linux-kernel - Re: [PATCH v13 6/6] iommu: Remove mode argument from iommu_set_dma

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Date:   Thu, 17 Jun 2021 15:36:52 +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 6/6] iommu: Remove mode argument from
 iommu_set_dma_strict()

On 6/16/21 7:03 PM, John Garry wrote:
> We only ever now set strict mode enabled in iommu_set_dma_strict(), so
> just remove the argument.
> 
> Signed-off-by: John Garry <john.garry@...wei.com>
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> ---
>   drivers/iommu/amd/init.c    | 2 +-
>   drivers/iommu/intel/iommu.c | 6 +++---
>   drivers/iommu/iommu.c       | 5 ++---
>   include/linux/iommu.h       | 2 +-
>   4 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index fb3618af643b..7bc460052678 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3099,7 +3099,7 @@ static int __init parse_amd_iommu_options(char *str)
>   	for (; *str; ++str) {
>   		if (strncmp(str, "fullflush", 9) == 0) {
>   			pr_warn("amd_iommu=fullflush deprecated; use iommu.strict instead\n");
> -			iommu_set_dma_strict(true);
> +			iommu_set_dma_strict();
>   		}
>   		if (strncmp(str, "force_enable", 12) == 0)
>   			amd_iommu_force_enable = true;
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index d586990fa751..0618c35cfb51 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -454,7 +454,7 @@ static int __init intel_iommu_setup(char *str)
>   			iommu_dma_forcedac = true;
>   		} else if (!strncmp(str, "strict", 6)) {
>   			pr_warn("intel_iommu=strict deprecated; use iommu.strict instead\n");
> -			iommu_set_dma_strict(true);
> +			iommu_set_dma_strict();
>   		} else if (!strncmp(str, "sp_off", 6)) {
>   			pr_info("Disable supported super page\n");
>   			intel_iommu_superpage = 0;
> @@ -4382,7 +4382,7 @@ int __init intel_iommu_init(void)
>   		 */
>   		if (cap_caching_mode(iommu->cap)) {
>   			pr_warn("IOMMU batching disallowed due to virtualization\n");
> -			iommu_set_dma_strict(true);
> +			iommu_set_dma_strict();
>   		}
>   		iommu_device_sysfs_add(&iommu->iommu, NULL,
>   				       intel_iommu_groups,
> @@ -5699,7 +5699,7 @@ static void quirk_calpella_no_shadow_gtt(struct pci_dev *dev)
>   	} else if (dmar_map_gfx) {
>   		/* we have to ensure the gfx device is idle before we flush */
>   		pci_info(dev, "Disabling batched IOTLB flush on Ironlake\n");
> -		iommu_set_dma_strict(true);
> +		iommu_set_dma_strict();
>   	}
>   }
>   DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x0040, quirk_calpella_no_shadow_gtt);
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 60b1ec42e73b..ff221d3ddcbc 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -349,10 +349,9 @@ static int __init iommu_dma_setup(char *str)
>   }
>   early_param("iommu.strict", iommu_dma_setup);
>   
> -void iommu_set_dma_strict(bool strict)
> +void iommu_set_dma_strict(void)
>   {
> -	if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT))
> -		iommu_dma_strict = strict;
> +	iommu_dma_strict = true;

Sorry, I still can't get how iommu.strict kernel option works.

static int __init iommu_dma_setup(char *str)
{
         int ret = kstrtobool(str, &iommu_dma_strict);

         if (!ret)
                 iommu_cmd_line |= IOMMU_CMD_LINE_STRICT;
         return ret;
}
early_param("iommu.strict", iommu_dma_setup);

The bit IOMMU_CMD_LINE_STRICT is only set, but not used anywhere. Hence,
I am wondering how could it work? A bug or I missed anything?

Best regards,
baolu

>   }
>   
>   bool iommu_get_dma_strict(struct iommu_domain *domain)
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 32d448050bf7..754f67d6dd90 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -476,7 +476,7 @@ int iommu_enable_nesting(struct iommu_domain *domain);
>   int iommu_set_pgtable_quirks(struct iommu_domain *domain,
>   		unsigned long quirks);
>   
> -void iommu_set_dma_strict(bool val);
> +void iommu_set_dma_strict(void);
>   bool iommu_get_dma_strict(struct iommu_domain *domain);
>   
>   extern int report_iommu_fault(struct iommu_domain *domain, struct device *dev,
>