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SubjectRe: [PATCH] iommu: Implement deferred domain attachment
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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

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