kernel message added by "[PATCH v13 2/6] iommu: Print strict or lazy
mode at init time".

Best regards,
baolu