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Cc:     baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org,
        jroedel@suse.de, linux-kernel@vger.kernel.org,
        Tom Murphy <murphyt7@tcd.ie>
Subject: Re: [PATCH] iommu: Implement deferred domain attachment
To:     Joerg Roedel <joro@8bytes.org>
References: <20200515094519.20338-1-joro@8bytes.org>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <8ce93a10-2ce0-e5a0-88a0-5d21d7003c0f@linux.intel.com>
Date:   Fri, 15 May 2020 21:51:03 +0800
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Hi Joerg,

On 2020/5/15 17:45, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> The IOMMU core code has support for deferring the attachment of a domain
> to a device. This is needed in kdump kernels where the new domain must
> not be attached to a device before the device driver takes it over.
> 
> But this needs support from the dma-ops code too, to actually do the
> late attachment when there are DMA-API calls for the device. This got
> lost in the AMD IOMMU driver after converting it to the dma-iommu code.
> 
> Do the late attachment in the dma-iommu code-path to fix the issue.
> 
> Cc: Jerry Snitselaar <jsnitsel@redhat.com>
> Cc: Tom Murphy <murphyt7@tcd.ie>
> Reported-by: Jerry Snitselaar <jsnitsel@redhat.com>
> Tested-by: Jerry Snitselaar <jsnitsel@redhat.com>
> Fixes: be62dbf554c5 ("iommu/amd: Convert AMD iommu driver to the dma-iommu api")
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>   drivers/iommu/iommu.c | 33 +++++++++++++++++++++++++++------
>   1 file changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 4050569188be..f54ebb964271 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1889,13 +1889,19 @@ void iommu_domain_free(struct iommu_domain *domain)
>   }
>   EXPORT_SYMBOL_GPL(iommu_domain_free);
>   
> -static int __iommu_attach_device(struct iommu_domain *domain,
> -				 struct device *dev)
> +static bool __iommu_is_attach_deferred(struct iommu_domain *domain,
> +				       struct device *dev)
> +{
> +	if (!domain->ops->is_attach_deferred)
> +		return false;
> +
> +	return domain->ops->is_attach_deferred(domain, dev);
> +}
> +
> +static int __iommu_attach_device_no_defer(struct iommu_domain *domain,
> +					  struct device *dev)
>   {
>   	int ret;
> -	if ((domain->ops->is_attach_deferred != NULL) &&
> -	    domain->ops->is_attach_deferred(domain, dev))
> -		return 0;
>   
>   	if (unlikely(domain->ops->attach_dev == NULL))
>   		return -ENODEV;
> @@ -1903,9 +1909,19 @@ static int __iommu_attach_device(struct iommu_domain *domain,
>   	ret = domain->ops->attach_dev(domain, dev);
>   	if (!ret)
>   		trace_attach_device_to_domain(dev);
> +
>   	return ret;
>   }
>   
> +static int __iommu_attach_device(struct iommu_domain *domain,
> +				 struct device *dev)
> +{
> +	if (__iommu_is_attach_deferred(domain, dev))
> +		return 0;
> +
> +	return __iommu_attach_device_no_defer(domain, dev);
> +}
> +
>   int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>   {
>   	struct iommu_group *group;
> @@ -2023,7 +2039,12 @@ EXPORT_SYMBOL_GPL(iommu_get_domain_for_dev);
>    */
>   struct iommu_domain *iommu_get_dma_domain(struct device *dev)
>   {
> -	return dev->iommu_group->default_domain;
> +	struct iommu_domain *domain = dev->iommu_group->default_domain;
> +
> +	if (__iommu_is_attach_deferred(domain, dev))
> +		__iommu_attach_device_no_defer(domain, dev);

It seems that the return value needs to be checked. The default domain
is invalid if attach() failed.

Best regards,
baolu